What temps to start using Tanis engine preheater?

[Morne]

Summer is most certainly behind us now, but it has yet to get really cold. I have a Tanis engine preheater on my Cessna 182E but am wondering when I should plug it in. Do I wait for the first frost?

What is everyone else's decision point for plugging in the engine preheat?

Yes, my bird is hangared.

 

[write-stuff]

Most people wait until it's pretty cold. I have the advantage of having my hangar in the front yard so it's not hard to get to. Because of that, I plug it in before flying when the temps get down to the mid 50s. Makes it really easy to start!

 

[zaitcev]

Local airplanes, parked outside, go on engine heater when temperatures drop below +5C overnight (e.g. a bit above freezing). Coincidentially it is the temperature at which manuals suggest start using primer in Cherokees. Heating is done so that airplanes are warm enough to start without a ground cart, and not to prevent block cracking from freezing as in automobiles. Note that batteries will be cold and their charge reduced.

 

[steingar]

I start plugging in my Cherokee when it hits the thirties. I also have a battery tender hooked up and plugged in when the aircraft isn't flying.

 

[alaskaflyer]

Around freezing. With my multi-viscosity oil, I'm more concerned about a warm battery for start than anything else at that temp.

 

[poadeleted20]

Over the years, I've found that the some people start preheating when the OAT is below 40F, and virtually everyone is at 20F, with a fairly linear slope between the two points.

 

[Ted]

I start plugging mine in below 40F if it's possible. Easiest thing to do is stop by the airport the night before, plug it in, and then it's all ready to go when you show up in the morning.

Of course, then there are the times I forget, and end up starting it when it's below 20F. Once I was at -20F parked outside. Not only was the plane plugged in, but it had sleeping bags over the engines!

 

[write-stuff]

If you have the opportunity, don't limit yourself to those near freezing days. You got the Tanis, so use it! Warm it up even when temps are much higher. Your engine will thank you for it.

 

[ScottM]

I use a thermo cube
http://sportys.com/pilotshop/product/9636

My plane has been plugged in for a month, but it only turns on when the temps drop below 35F.

I also have the battery minder plugged in, that is plugged in year round so no change for temperature there.

 

[Ted]

I use a thermo cube
http://sportys.com/pilotshop/product/9636

My plane has been plugged in for a month, but it only turns on when the temps drop below 35F.

I also have the battery minder plugged in, that is plugged in year round so no change for temperature there.

That is a really, really bad idea. What that ends up doing is creating a lot of condensation that will end up in your oil. This will corrode your engine something awful.

Someone at my airport had an IO-550 in his Mooney with one of those. The engine made it 150 hours (since factory reman from Continental) before he had to send it back in due to corrosion.

I would strongly suggest that you not use that.

 

[dmccormack]

That is a really, really bad idea. What that ends up doing is creating a lot of condensation that will end up in your oil. This will corrode your engine something awful.

Someone at my airport had an IO-550 in his Mooney with one of those. The engine made it 150 hours (since factory reman from Continental) before he had to send it back in due to corrosion.

I would strongly suggest that you not use that.

Ted - I think you're suggesting that constant warming then cooling cycles will cause condensation (accurate?)

So: the only time to actually set the preheat is the night before as it will not have to chance to extract enough ambient water vapor to cause corrosion -- but constant warm-cold-warm will cause a build up of condensation over time.

Hmmm... makes sense!

 

[poadeleted20]

For those unfamiliar, Ted probably knows more about the engineering side of our engines than anyone else here. Listen to him on stuff like this!

 

[Ted]

Ted - I think you're suggesting that constant warming then cooling cycles will cause condensation (accurate?)

Correct.

So: the only time to actually set the preheat is the night before as it will not have to chance to extract enough ambient water vapor to cause corrosion -- but constant warm-cold-warm will cause a build up of condensation over time.

Hmmm... makes sense!

It's the warming and cooling cycles that cause the condensation. If you just warm it without letting it cool, it won't condense.

And to clarify, this is something that's an issue over time. If you fly your plane often, condensation isn't an issue anyway. I know someone who does a similar technique with his plane, and he's had no condensation issues. He also flies his plane several times a week.

