Engineer Ted's How to Make Your Engine Last (while running)

Discussion in 'Maintenance Bay' started by Ted DuPuis, Jan 27, 2013.

  1. Ted DuPuis

    Ted DuPuis Administrator Management Council Member

    Joined:
    Oct 9, 2007
    Messages:
    21,783
    Location:
    Paola, KS
    Display Name:

    Display name:
    iBanYou
    Well, it's the moment you've all been waiting for. Below is my list of recommendations for how to make your engine last while it's running. Yes, we will be addressing LOP and ROP. I am hoping this will be worthy of a sticky to match the "ground" thread, and provide a good reference for pilots of piston aircraft. This will focus on things that you can do in your operation of your engine to make it last longer. This will not cover things that fail that aren't your fault, and assumes that you were smart enough to put oil in the engine at a rate faster than it leaks/burns. Also, to go into full details of engine operation is beyond the scope of this writing, so there will be a few specifics, but mostly general rules. First, some background.

    Fundamentally, there are two primary things that kill engines (assuming you put oil in them): temperature and pressure. Temperature kills engines by weakening parts, making them more susceptible to damage (and damaging them directly). In some cases, temperatures. Pressure is force, which when exerted on parts can break them.

    Temperature and pressure are also two facts of engine operation. Internal combustion engines take a fuel and burn it, creating heat. Gasses heat up, increasing pressure in the cylinder. That high pressure pushes down on the piston, through the connecting rod, to the crankshaft, causing the crankshaft (and thus the propeller) to spin. This is the simplified version, obviously. The point is that you can't have an engine without temperature and pressure.

    Given the above background, the primary question for engine longevity comes down to how to best manage temperature and pressure. We'll go through the phases of flight.

    1) Start-up/Warm-up:

    When starting your plane, an idle of around 1,000 RPMs is good. If you're routinely hitting 2,000 on your starts, stop it. Figure out how to hit lower. Your car may hit 2,000 RPM on start, but your car probably also uses significantly thinner oil than your plane does and has an engine that is designed in such a way that it is more tolerant. It takes a bit of time for the oil to get pumped through these large engines. Also, at 2,000 RPM, your engine is putting a lot more heat out than your car engine is, since your plane engine is having to turn a prop and not simply spin at idle.

    You do want to let your oil temperature get into the green prior to takeoff. This has to do with making sure the engine is warmed up with clearances being what they're designed to be, as well as making sure that you don't accidentally run into an overpressure situation. Pre-heating minimizes the time required for this, so that's another benefit. Turbo engines (especially GTSIO-520s) care more about warm-up time, 172 engines care less. Some factory oil temperature gauges aren't very useful in this regard, so one must guess. My Aztec was this way.

    2) Takeoff/climb/cruise

    For takeoff, one should apply power smoothly and steadily. I see a lot of people just slam the throttle forward. On certain trainers this is less of an issue because they don't make much power, have no counterweights on the crankshaft, and have a fixed-pitch prop. In spite of this, a slow, steady throttle advance is a good habit to get into. Certain larger engines have dynamic counterweights, which are essentially pieces of metal attached to the crankshaft that will swing around to absorb vibrations. Because these aren't fit rigidly and are designed to move, too rapid of an acceleration can cause damage to them. On higher power engines especially, there is some concern about "shock heating", that is going from idle power to takeoff power very rapidly with the associated increase in heat from such a change. Some would argue this point just as they argue shock cooling. I know that it's more professional to make gradual power changes and the passengers like it better, so it's just good practice whether or not you think it matters. In my opinion, it certainly doesn't do anything good for the engine to make rapid power adjustments. I generally do my accelerate to takeoff power in 1-2 seconds. This doesn't have to a rolling throttle up, so you can hold the brakes if you've got a short runway to work with.

    Now we get into the most controversial part: the LOP/ROP discussion and power settings.

