My O-470 runs cleaner with carb heat and low rpm

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MountainDude

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C182 with an O-470.
During my previous annuals, they told me my spark plugs had a lot of deposits and took a lot of effort to clean.
After listening to Mike Busch's podcast and reading some posts online, I decided to implement two strategies after my '24 annual:
1. Open carb heat in cruise, which apparently aerosolizes the fuel inside the carburetor better.
2. Run the lowest rpms I am comfortable with (this allows more time for the fuel to burn fully). Mike runs his at 1900 or 2000. Mine runs smoothly at 2100 (but not below), so I keep it there essentially the entire flight.

This year's annual I did not tell anything to my mechanic, but he noted that the spark plugs were very clean and wanted to know what I did.

Post update: I have always leaned heavily during taxiing.
 
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Our old 182Q used to seem to build up the most deposits when taxiing full rich. I got in the habit of leaning as far as possible after starting and also when exiting the runway after landing. That always seemed to help a lot.
 
You O-470 is carburerated. Adding heat is helping to evaporate the fuel and because you are leaning in cruise to the same Fuel Air Ratio you are not losing anything and gaining better combustion. Have you considered running LOP during cruise? Using carb heat during cruise should allow this. At 50F LOP you lose about 8% power and burn about 75% of the fuel, during cruise with about 4% loss of speed. You can do this below 65% power as long as your engine runs smooth Cylinder Head Temperature remains good. Running LOP also keeps the spark plugs cleaner and CHT lower if done correctly.

It is just a thought.
 
I never had much luck with LOP on the carbed 470, with or without carb heat shenanigans. If your plugs are getting fouled, assuming you're leaning properly in the air, you're not leaning on the ground and/or idling at too low a rpm to let the lead scavengers work.
 
I always leaned when taxiing the 182Q of a club I was in until the engine became a bit rough. That definitely helped with the build up. After that I flew with carb heat on whenever the engine monitor said the plane was in the right conditions for ice (because carb icing happened more times than I wanted to admit with that plane.)

I don't know about dropping down to 2100 other than to save fuel costs.
 
I know nothing about O-470s. I fly a Piper Warrior. I lean to near death on the ground and lean to stumble then enrichen to smoothness in cruise.

Try opening carb heat just a little, not wide open. I suspect it is not the heat that is helping to aerosolize the gas, but additional turbulence better mixing the mixture.
 
I too like to run my at lower RPM's. My 182R seems to lock in between 2100 and 2200. Prop is more efficient as lower speed. I have the 470U with JJA, so a tad more HP available vis a vis, but I've always used just a touch of carb heat (keep it out of the yellow), and a slight cocking of the throttle plate to keep the air turbulent, and my engine seems happy and runs smooth and cool. And of course lean it accordingly.
 
If your deposits are brownish-gray, it’s likely lead bromide. The solution is leaner and/or hotter. The ethylene dibromide in the fuel is doing what it’s supposed to - bromide attaching to the lead from tetraethyl lead and helping to exhaust it. Any early cooling allows it to condense instead of heading out the exhaust to coat your underbelly.
 
I use partial carb heat fairly often in our 182 (Pponk O470-50). I usually keep the carb temp in the mid-40s or higher. Another advantage we've found with using some carb heat is the fuel balance to the cylinders through the (primitive) induction system is better, and we get more even EGTs.
 
William Pete Hodges said:
You O-470 is carburerated. Adding heat is helping to evaporate the fuel and because you are leaning in cruise to the same Fuel Air Ratio you are not losing anything and gaining better combustion. Have you considered running LOP during cruise? Using carb heat during cruise should allow this. At 50F LOP you lose about 8% power and burn about 75% of the fuel, during cruise with about 4% loss of speed. You can do this below 65% power as long as your engine runs smooth Cylinder Head Temperature remains good. Running LOP also keeps the spark plugs cleaner and CHT lower if done correctly.

It is just a thought.
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I would love to run LOP, but my engine will not let me.
 