But as I recall, Scott doesn't fly his plane that often, and that's how most of us are. Even with the ~500 hours/year that I fly, it's not uncommon for the aircraft I take care of to sit for weeks at a time between flights. For example, the 310 has sat since September 25th (other than some maintenance) and tomorrow I'm flying it about 16 hours over the next 2 days. If I let a pre-heater tick on and off over the time periods I'm not flying it, I'm sure that the engines would suffer corrosion issues.

 

[ScottM]

That is a really, really bad idea. What that ends up doing is creating a lot of condensation that will end up in your oil.

In Illinois when it drops to 35 and the engine heater comes on it stay on for a while. It is not like it comes on for an hour and then turns off and then two hours later turns on again. I cannot see how this would cause anymore issues than running the engine for an hour, stopping for it to cool down while the pilot has lunch, and then running the engine again for an hour every day.

What usually happens is that late in the evening the temps drop, the heater turns on and stays on until it is warm again at around noon. This is no different than going out to the hangar the night before and plugging the heater in.

Here are some thing that Reiff has said on the topic.

That is why I have Reiff heater, I can leave that on without rotting the engine right??

We have been encouraging Aviation Consumer for years to conduct a study on this issue. Now they have...

PREHEAT AND CORROSION: NO SMOKING GUN

Aviation Consumer, March 2007, pg. 23​

We can't print the article due to their copyright, but you can buy a copy off their web site. Here are a few excerpts:

They instrumented a Continental 520 on a Bonanza that was equipped with our Standard System. The preheat system was plugged in and they recorded internal crankcase temperature and %RH (relative humidity) data over a 7 day span. During that period ambient temps ranged from teens to 30F.

Results... The internal RH started at 60%RH at ambient temperature. After about 12 hrs of heating it stabilized at about 120F and 15%RH and it held pretty constant for 7 days.

Conclusion... "These findings don't support the view that preheaters cause corrosion."

"Clearly, a preheater seems to dry the engine out, not cause it to behave like a terrarium."

"While our experiment is far from definitive and doesn't consider all possible ambient conditions, it does seem to show that far from causing corrosion, an always-on preheater actually appears to benefit the engine."

 

[dmccormack]

Not according to Tanis. And I have opened up the engine and found zero corrosion nor condensation.

Does Tanis recommend a thermostat such as the thermo cube?

 

[Skylane81E]

When in doubt preheat. A very large amount of the wear on the bottom end of the engine occurs at start up before the oil pressure reaches the bearings. The warmer your oil the faster it gets to the bearings.

I've been told to start at 40*F. I also recomend allowing cold oil to warm at lower RPM to reduce the load on the engine before things really start flowing.

 

[ScottM]

Does Tanis recommend a thermostat such as the thermo cube?

The guy at Reiff told me that they used to sell that very same device, but noticed a fair amount of returns for failures. I have had two and both worked as advertised.

 

[dmccormack]

I've been told to start at 40*F. I also recomend allowing cold oil to warm at lower RPM to reduce the load on the engine before things really start flowing.

Some engine manuals will specify a minimum RPM required to assure oil is flowing up and over what it needs to -- my O-145 Lycoming manual specified 800-1000 RPM which is faster than low idle (5-600 RPM).

 

[Ted]

In Illinois when it drops to 35 and the engine heater comes on it stay on for a while. It is not like it comes on for an hour and then turns off and then two hours later turns on again. I cannot see how this would cause anymore issues than running the engine for an hour, stopping for it to cool down while the pilot has lunch, and then running the engine again for an hour every day.

It's not the hour on/hour off that causes problems, it's when it's on for a longer period of time (say, evening through mid/late morning) and then off for that same period of time.

The difference is that if you run the engine for an hour, you've boiled out all the water from the system, same when you fly home. That's why engines that run every day don't have corrosion issues. The Tanis or Reiff systems will not boil off water in the oil.

What usually happens is that late in the evening the temps drop, the heater turns on and stays on until it is warm again at around noon. This is no different than going out to the hangar the night before and plugging the heater in.