    What you want to use for climb and cruise settings will vary somewhat depending on your personal preference for speed vs. economy and reliability, as well as the specifics of the engine you're flying. For example, a 172 with a fixed pitch prop is fine to leave at full throttle from takeoff until you need to slow down. For most naturally aspirated engines, there's not much (if any) harm in leaving them at full throttle, provided you are keeping temperatures reasonable. As you climb in altitude, power will drop off naturally. In the Aztec, for instance, I went full throttle for takeoff, sync'd up the props at 2500 RPM, and just did my climb that way. Pull the props back to 2300 RPM for cruise. Throttles didn't come back until it was time for descent.

    When you're flying a plane with a big turbocharged engine, you usually don't want to have more than an 85% climb power setting. In many cases, full power is allowable continuously without any restrictions, so theoretically you could maintain full power in the climb. Remember back to the background statement of what kills engines: temperature and pressure. To make rated power, you need the highest pressures in the engine, leading to the most wear and tear on components. In the Navajo, I would pull back from takeoff power to climb power at 500 ft. Then, climb at an airspeed faster than Vy. More airflow over the engines will make them cooler and happier. You can usually have a fairly significant airspeed reduction for not a big sacrifice in climb rate. Your engines are happier and you're going faster. What's not to like?

    Does it make sense to climb at a lower power setting? That depends on your goals. Typically, I want to get up to altitude quickly, doubly so if there's a good tailwind up there. I haven't found low power/LOP climbs to be particularly useful most of the time because, although you do save some small amount of fuel, by that point you usually are cutting significantly into your climb performance, increasing your time to climb. Total block fuel burn probably balances out and block times probably go up a bit. Now, this is not to be confused with pulling back to a “standard” climb power. For example, in the short Navajo we used 35” and 2400 RPM, at 25 GPH per side for a climb power. Rated was around 42”, 2575 RPM, and 50 GPH per side. You don't want to climb at full power!

    For cruise power, typically 75% power is the maximum setting that you want to run for a naturally aspirated engine, and 65% for a turbocharged engine. Again, there is a good amount of variability here. The rule of thumb that at 65% power you pretty much can't hurt an engine has a decent bit of merit. Yes, there are engines for which this seems a bit odd. For example, a parallel-valve IO-540 can make 260 HP, 250 HP, or 235 HP, and the only difference is the rated RPM. On the whole, it is a good rule of thumb, though, and worthy of note.

    When you get into turbocharged engines, typically different power ratings have other changes to the engine in the form of different turbochargers, intercoolers, etc., all of which impact that temperature and pressure relationship that produces wear and tear. Stick to a percent power for that rating, and don't assume that just because an engine you think is identical makes more or less power that it actually is identical. In the Navajo I flew on 135, we'd fly 75% power and burn a ridiculous amount of fuel to do it. Why? The boss was paying the bills, and he wanted to. When I was flying the Navajo for Cloud Nine trips, we flew it at 65% power, and burned about 15 GPH less to go 10 kts slower. This was still ROP!

    In the 310, we fly at what comes out to around a 75% power LOP. The primary reason for this power setting is that it gets us about 10 kts more cruise speed than we'd see from a 65% power. For the kinds of trips we do, the extra speed for a marginal increase in fuel burn is worthwhile, even though it does decrease our fuel efficiency.

    At no point do I want to see CHTs exceed 380F. Continental recommends 380F as their maximum. Lycoming recommends 400F in cruise and 425F in climb as their maximum CHT. The limits are much higher, but these are goals. Remember, the goal here is more longevity. I have applied this rule to multiple airplanes with many different engine types, and they all have thanked me. For TIT/EGT I aim to keep below 1550F at all times, and for some aircraft and engine combinations, even lower. We flew the Navajo at 1450F TIT. As a rule, cooler is better.

    Now, the big question: Does it matter if I fly ROP or LOP? Will either one kill the engine?

    If done properly, ROP or LOP will work just fine and not kill your engine. In fact, you will have good longevity with either one (again, done properly). Here's why:

    Remember the two main things that cause wear on engines: temperature and pressure. The most important thing for your engine, regardless of whether you run it ROP or LOP, is to keep the temperatures and pressures reasonable. You know what temperatures are in the form of CHT, EGT, and TIT. Pressures will correlate with temperatures for all other conditions equal. Keep your temperatures happy, and as a rule, your engine will be happy, provided you're also not using excessive power settings.

