What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

O-360 EGTs cool with carb heat

no7rosman

Active Member
Hello,

I recently did some maintenance on my plane which appears to have caused a problem. The maintenance was an oil change and clean and re-oil the air filter. (I know...what could go wrong) I have done a few oil changes problem free...but this was the first time I cleaned and re-oiled the air filter on this plane. It's a 9A.

Now I am unable to lean to the customary gph. The EGT on 1 & 2 are at 1400-1500 while gph are 10-11. Prior to this maintenance #1 would be the hottest at about 1300 and I'd be burning about 7.5-8 gph.

Steps:
1. Level out around 7500 ft
2. Start Leaning
3. The EGT's for 1 and 2 rapidly increase to around 1400-1500 while gph is around 10-12
4. EGT's for 3 & 4 are normal around 1100-1200
5. Turn on the carb heat and everything goes back to normal

The high EGT's come down immediately when the carb heat comes on. While the carb heat is on, I am able to lean to the normal gph of 7-8 with approximately 1200-1300 on the EGT.

Does this sound familiar to anyone?
 
Last edited:
So you cleaned the air filter and now the engine is getting more air. More air and it can use more fuel. This means you will have to lean a lot more to go LOP. Turn on carb heat and the engine gets less pounds-mass of air so now you have an even more ROP mixture and EGTs go down.

Go fly and lean to LOP and let us know what fuel flow you have at that point. Here EGT value is not the most important element. Knowing fuel flow at LOP is.

Carl
 
Thanks guys. My friend who was in the plane with me and an A&P said the same thing about the filter having too much oil. It's possible and I plan on cleaning it again maybe not put any oil on it.

WRT Carl's response...I don't really like my EGT's above 1500. Especially when it's only 2 cylinders. I'll go a little higher and see how it goes.
 
No filter

Maybe try a test flight without any filter at all and see if the filter is actually playing any part in the equation or if you should be looking at something else.

Mark
 
Thanks guys. My friend who was in the plane with me and an A&P said the same thing about the filter having too much oil. It's possible and I plan on cleaning it again maybe not put any oil on it.

WRT Carl's response...I don't really like my EGT's above 1500. Especially when it's only 2 cylinders. I'll go a little higher and see how it goes.

Just how dirty (clogged) was your air filter?

Excessive air filter oil would, if anything, restrict air flow not increase it. This would result in the opposite of what you observed. More likely excess oil would just drain and collect in the air box.

I note Lycoming does not have an EGT limit on normally aspirated engines. On your 1500 reading, the reading itself is very dependent on where you placed the probe. There are reams of threads on understanding EGT absolute value as compared to peak EGT. I recommend you take a look at the Mike Busch material on the subject, like this one: https://www.savvyanalysis.com/articles/egt-myths-debunked

Never clean a K&N filter without applying new oil.

Carl
 
Thanks guys. My friend who was in the plane with me and an A&P said the same thing about the filter having too much oil. It's possible and I plan on cleaning it again maybe not put any oil on it.

WRT Carl's response...I don't really like my EGT's above 1500. Especially when it's only 2 cylinders. I'll go a little higher and see how it goes.

It only takes a tiny amount of oil - just a little line of it along each crease on the outside. It might initially only be a little red line 1/8" wide. Give it an hour or two and it will disperse throughout. Be sure the filter has completely dried post-cleaning before adding the oil.
 
Thanks for the help everyone. I'll give these suggestions a try and report back.

Carl - I have read lots of information on the subject of EGT's. The part that makes me twitch is how fast the temps climb, the fact that it's only 2 cylinders, and it wasn't happening pre-maintenance. I will give your recommendation a try and see what happens.
 
Back
Top