Sure it is, because when you go fly the plane presumably after it's been plugged in overnight, and then that boils out all the water.

What ends up happening with your device is you heat up the engine, get more water in the crankcase, and then it'll cool off again. If your Reiff heater is like mine, it probably gets your engine up to, say, 80F, which is a lot warmer than the ambient temperature. The cycle that you talk about (on in the evening, off around noon) is exactly what causes corrosion issues.

Here are some thing that Reiff has said on the topic.

That is regarding leaving it plugged in all the time and operating over that 7-day period consistently. That is fine, and what you should do if you don't want to stop by the night before.. But systems like your method are what cause problems, because the temperatures don't climb and stabilize, they will fluctuate.

 

[Ted]

Does Tanis recommend a thermostat such as the thermo cube?

Not that I've seen.

 

[timwinters]

If you can hit the FBO's (or someone else's) Wifi at your hangar then you should check out the wifi outlet controllers. Just turn it on a few hours before you plan to fly.

Me? I have a home-made version of a red dragon. Mine pumps the hot air into the bottom of the cowl and the cockpit. I crank it up when I arrive at the plane and, by the time I'm done with the preflight, all my engine temps (including oil) are about 25dF above ambient. Works well for me since it doesn't get really cold here and, if it does, then I'm not flying!

 

[ScottM]

But systems like your method are what cause problems, because the temperatures don't climb and stabilize, they will fluctuate.

Have you seen any evidence of that causing problems? I ask because I have been doing this for several years and have seen no problems, no corrosion at all and have had the engine open to look. It is also very common around here and the mechanics I have talked to have never seen an issue either. Nor have we ever found a drop of water anywhere in the engine.

When the temps do warm up and the thermostat finally turns off the blanket around the cowl and the warmer temps slow the cooling process. That is not likely to result in condensation from my experience and observations.

I should add that I also have cylinder heaters as well as the oil pan heater. When the engine is plugged in it get warm all over. I also follow the advise of Reiff to unscrew the oil dipstick filler to help vent any moisture if there is any. Bottom line is that I am not worried about an occasional daily on and off. Most of time the heater will be on and like the study shows it make the engine drier, not wetter.

 

[dmccormack]

OK, counter-point:

If the engine is heated to high enough (?) temperatures and there is a vent there should be little vapor condensation.

Since, as the temps cool, the air in the engine will rise and escape through the vent, carrying water vapor. As the change in temperature is gradual, due to the insulation and the mass of the engine, there is little likelihood of condensation on the inner walls of the engine case.






Seem to be alot of "ifs" that have to work to avoid problems...

 

[ScottM]

OK, counter-point:

If the engine is heated to high enough (?) temperatures and there is a vent there should be little vapor condensation.

Since, as the temps cool, the air in the engine will rise and escape through the vent, carrying water vapor. As the change in temperature is gradual, due to the insulation and the mass of the engine, there is little likelihood of condensation on the inner walls of the engine case.






Seem to be alot of "ifs" that have to work to avoid problems...

I agree with all of that, including the ifs. Ted knows engines really well and if anyone has some real experimental data it would be him. All I have is a small sample of empirical data.

 

[dmccormack]

I agree with all of that, including the ifs. Ted knows engines really well and if anyone has some real experimental data it would be him. All I have is a small sample of empirical data.

I agree. Now that I'm closer to my hangar (15 minutes rather than 35), dropping by the night before isn't too big a deal.

I have an oil pan heater but the light bulb and blankets over the cowling works very well down to about 20 F.

 

[Ted]

Have you seen any evidence of that causing problems? I ask because I have been doing this for several years and have seen no problems, no corrosion at all and have had the engine open to look. It is also very common around here and the mechanics I have talked to have never seen an issue either. Nor have we ever found a drop of water anywhere in the engine.

I doubt that you're ever going to find a drop of water in the engine. Remember, as soon as you fly the plane long enough to get the oil up to proper operating temperature, the oil will boil off, and you don't pull the accessory housing and other bits off where the water will hide for routine inspections. If you visibly see water in the engine, then that means you're doing something really bad.