    Detonation is a big concern that will kill engines. While it's outside of the scope of this post to go into detonation in detail, the rule of thumb that if you're at 65% power or below you won't have detonation issues is true for virtually all aircraft engines, certainly all the ones I've seen. If you have a big turbocharged engine, don't lean out at takeoff power.

    There are benefits to each and reasons why you might want to run ROP vs LOP. Engine wise, an engine that runs LOP will suffer less plug fouling. An engine that runs ROP will often hide some ignition system issues, since a rich mixture is easier to ignite than a lean mixture. So, you will likely see more misfires with engines running LOP. Since power drops off more quickly when LOP, depending on outside air temperature and other conditions, it may be more difficult to reach the CHTs you're looking for LOP without losing a great deal of airspeed, and it can be more workload intensive. I know some pilots who choose to fly ROP for the purpose of simplicity alone. Either one, if done properly, will give you good longevity. The main key comes down to respecting temperatures and making sure you stay out of detonation. Get educated on the specifics that work for your airplane.

    I'm not going to go into the specifics of how you should run ROP or LOP. Each airplane is different, and while the techniques are the same, the fine points are typically a bit different for each. Suffice it to say you usually want to be greater than 100F ROP or less than peak for most engines, respecting power setting and temperature recommendations already given. For certain engines and certain power settings, that still won't work. Know your airplane! Detonation is a real concern for certain aircraft engines, and you need to be wary of it.

    3) Descent/landing

    The primary consideration here is the old question of shock cooling, and whether it is best to pull the power back slowly or if it matters. As with above, dynamic counterweights don't like rapid changes in power, but certainly going from cruise power to idle in around 1-2 seconds won't hurt anything as far as counterweights go.

    The old rule of thumb with shock cooling is to reduce power 1" per minute to keep temperatures reducing at a reasonable rate.

    Now, there are a few things to keep in mind here. The first one is that, if you are doing what was outlined above to keep your CHTs/EGTs/TITs low and happy, that will also mean that the difference between operating temperature in cruise and at a descent/approach power is minimal. I think that the shock cooling issue probably came up more with turbo engines that were being run hot and hard, and were therefore more susceptible to damage from a rapid temperature change. Meanwhile, an O-360 seems to have no problem getting power cut to idle rapidly all day long in the pattern with students. Either way, the theory about shock cooling is that it will typically manifest itself not in cylinders falling off, but gradually with decreased longevity over time, cracks in the crankcase, etc.

    My opinion is that gradual power reductions and allowing your temperatures to drop slowly to prevent what is known as "shock cooling" makes sense, regardless of whether or not it is the plague some make it out to be. Again, it's more professional and passengers like it more. Plus, it makes sense that letting the engine - the whole engine, which goes beyond the CHTs, EGTs, and TITs - cool gradually can only be beneficial for it, or at the very worst not help at all. So I would advocate decreasing power at 1"/minute roughly, and behaving as though shock cooling does exist.

    I also typically will push the mixture full rich (gradually) and/or open the cowl flaps when the landing gear comes down. Gear slows the plane down, and then pushing the mixture to full rich helps to keep the engine about where it was for CHTs despite the reduced airflow, and also reduces EGTs/TITs, and lowers internal combustion pressures, cooling the pistons. An engine monitor is the biggest asset you can have in helping to determine what the true temperatures are in your aircraft. Most factory gauges aren't particularly accurate and give you limited information at best. As an example, the engine monitor in the Aztec taught me that when I put the gear down I should open the cowl flaps to full to keep the engines cool. On the 310 there are no cowl flaps, so I push the mixtures rich.

    4) Parking/shutdown

    Nothing really special here. For a turbo engine, you do want to let the engine cool down for 3 minutes. The purpose here is to get oil going through the turbo to cool it off from its higher temperature to a more reasonable temperature and help prevent coking. Sometimes it still happens, yes. If you're naturally aspirated, the normal taxi to your hangar and to get settled is enough time to let the pistons cool down, and then you're just fine pulling the mixture back and shutting things off.

