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Consistently Low #1 and 2 EGTs on an RV-4 O-360

MartinPred

Well Known Member
My #1 and 2 EGTs consitently run 80-150 degrees cooler than the other two cyclinders. Here's the data from a recent flight:

N402BD-fltdata.jpg


I'm running a Lycoming O-360-A1D carburated with a FP composite prop and Bendix mags. This is a factory re-man with about 400 hours on it. 72/74 compression on those two cylinders last time I checked.

As you can see, no temp oscillations and the CHTs are tracking with the other two cylinders (maybe a touch cooler due to air flow). And the engine runs like a champ. No roughness. Hardly no oil consumption, and tons of power. I've recently replaced the #2 probe so it's not that (plus it reads the same as the others when cold).

Is it just the placement of probes or do I have a couple of leaky valves?

-Matt
402BD
 
Standard RV-4 Cowling

Mike,

It's a pretty standard RV-4 cowling. There's a slight bump where the lower cowling meeting the baffling. But how would that affect EGTs?

-Matt
402BD
 
Not the cowling, the baffling --------piece of alum sheet sticking up in front of the cylinder fins.

It is there to prevent too much air from being forced into the two front cylinder fins.

Here is a random photo of the air dam I found as an example.

2012-07-04_15-38-52_41.jpg
 
Huh.

I see. Nope. Nothing like that.

Would you need something like that if you're CHTs were too low?

Thanks,

-Matt
402BD
 
EGT vs CHT

Not the cowling, the baffling --------piece of alum sheet sticking up in front of the cylinder fins.

It is there to prevent too much air from being forced into the two front cylinder fins.

Mike, I can see an air dam like the helping to balance CHTs, but the OP is referring to EGTs. From a quick look at the data it appears his CHTs are pretty evenly matched. Would an air dam also help with EGT?

I'm curious as tobl what people think because have a similar problem on my 0-360 A1A. #2 EGT is consitently 200 degrees lower than the others. I've checked the probes and it's not a probe problem.
 
Mike, I can see an air dam like the helping to balance CHTs, but the OP is referring to EGTs.

:eek: sorry, my bad------------switched to decaff coffee.........

Disregard my meaningless stuff above.

Have you tried pulling a small bit of carb heat to see if that will even out the temps??
 
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EGT probe placement

Look to see if the EGT probes are all equal spaced? Also check for exhaust leaks in those low cylinders? And finally look for intake leaks leading to the cylinders?

Dos Centavos
 
I'll check it out

I usually run with a little bit of carb heat. I'll play around with it next time I go flying and see if that makes a difference.

I've been thinking it might be a leaky exhaust valve. I'm almost due for my annual so I'll poke around with the borescope and see how it looks.

Thanks!

-Matt
 
It's normal to have a fairly large EGT spread with a carburetor. Especially front to rear. If you want to improve the spread you can apply a little carb heat(improves fuel vaporization), move the throttle plate slightly which can bias the air flow front to rear on a four cylinder engines,or change the discharge nozzle to one that atomizes better(like the one we use in our 340). A combination of all of the above will only improve the spread a little. The single best way to have balanced EGT's is to change to fuel injection.
From your description of your engine and the data displays it looks to me like you have a normal healthy carbureted engine, with normal EGT spreads. Don't worry be happy!
 
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