But yes, I have seen evidence of it causing problems - the IO-550 I mentioned in my first reply (you can imagine he wasn't happy), as well as experiments I've done. I managed to cause substantial damage to a brand new engine in less than a week by repeatedly getting the engine hot, freezing it, and repeating the process. Now, that was a very extreme case, but still basically what you're describing. We drained about 6 oz of water out of the oil every morning on that test.

Edit: The oil never got hot during the running, thus the water never boiled out. This was pretty much the absolute worst way you could treat your engine from a corrosion perspective.

When the temps do warm up and the thermostat finally turns off the blanket around the cowl and the warmer temps slow the cooling process. That is not likely to result in condensation from my experience and observations.

How exactly are you observing it? The condensation will occur inside the engine, where you can't see it. It's not like a soda can that's coming out of the fridge on a warm day. You won't see it visibly.

I should add that I also have cylinder heaters as well as the oil pan heater. When the engine is plugged in it get warm all over. I also follow the advise of Reiff to unscrew the oil dipstick filler to help vent any moisture if there is any. Bottom line is that I am not worried about an occasional daily on and off. Most of time the heater will be on and like the study shows it make the engine drier, not wetter.

If the heater is on most of the time anyway, then why not leave it on all the time for the winter? Per your Reiff data, that keeps it at an effectively constant temperature and RH. What exactly do you consider the benefit of your device to be, other than saving the FBO a couple pennies worth of electricity? The fact that you're heating the whole engine vs. just the oil pan I don't see as being particularly relevant.

It's your airplane, do what you want. In my experience, the way you choose to operate your pre-heater isn't advisable. Just sharing my experience.

 

[dmccormack]

What's interesting is my trusted A&P laughed at me when I told him I pre-heated my O-145.

He said, "That thing's so small it's not going to take much running to warm up anyway -- plus by warming the block you just let all the oil run down instead of coating everything."

Hmmmm.....

 

[ScottM]

I managed to cause substantial damage to a brand new engine in less than a week by repeatedly getting the engine hot, freezing it, and repeating the process. Now, that was a very extreme case, but still basically what you're describing. We drained about 6 oz of water out of the oil every morning on that test.

Not exactly what I am describing. I would be heating the engine up over a 12 hour period on average. Then when the ambient temp raises above 35F the heater turns off and the engine will cool to whatever temp is now above ambient which will be higher than freezing. The blanket will also slow the cooling down.

How exactly are you observing it? The condensation will occur inside the engine, where you can't see it.

You remember all the fun I have had with ECI cylinders and their ADs? I got to several times take the airplane top apart and get a good look inside.

It's your airplane, do what you want. In my experience, the way you choose to operate your pre-heater isn't advisable. Just sharing my experience.

Understand. I appreciate your input.

 

[Ted]

What's interesting is my trusted A&P laughed at me when I told him I pre-heated my O-145.

He said, "That thing's so small it's not going to take much running to warm up anyway -- plus by warming the block you just let all the oil run down instead of coating everything."

Hmmmm.....

I'm not sure that your mechanic really gets what the true point of pre-heating is. The benefit is the reduction of the wear that occurs during a cold start. The engine has much less wear on a warmer start. Everything moves easier, oil gets through the engine faster, etc.

The oil running down is somewhat accurate. That's one of the reasons why single-viscosity oil does better on engines that don't fly as often. It does a better job of coating everything, and providing better protection than the multi-visc, which will be thinner at cooler temps.

 

[dmccormack]

I'm not sure that your mechanic really gets what the true point of pre-heating is. The benefit is the reduction of the wear that occurs during a cold start. The engine has much less wear on a warmer start. Everything moves easier, oil gets through the engine faster, etc.

The oil running down is somewhat accurate. That's one of the reasons why single-viscosity oil does better on engines that don't fly as often. It does a better job of coating everything, and providing better protection than the multi-visc, which will be thinner at cooler temps.

I think his point is that the tolerances are so loose in these old engines (basically tractor technology) that the only wear protection possible is the thick oil coating the moving parts on startup, and that the fairly lightweight case allows the engine to warm up evenly and quickly.