    Now, how much does all of this matter? In the course of flying, you won't be able to do everything ideally for the life of the engine. That's fine. The thing to remember with engines is that they work mostly on cumulative wear, not instantaneous. With few exceptions, there is little you can do to kill an engine within minutes. It's possible, but rare. So, take the best care of your engine you know how, use the above as a guide to help you, and you will likely get good longevity out of your engine.
     
  2. LDJones

    LDJones Touchdown! Greaser!

    Joined:
    Sep 6, 2011
    Messages:
    10,821
    Location:
    Twin Cities, MN
    Display Name:

    Display name:
    Jonesy
    Wow....great write-up, Ted. Thanks!
     
  3. Alexb2000

    Alexb2000 En-Route

    Joined:
    Nov 28, 2010
    Messages:
    3,530
    Location:
    Dallas, TX
    Display Name:

    Display name:
    Alexb2000
    I generally do most of what you suggested.

    Sometimes the hardest thing is letting it warm up all the way, especially in the mountains.

    Anyway, on climb out I just let it go. I usually run ~38" (top of the green) to the flight levels if that's where I'm going. Temps are very cool even leaving Vegas on an August afternoon CHT's in the 330's, and TIT's in the 1200 range.

    Perhaps the cooling specific to the airframe has as much to do with it as engine type?
     
  4. Ted DuPuis

    Ted DuPuis Administrator Management Council Member

    Joined:
    Oct 9, 2007
    Messages:
    21,783
    Location:
    Paola, KS
    Display Name:

    Display name:
    iBanYou
    The warm-up time is the hard one, agreed.

    Remember that your temps will be a function of mixture, power setting, and cooling. I'd expect your CHT/TITs to be about where you state since I'm guessing you're full rich or close to it. The AJ1A has good cooling overall, although the top intake does block airflow to certain parts of the heads which will sometimes show evidence in the form of discoloration of the paint.

    Your cylinder pressures will still be high, and so that will have some wear and tear on the engine. It's worth noting that, during the crank issues, the AJ1A did have several snapped cranks indicative of this, and some AJ1As have had pretty nasty detonation cases, but usually due to timing being improperly set or a clogged injector.

    As I said, you need to balance your needs and desires. On the Chieftain we ran 40"/2400 for climb power (top of the green). Anything less and the plane just wouldn't climb at any substantial rate, which is why Piper increased the climb power setting from 35"/2400 that was used in the short Navajos. But we burned a lot of fuel doing it and I certainly wouldn't expect the engine to go past TBO. If I had a Navajo, I'd probably just accept the lower climb rates at 35" and then run a LOP cruise.
     
  5. ajstoner21

    ajstoner21 Cleared for Takeoff

    Joined:
    Oct 31, 2010
    Messages:
    1,344
    Location:
    Fort Worth, TX
    Display Name:

    Display name:
    Andrew
    Great write up Ted!
     
  6. Alexb2000

    Alexb2000 En-Route

    Joined:
    Nov 28, 2010
    Messages:
    3,530
    Location:
    Dallas, TX
    Display Name:

    Display name:
    Alexb2000
    Two more questions:

    Are you saying these cylinder pressures will put such wear on an engine that it won't go to TBO? Or is it just a factor for the guy trying to say, "I got 4000 hours before overhaul"?

    Last, is there a definitive way to see detonation on the engine monitor?
     
  7. Ted DuPuis

    Ted DuPuis Administrator Management Council Member

    Joined:
    Oct 9, 2007
    Messages:
    21,783
    Location:
    Paola, KS
    Display Name:

    Display name:
    iBanYou
    There are too many factors in making it to TBO to say that any one will kill your engine faster. As a rule, I'd say it more applies to the guy trying to hit 4000 SMOH. But then the other question is how you define making it. SR22Ts make TBO with two top overhauls in between. Is that making TBO or not?

    Not really. Typical signs of detonation are higher CHTs and lower EGTs. Detonation is also not an on-off switch, it's more of a slider. No detonation is good, but light detonation is typically tolerable and won't have a significant change in temperatures. It still releases pressure waves that will break down the ~3 micron air barrier between the metal and the actual combustion gasses. Even if you don't see much CHT change, more heat is going to the pistons, etc.

