B

beberle

Active Member
Hello all,
I'm a new owner of a RV-6A and also a 1st time aircraft owner, so I've MUCH to learn!
I was base-lining engine performance on my bird w/ a Superior O-360 w/ 300hrs snew, carburated. Consistently, cylinders #1 & #2 running EGTs that are 120-150deg hotter than the back two. The CHTs are only slightly hotter.. only a 20-30deg spread between hottest and coldest.
Also, the front 2 EGTs are within 25-50deg of eachother and back two are about 20 apart.
Is this normal for a carbed engine? None of my rentals ever had this kind of instrumentation, so it's new to me :D I just don't like seeing #1 leaned out to 1430 while #3 is at 1290...

thanks,
Brian
 
EGTs are generally unusable from an absolute number basis. If the probe for one cylinder is 1/4" farther from the cylinder it will show a dramatically different temperature than the closer one. Next time you have the cowl off check the position of the probes.

EGTs are useful when leaning when used to find which cylinder peaks first, but the EGT number itself is pretty much meaningless.

CHTs are the temperature to pay attention to. If they are within 20 to 30 degrees you're doing fine. Most people preach to keep CHT's well below 400F.

Google "Pelican Perch" for a series of great articles on this. Other sources are the Electronics International Pilots diagnostic manual.

http://www.buy-ei.com/Information/Pilots%20Manual.pdf

And the GAMI engine articles
http://www.gami.com/articles/articles.php
 
Bubblehead has nailed it, the raw EGT value by itself is not always telling you anything specifically.

There is no good or bad number, unless it deviates from the normal at a given power.

For example, assuming you are used to seeing from new EGT numbers at takeoff, going through 1000' at full throttle and full rich, say, 1290, 1280,1305,1265 plus or minus variations on the day.

Then over time they change a little and one day you notice they are more like 1290,1280,1305 & 1425. What does this mean? Well depending if its an IO or O360, but given you have an O engine it will not be a partially plugged injector. You may also have noted a faster climbing CHT as well, suggesting that cylinder is running a less rich mixture. So what could cause that? Most likely to be an induction leak!

On the other hand you may see a rising EGT on C4 but a falling or lower CHT. What could that be? Two things, a plug failing and your mag checks were not done well enough.

I would be wanting to study the data files myself to see what trend I could see. Assuming that you have access to them.

At 300 hours it is possible to have inlet gaskets with cracks in them. Sadly not uncommon.
 
Well, I think I've found the culprit. The rear two EGT probes look like they've been installed about 1/2" lower from the exhaust collars than the front two. Looks like it should be simple enough to drill new holes to match the front two and weld in the old ones.
The EGT probes weren't lying AND the engine is running fine ;)
 
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