C172M 180hp AirPlains conversion runs HOT

  • JOSE LOPEZ DEL PUERTO
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3 years 5 months ago #1237 by JOSE LOPEZ DEL PUERTO
Replied by JOSE LOPEZ DEL PUERTO on topic C172M 180hp AirPlains conversion runs HOT
If air cooling is right and magnetos timing is right, the cause could be insufficient fuel flow. Some times carburetors need to be tweaked.

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3 years 5 months ago #1236 by GARY PALMER
Replied by GARY PALMER on topic C172M 180hp AirPlains conversion runs HOT
Given your earlier comment, we know your oil cooler is mounted on the firewall? And there is a scat tube (probably 3 inch) which connects from the baffle to the oil cooler. Where do you have the opening in the baffle which you closed. Mine is in the upper corner behind the #3 cylinder, is that where yours is too?

I am amazed that by covering the oil cooler air intake you actually saw cooler temps. Was that due to the cooler daytime temp or the better airflow over the 1 and 2 cylinders.

If you are in an experimenting state of mind, I was thinking about a small curved baffle mounted on the upper cowling which diverts some air flow down between the cylinders. I just have a few problems trying this: 1) I am NOT an A&P and unable to craft such an appliance, and 2) I am not an A&P and regardless of what i learn I am not sure I could do anything since the plane is certified.
But you bring an interesting question, would #1 and 3 be cooler with better air flow versus a diversion of air to the scat tub and oil cooler.

So I am thinking there is another approach (have I said I am NOT and A&P?). Instead of mounting our oil coolers on the firewall, what about a baffle mount? It would force more air flow to remain inside the baffle compartment and would still give good airflow over the oil cooler. Anyone have insight on that approach?

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  • Martin Fass
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3 years 5 months ago #1235 by Martin Fass
Replied by Martin Fass on topic C172M 180hp AirPlains conversion runs HOT
Update: I temporarily covered the opening in the rear baffling leading to the oil cooler. Did this on a cool day and for one lap of the pattern. The temps on the right side were about 35 degrees cooler than before, so I think the answer has to involve moving the air intake for the oil cooler away from the current position in the baffling. Not sure about specifics, wondering if there's a field approval out there, or anyone who's done this?

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3 years 5 months ago #1218 by Martin Fass
Replied by Martin Fass on topic C172M 180hp AirPlains conversion runs HOT
Interesting thoughts. Thanks!

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3 years 5 months ago #1216 by STEVE ELLS
Replied by STEVE ELLS on topic C172M 180hp AirPlains conversion runs HOT
One way to check for induction system leakage is to connect the "blow" side of a very clean shop vacuum to the carb air box and pressurize the system with the shop vac while applying soapy water to the induction system connections. Bubbles should form at any leaks.
It does take some back woods engineering (cardboard, duct tape, etc.) to connect the vacuum to the air box but it's an inexpensive system.
Remember that it's critical to blow only clean air into the system.
Since both of you guys are reporting higher temps on #1 and #3 is seems likely that the problem is airflow since 1 and 3 are both on the copilot's side of the engine, and since Air Plains has developed a fix.
I also have a O-360 in my Comanche and see the same thing. But I'm not seeing as high a numbers as you.
I once read an obscure article that said running a fine round file down between the cooling fins on the top end of the cylinder to clean out the casting flashings lowered CHTs. You might give that a try.

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3 years 5 months ago #1210 by Martin Fass
Replied by Martin Fass on topic C172M 180hp AirPlains conversion runs HOT
Good input, thanks. I've replaced the scat tube as well. I agree bigger oil cooler won't change much. I have the bayonet probes and have heard the same about spark plug ring probes. I've noticed that high baffle in front of #1 as well, AirPlains never told me about a mod to the front baffle, though they have one to the back baffle -- I'll have to aske them about that, makes sense that lowering it could help. Fuel flow in climb is 15+ so I think the mixture is good, but I like your suggestion to look for intake (or exhaust?) leak. We've got the baffling tweaked as well as possible.
Again I appreciate the quick and detailed response. Will post if we find a solution!

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