    If it's heavy detonation, you'll see it quickly with rapidly rising CHTs.
     
  8. aviatingfool

    aviatingfool Pre-takeoff checklist

    Joined:
    Dec 21, 2012
    Messages:
    201
    Display Name:

    Display name:
    aviatingfool
  9. Alexb2000

    Alexb2000 En-Route

    Joined:
    Nov 28, 2010
    Messages:
    3,530
    Location:
    Dallas, TX
    Display Name:

    Display name:
    Alexb2000
    Thanks!
     
  10. flyingcheesehead

    flyingcheesehead Touchdown! Greaser!

    Joined:
    Feb 23, 2005
    Messages:
    19,441
    Location:
    UQACY, WI
    Display Name:

    Display name:
    iMooniac
    Hmmm... I like the "mixture with the landing gear" trick. I'll have to start using that. Thanks Ted!
     
  11. Ted DuPuis

    Ted DuPuis Administrator Management Council Member

    Joined:
    Oct 9, 2007
    Messages:
    21,783
    Location:
    Paola, KS
    Display Name:

    Display name:
    iBanYou
    You're welcome! It's good for flows and cooling.

    You could also consider cowl flaps on the Mooney - I assume it has them like the F model did?
     
  12. Skylane81E

    Skylane81E Final Approach

    Joined:
    May 3, 2011
    Messages:
    8,059
    Location:
    Cincinnati
    Display Name:

    Display name:
    Duncan
    Now what about those of us with strait legs?!

    Guess I will have to keep it how it is, on final/last notch of flaps :goofy:
     
  13. Ted DuPuis

    Ted DuPuis Administrator Management Council Member

    Joined:
    Oct 9, 2007
    Messages:
    21,783
    Location:
    Paola, KS
    Display Name:

    Display name:
    iBanYou
    Upgrade! :D

    The real point is that you push the mixture rich for cooling purposes when you put a bunch of drag out. So, I'd say that works. :)
     
  14. iflyblog.com

    iflyblog.com Pre-takeoff checklist

    Joined:
    Sep 27, 2012
    Messages:
    151
    Location:
    Central Ohio
    Display Name:

    Display name:
    Brent
    Good post! I am still learning where best to run my IO-360 powered RV-8. Helpful advise.

    Thanks!
     
  15. flyingcheesehead

    flyingcheesehead Touchdown! Greaser!

    Joined:
    Feb 23, 2005
    Messages:
    19,441
    Location:
    UQACY, WI
    Display Name:

    Display name:
    iMooniac
    Nope. The Ovation has a carefully designed cooling system that uses these "blisters" around the exhaust:

    [​IMG]

    So, no cowl flaps. Those cause drag. ;)
     

    Attached Files:

  16. EdFred

    EdFred Touchdown! Greaser!

    Joined:
    Feb 25, 2005
    Messages:
    19,956
    Display Name:

    Display name:
    -
    Can you lean below 5000' as long as your CHTs are below a certain temperature without causing further damage to the engine?
     
  17. Ted DuPuis

    Ted DuPuis Administrator Management Council Member

    Joined:
    Oct 9, 2007
    Messages:
    21,783
    Location:
    Paola, KS
    Display Name:

    Display name:
    iBanYou
    Great question.

    There are a lot of variables in this. We know that a large number of high performance aircraft do typically lean out below 5,000 ft. The Navajo is an example - about 500 ft we'd pull back to 35", 2400 RPM, and 25 GPH a side. This was down from 42", 2575 RPM, and 45 GPH a side at takeoff.

    This rule of thumb existed primarily for naturally aspirated engines that were being flown without any sort of useful instrumentation. Think about an old 172 which had an oil temp gauge for engine temperature info and that's it. The general point was you don't know what your mixture really is and its impact on the engine, so play it safe and just run rich. For planes that lack useful instrumentation, the point is a good one and makes sense, so I would recommend that.