BigghHauss78 said:
I too like to run my at lower RPM's. My 182R seems to lock in between 2100 and 2200. Prop is more efficient as lower speed. I have the 470U with JJA, so a tad more HP available vis a vis, but I've always used just a touch of carb heat (keep it out of the yellow), and a slight cocking of the throttle plate to keep the air turbulent, and my engine seems happy and runs smooth and cool. And of course lean it accordingly.
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Thanks. What is "a touch of carb heat (keep it out of the yellow)"? I have a carb heat temp readout, but it does not have colored ranges.
 
Jeff Oslick said:
I use partial carb heat fairly often in our 182 (Pponk O470-50). I usually keep the carb temp in the mid-40s or higher. Another advantage we've found with using some carb heat is the fuel balance to the cylinders through the (primitive) induction system is better, and we get more even EGTs.
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That is also what I see. All my EGTs and CHTs are more even with carb heat.
 
I have a C182M with a Carb Temp Gauge. The TC data sheet and the book says to keep it between -15C and 5C (Yellow arc). P 3-3.
Leaning: My O470R is cold blooded and CHTs run in the low 300s unless it's a long hot climb out of high density altitude airports to mountain passes in the west, then the creep up to 350.

It is an 80 octane engine now on its second run SFREM at 1850 hrs (350 past TBO). I lean very aggressively on the ground and in flight. When 80 went away and 100LL was all that was available it would lead foul the bottom plugs to the point where every oil change they needed to be pulled and seriously cleaned or replaced. I ran ROP on 80 per book, and with 100LL ran LOP with carb temp set to 10C with selective carb heat. This engine makes ice on a hot day, so a little warmth in the throat is useful. I also ease the throttle back from WOT which seems to help balance the CHTs/EGTs. I eliminated the problem with mogas 87 or 91 octane lead/alcohol free fuel.

At cruise, I run lower RPMs, generally 2250 and 23" or best possible, and lean by the book, ie until rough and then enrichen till smooth with generally is about ±15º of peak. That kept the plugs relatively cleaner on 100LL. That pretty much follows @Jeff Oslick and @MountainDude's experience. When I got rid of 90% of its 100LL the oil lead levels dropped to the 200 levels and the fouling went away, and the engine builder proclaimed it was a very clean O470 at the 2700 (1200 past TBO) hr overhaul due to cam lobe wear.

The leaning technique went out the window when I installed the ElectroAire ignition system: It now just doesn't get rough above 6500' unless I lean until it starts missing. I have been too chicken to set it where I think it should be by the LOP -25 method, as the fuel burn is at 2.5 gph less than I'm accustomed to and the airspeed is about the same. I'm planning on taking the plane up and running it steady for an hour at various power settings to match the Cessna book settings and get actual burn rates and airspeeds, but it's a time consuming process and time is in short supply. I also see more even CHT/EGTs with partial carb heat. I haven't changed the engine temp sensors over to the Dynon yet, but when I do, I'll have more sophisticated recordings of what is actually happening in the engine.
 
greentips said:
I have a C182M with a Carb Temp Gauge. The TC data sheet and the book says to keep it between -15C and 5C (Yellow arc). P 3-3.
Leaning: My O470R is cold blooded and CHTs run in the low 300s unless it's a long hot climb out of high density altitude airports to mountain passes in the west, then the creep up to 350.

It is an 80 octane engine now on its second run SFREM at 1850 hrs (350 past TBO). I lean very aggressively on the ground and in flight. When 80 went away and 100LL was all that was available it would lead foul the bottom plugs to the point where every oil change they needed to be pulled and seriously cleaned or replaced. I ran ROP on 80 per book, and with 100LL ran LOP with carb temp set to 10C with selective carb heat. This engine makes ice on a hot day, so a little warmth in the throat is useful. I also ease the throttle back from WOT which seems to help balance the CHTs/EGTs. I eliminated the problem with mogas 87 or 91 octane lead/alcohol free fuel.