Of course we're talking 25-45 degree ambient temps. It's very hard start unless preheated under 25 F because it's so hard to swing the prop!

 

[Ted]

I think his point is that the tolerances are so loose in these old engines (basically tractor technology) that the only wear protection possible is the thick oil coating the moving parts on startup, and that the fairly lightweight case allows the engine to warm up evenly and quickly.

Of course we're talking 25-45 degree ambient temps. It's very hard start unless preheated under 25 F because it's so hard to swing the prop!

Interesting theory. But I think it's probably pretty much a moot point, since as you pointed out it's hard to start without preheat under 25F.

 

[Skylane81E]

I've been thinking about the condensation issue for a bit and here's my input, worth exactly what you paid for it.

Unlike when you run the engine an electric heater isn't making water. So as you warm the engine it shouldnt get much wetter. Some the relative humidity will exchange over as the air warms inside the engine but not much. So for a relatively short term there isn't likely to be much condensation as you wont be adding much water. Ie I think you are both right.

Now warming the engine when you aren't going to fly it will encourage the oil to run off parts and at the very least wastes power. The engine doesn't mind being cold if its just parked.

 

[Capt. Geoffrey Thorpe]

But yes, I have seen evidence of it causing problems - the IO-550 I mentioned in my first reply (you can imagine he wasn't happy), as well as experiments I've done.

The rate of corrosion increases with temperature.

Instead of heating the engine when it is unused during the winter. One should be freezing the engine for storage during the summer.

 

[write-stuff]

Forgetting about the dissimilar metals and whether or not oil has coated the innards, a warm engine is very likely to start easier and smoother than a cold-soaked one. Like I said, if you've got the Tanis, use it.

 

[steingar]

No good reason not to. The damn things are expensive too.

 

[dmccormack]

Forgetting about the dissimilar metals and whether or not oil has coated the innards, a warm engine is very likely to start easier and smoother than a cold-soaked one. Like I said, if you've got the Tanis, use it.

Ignoring the battery, what difference does it make if the engine parts are cold? Assuming overall contraction in cold, then gradual expansion when initially running -- aren't they made for that?

I've heard about "well, the cold start means metal is rubbing against metal!"

Isn't that true for every start unless you have some sort of pre-oiler?

(No point to make -- just asking)

 

[denverpilot]

Dissimilar metals expand at different rates when heated rapidly.

 

[dmccormack]

Dissimilar metals expand at different rates when heated rapidly.

That's the issue -- how rapidly?

I'm asking about a small, 65 HP engine, mind.

 

[kyleb]

That's the issue -- how rapidly?

I'm asking about a small, 65 HP engine, mind.

I don't have those tables handy, but aluminum is a much better conductor of heat than steel and has a significantly higher coefficient of thermal expansion. So the alumium parts will heat up faster, and expand more than the steel parts. Your problem comes during the warm up phase. During that period, the aluminum stuff has outgrown the steel stuff and the clearances are probably the fartherest from normal operating conditions.

Another thing which relates to something you asked earlier. Oil provides a cushion between metal parts. Also, it transfers heat between the hot and cold parts and helps to equalize temperatures in various components and areas of the engine. So you want the oil to flow, which means it needs to be reasonably warm. Which is why preheating is advised. I use a Reiff sump heater on the RV (with cowl plugs and a blanket). I'll do something similar whenever I get the Aeronca bolted together.

 

[denverpilot]

Thank goodness for multi-viscosity oil. We pre-heat but I suspect that oil not flowing well, is a large contributor to damage in cold weather ops.

Lots of folks don't realize there's oil coolers designed for normal temperatures and ones designed for colder temps that have better flow/bypass characteristics too. And winterizing plates for oil coolers.

Unfortunately we have the standard variety oil cooler and no winterizing plate, but again... we pre-heat... and our oil temps stay above the point where water/condensation will boil out of the system.

Seeing a bulged/burst oil cooler is an interesting sight. Makes a god-awful mess from what I've heard, too. Pumping all the oil overboard probably doesn't help engine longevity much, either.