    Now let's take a plane that has an engine monitor. You know your CHTs, you know your EGTs. You don't know detonation for certain. Your Comanche has a parallel valve engine (low power per cylinder, very little if any detonation concern). In your case, I wouldn't worry about leaning below 5,000 ft. In fact, in my Aztec if I did a LOP climb I'd go take off, pull the props back to 2300 RPM, go LOP, and climb. That's 2300 RPM and 30". In a 172 with an engine monitor where you're at full throttle and whatever high RPM for climb I also wouldn't worry about it so long as you respect CHTs.

    It does also depend on power setting. So if you climb at 25"/2500 RPM, you can typically lean based on CHT, even in a high powered engine, regardless of altitude. Using the 310 as an example, though, I don't do that because if I do, the engines will overheat.

    What if you're cruising below 5,000 ft? Well, you'll have some sort of part throttle setting, and again I wouldn't worry about leaning causing issues, but again you really benefit from an engine monitor since it will tell you what's truly going on. But I would lean for cruise as I normally do at a lower altitude.

    There are a lot of variables here and the key is know your engine.
     
  18. Ted DuPuis

    Ted DuPuis Administrator Management Council Member

    Joined:
    Oct 9, 2007
    Messages:
    21,783
    Location:
    Paola, KS
    Display Name:

    Display name:
    iBanYou
    Interesting! Now I know. I figured they would have kept them since they were there in the earlier models and the later models had more power.
     
  19. Skylane81E

    Skylane81E Final Approach

    Joined:
    May 3, 2011
    Messages:
    8,059
    Location:
    Cincinnati
    Display Name:

    Display name:
    Duncan
    Ted, let me get your opinion on my climb out leaning technique.

    I have a 182 with the bone standard O470U, so I do have the "high" compression version. Factory EGT, CHT and oil temp installed.

    For full throttle operation I lean to a target EGT, 1200 or so, derived from what the gauge indicates at take off. My reasoning is that in that way I am doing the best I can to keep the mixture constant as I climb. This leaning starts as I clear TPA usually as the EGTs are already starting to drop off. This is the only time I use a target EGT. (Well not entirely true, I target 1400 for the corse lean in cruise, but I fine tune from that, aiming for 1400 first just saves time as I know that it will end up around there somewhere.)

    An engine monitor is on my wish list, but not in my plane.
     
  20. Ted DuPuis

    Ted DuPuis Administrator Management Council Member

    Joined:
    Oct 9, 2007
    Messages:
    21,783
    Location:
    Paola, KS
    Display Name:

    Display name:
    iBanYou
    Duncan,

    This is the same technique John Deakin typically recommends. On the whole and for your airplane it's probably sufficient. However, it depends on your plane. If I tried to do that with the 310, I'd roast the cylinders. But that's got injected 520s in a setup that has less cooling than it really needs.

    So, that's an "it depends" question. I've never tried it in a 182 with an engine monitor, so I don't know how well it would work.
     
  21. Skylane81E

    Skylane81E Final Approach

    Joined:
    May 3, 2011
    Messages:
    8,059
    Location:
    Cincinnati
    Display Name:

    Display name:
    Duncan
    Cool, I will keep doing it the, but will keep your cooling note in mind if I ever PPonk
     
  22. Ted DuPuis

    Ted DuPuis Administrator Management Council Member

    Joined:
    Oct 9, 2007
    Messages:
    21,783
    Location:
    Paola, KS
    Display Name:

    Display name:
    iBanYou
    You might want to ask Kent what he's found from operating the 182 with an engine monitor as well. Definitely a consideration if you PPonk. And we know more power is more better. ;)
     
  23. Skylane81E

    Skylane81E Final Approach

    Joined:
    May 3, 2011
    Messages:
    8,059
    Location:
    Cincinnati
    Display Name:

    Display name:
    Duncan
    Always so long as you don't tank your BSFC!
     
  24. flyingcheesehead

    flyingcheesehead Touchdown! Greaser!

    Joined:
    Feb 23, 2005
    Messages:
    19,441
    Location:
    UQACY, WI
    Display Name:

    Display name:
    iMooniac
    Pretty much, if you keep EGT at the takeoff value (you do at least have one EGT, right?), keep the cowl flaps open in the climb, and utilize a cruise climb when it's above 70ºF out, the 182's CHT's will remain below 400 without any further effort.
     