At cruise, I run lower RPMs, generally 2250 and 23" or best possible, and lean by the book, ie until rough and then enrichen till smooth with generally is about ±15º of peak. That kept the plugs relatively cleaner on 100LL. That pretty much follows @Jeff Oslick and @MountainDude's experience. When I got rid of 90% of its 100LL the oil lead levels dropped to the 200 levels and the fouling went away, and the engine builder proclaimed it was a very clean O470 at the 2700 (1200 past TBO) hr overhaul due to cam lobe wear.

The leaning technique went out the window when I installed the ElectroAire ignition system: It now just doesn't get rough above 6500' unless I lean until it starts missing. I have been too chicken to set it where I think it should be by the LOP -25 method, as the fuel burn is at 2.5 gph less than I'm accustomed to and the airspeed is about the same. I'm planning on taking the plane up and running it steady for an hour at various power settings to match the Cessna book settings and get actual burn rates and airspeeds, but it's a time consuming process and time is in short supply. I also see more even CHT/EGTs with partial carb heat. I haven't changed the engine temp sensors over to the Dynon yet, but when I do, I'll have more sophisticated recordings of what is actually happening in the engine.
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Thank you for sharing. That is a lot of useful info. Can you tell us more about the ignition system? Sounds like it may allow us to run O-470 LOP, which would be amazing. Saving 2.5 gph (with some small loss of TAS) would be great.
 
My O-520 likes a little carb heat too. Same thing, keep the temp sensor at about 35 to 38 F and the CHT's and EGT's are very consistent. My engine likes 2300rpm, I run about 17 to 18" MP, burning about 10.5gph at 9500. I often see CHT's with a maximum spread of 20 degrees.
 
Our 182L says the carb-heat air bypasses the filter. If that's the case, I would be hesitant to use it a lot during cruise; seems like a lot of non-filtered air could cause more problems with faster engine wear.
 
AV8R_87 said:
That was my initial thought, but how much stuff is in the air above 3000ft?
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I would think a lot. Especially in the South right now when they're burning the debris off the farm fields.
 
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Isn't that stuff fie enough to pass through an air filter anyway? Don't know for sure, just thinking out loud.
 
Not an A&P. But if the above discussion were about plugs in cars when leaded gasoline was still around, the discussion would quickly turn to "what plugs are you running, and what heat range?" Because to me, having to use carb heat in cruise to reduce fouling doesn't make sense...but I also have no experience with the o-470.
 
Albany Tom said:
Not an A&P. But if the above discussion were about plugs in cars when leaded gasoline was still around, the discussion would quickly turn to "what plugs are you running, and what heat range?" Because to me, having to use carb heat in cruise to reduce fouling doesn't make sense...but I also have no experience with the o-470.
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Its not about fouling. Its in the posts above, makes cht's run more consistent and smoother.
 
greentips said:
Leaning: My O470R is cold blooded and CHTs run in the low 300s unless it's a long hot climb out of high density altitude airports to mountain passes in the west, then the creep up to 350.
Click to expand...
Sounds a bit off - maybe double check where your CHT is located, have it calibrated? What kind of CHT probe/engine monitor do you have?

greentips said:
when I installed the ElectroAire ignition system:
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I'm kicking around the idea of adding an electronic ignition to my 0470-R. What lead you to get the ElectroAire vs SureFly?
 
Bell206 said:
I tend not to comment on how people operate their aircraft outside of what the OEM recommends. Which this thread appears to be about vs trying to troubleshoot a mx problem.
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Similarly, except that I would warn that increased induction temperatures increase the risk of detonation, and lower RPM with higher MP adds further to that risk.

Yes, a bit of carb heat will vaporize the fuel more quickly. You can see this on very cold days. As far as unfiltered air, there are so many beat-up, ill-sealed and cracked airboxes flying around that one is lucky if 80 or 90% of the air is getting filtered. Smoke particles are usually far smaller than the pores in the typical air filter, too.

Find the nearest boat and see if you can find its air cleaner/filter. Good luck.
 
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