Odd EGT temp readings

alcladrv · #1 02-12-2007, 08:11 PM

I fly an RV-7A with a carbureted ECI O-360 and fixed pitch prop. On a trip last night, OAT averaged -5F at 4500 feet. EGTs varied from 1290 on the left front cylinder to 1415 on the other 3. Sorry, I can't remember the cylinder numbers as I type this.

After 2 1/2 hours of normal enroute temps and operation, I reduced power to start the descent and the right front cylinder EGT just started to skyrocket. I then went to full carb heat on and the EGT lowered to its previous range. Of course, I enriched the mixture as I descended.

I tried it 2 more times. Each time I closed the carb heat, the right front cylinder EGT started to skyrocket. Each time I select full carb heat on the EGT came down.

The plane, engine/prop combination has a 180 hrs. on it over the past year and a half.

Has anybody seen this before? Any ideas of things to check out?

Thanks, Mike

664781 · #2 02-13-2007, 10:40 AM

Mike,
Swap out your EGT probe and wires, if they are long enough, from the front cyl to the aft cyl. This will tell you if the problem stays with the cyl or the EGT system. If it is an indication problem then just swap probes to see if it is a bad probe or wireing. If it is staying with the cyl. I would look at the intake tubes for the bad cyl.

Hope this helps.

mahlon_r · #3 02-13-2007, 10:53 AM

Maybe an intake leak on that Cylinder?
Good Luck,
Mahlon

Low Pass · #4 02-13-2007, 11:46 AM

Quote:

Originally Posted by mahlon_r

Maybe an intake leak on that Cylinder?
Good Luck,
Mahlon

This is a good and significant point. Follow up on it. I know someone who burned up a cylinder (valve & seat) in this situation.

collinsj57@adelphia.net · #5 02-13-2007, 04:28 PM

When you open your carb heat you no longer have ram air feeding the carb. I suspect the air flow changes dramatically and as you most likely know carbs are known for poor fuel distribution. I see large differences in EGT between WOT and any other setting. The throttle plate changes the distribution as it move from full vertical to any horizontal setting. Not saying you should not check for air leaks but poor distribution is a fact of life with a carb.

alcladrv · #6 02-14-2007, 08:45 PM

Thanks for the input. I'll try swapping the EGT probes.

Why would an intake leak suddenly develop after 2-1/2 hours of normal operation? It would really help to get a starting point to begin the trouble-shooting process.

Thanks, Mike

mahlon_r · #7 02-16-2007, 09:33 AM

Maybe you sucked a gasket or a hose clamp loosened up? The intake leak will show up at lower power more then at higher power, so when you reduced power, maybe you had it all along but just noticed it. Sorry for the delayed response. I am away and have very limited internet access.
Mahlon