  25. Geico266

    Geico266 Touchdown! Greaser!

    Joined:
    Jun 15, 2008
    Messages:
    19,143
    Location:
    Husker Nation, NE
    Display Name:

    Display name:
    Geico
    Nice write up Ted. Good stuff.

    What are your thoughts on shock cooling?

    We have a jump plane that screams to 10,500', drops meat bombs and chops and drops. They do this over and over again.
     
  26. Ted DuPuis

    Ted DuPuis Administrator Management Council Member

    Joined:
    Oct 9, 2007
    Messages:
    21,783
    Location:
    Paola, KS
    Display Name:

    Display name:
    iBanYou
    I go into this above, and this is a source of never-ending debate. You see a lot of similar stories, and we also see 172s that do the same. But, these also tend to have low power engines in the first place - 180 hp or less from a 4 cylinder and 260 hp or less from a 6 cylinder. They probably also run at or near full rich, so their CHTs are likely a good bit below redline. You see the occasional 421 jump plane, but that's rare and I don't think they have great engine life.

    I think that the high-power engines when run hot and hard (figure someone with CHTs near limits), especially turbocharged, would be more likely to see effects from shock cooling than a 172. I've seen anecdotal evidence either way, but never anything definitive that proves one way or the other to me. Since shock cooling isn't supposed to be something that makes your cylinders fall off immediately but reduces cylinder life, you can't just thermally shock an engine, keep flying, and say that proves shock cooling doesn't exist. Meanwhile, you also can't look at your bill for a top overhaul or cracked crankcase and say that proves shock cooling does exist. There are too many factors.

    I do know that metals don't like rapid temperature changes, and I know that operating smoother tends to make passengers happier. So, I fly as though shock cooling is something I should worry about, and the worst outcome is my engines don't care and my passengers are happy. I don't obsess about it and have times when I need to chop-and-drop for various reasons, so I do. I keep my throttle movements smooth at all times. I've gotten good engine life, better than TBO and better than other folks, so I guess I'm doing something right.
     
  27. Skylane81E

    Skylane81E Final Approach

    Joined:
    May 3, 2011
    Messages:
    8,059
    Location:
    Cincinnati
    Display Name:

    Display name:
    Duncan
    Mechanic who came from a 182 jump operation reported that they treated cylinders like consumables and the usual cause for failure was cracking. Just one data point but data none the less.
     
  28. Ted DuPuis

    Ted DuPuis Administrator Management Council Member

    Joined:
    Oct 9, 2007
    Messages:
    21,783
    Location:
    Paola, KS
    Display Name:

    Display name:
    iBanYou
    As I said, you seem to see just as many people claiming problems as people who claim none. What the difference is, hard to say. Insufficient data to tell much.

    I'll be kind to my engines, though. So far they've all been kind back to me.
     
  29. Skylane81E

    Skylane81E Final Approach

    Joined:
    May 3, 2011
    Messages:
    8,059
    Location:
    Cincinnati
    Display Name:

    Display name:
    Duncan
    And there is the key, you won't hurt anything by thinking like shock cooling is real.

    My 430 has vertical planning, when the decent rate to target gets to about 500fpm the nose comes down and the power reduction to the traffic pattern is fairly gradual, and the increased airspeed in the decent increases cooling.

    I do have a habit of chopping the last bit of power out abeam the numbers and gliding in, but by the time I am there things have had a chance to cool off some.
     
  30. wickedsprint

    wickedsprint Pre-takeoff checklist

    Joined:
    Nov 20, 2012
    Messages:
    300
    Display Name:

    Display name:
    Wickedsprint
    I enjoyed your post, thanks for taking the time to write it.
     
  31. Ted DuPuis

    Ted DuPuis Administrator Management Council Member

    Joined:
    Oct 9, 2007
    Messages:
    21,783
    Location:
    Paola, KS
    Display Name:

    Display name:
    iBanYou
    Depends on how you do it and what you're starting from. I usually find temps have dropped from the ~380 normal to closer to 300 (for the hottest head), but I've been doing a gradual descent, power reductions, and then throw in cowl flaps and mixtures at the appropriate time. An engine monitor helps you greatly in this regard.

    Of course, your O-470 is also among the engines that is hard to kill.

    And correct, you'll never hurt something by thinking shock cooling does exist. By thinking it doesn't exist? The data is murky.

    You're welcome! :)
     
  32. coloradobluesky

    coloradobluesky En-Route

    Joined:
    Mar 19, 2014
    Messages:
    3,283
    Location:
    Colorado
    Display Name:

    Display name:
    coloradobluesky
    A lot of engines go through the top quart of oil fairly fast. So owners tend to keep it at 5 quarts instead of topping at 6. In the summer you should keep it at 6 if you are running hot. It will help cool your engine.
     
  33. flyingcheesehead

    flyingcheesehead Touchdown! Greaser!

    Joined:
    Feb 23, 2005
    Messages:
    19,441
    Location:
    UQACY, WI
    Display Name:

    Display name:
    iMooniac
    That greatly depends on how many quarts of oil your engine holds.
     
  34. gismo

    gismo Touchdown! Greaser!

    Joined:
    Feb 28, 2005
    Messages:
    12,665
    Location:
    Minneapolis
    Display Name:

    Display name:
    iGismo
    And AFaIK, increasing the oil quantity above what's needed to prevent an abnormally low level by the end of the flight does NOT improve cooling in many engines. It does follow that more oil in the sump means that each molecule of oil spends more time there but it may not become any cooler because the extra depth of the oil insulates the hotter oil on top. In addition, high oil levels lead to frothing (chances are this is why the oil level declines more quickly when topped off) which likely increases oil temps.
     
  35. SCCutler

    SCCutler Administrator Management Council Member PoA Supporter

    Joined:
    Feb 27, 2005
    Messages:
    16,091
    Location:
    Dallas
    Display Name:

    Display name:
    Spike Cutler
    Indeed. My 520 claims a 12 quart capacity, but if I fill to 12 quarts, that first quart is on the belly in an hour. The second, a couple. After that, stabilizes at the 9.5 to 10 quart mark.
     
  36. gismo

    gismo Touchdown! Greaser!

    Joined:
    Feb 28, 2005
    Messages:
    12,665
    Location:
    Minneapolis
    Display Name:

    Display name:
    iGismo
    AFaIK, there's actually a reason for that. I think the certification rules require enough oil capacity to allow for the worst case oil consumption rate (likely in the 1 qt/hr range on Bonanza engine) without going below the minimum oil quantity (probably 4 or 5 quarts in your engine) by the end of a max duration flight at "normal" cruise power. Fortunately the FAA never bothered to consider range extension from tip tanks and/or LOP operation in that calculation.
     
  37. Ted DuPuis

    Ted DuPuis Administrator Management Council Member

    Joined:
    Oct 9, 2007
    Messages:
    21,783
    Location:
    Paola, KS
    Display Name:

    Display name:
    iBanYou
    I'm not aware of the oil level and consumption certification requirement Lance mentions, but that doesn't mean it isn't there.

    As noted, engines have a "happy place" for oil level. Learn it and keep your oil there.
     
  38. tmyers

    tmyers En-Route

    Joined:
    Nov 8, 2012
    Messages:
    3,913
    Location:
    Kettering, OH
    Display Name:

    Display name:
    Tim Myers
    My IO-360 likes to be between 6 and 7 qts. I never put the 8th quart in at oil change and add as soon as I see it below the 6 qt mark.
     
  39. gismo

    gismo Touchdown! Greaser!

    Joined:
    Feb 28, 2005
    Messages:
    12,665
    Location:
    Minneapolis
    Display Name:

    Display name:
    iGismo
    I read about it somewhere, possibly on the internet so it must be true.
     
  40. EdFred

    EdFred Touchdown! Greaser!

    Joined:
    Feb 25, 2005
    Messages:
    19,956
    Display Name:

    Display name:
    -
    Bon Jour!

    I run my 540 around 6ish quarts. Anything more ends up on the bellah.