EGT Differential

V

Vendata

Filing Flight Plan
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vendata
Hi

I just installed a new JPI 830 in my 67 Cessna 182 O-470R..
Im still getting everything dialed in , but noticed in cruise the EGT's on cylinders 1,3,5 were consistently higher than 2,4,6 - average by about 200-220 degrees..

On run up, prior to take off, I go into NRM mode, and EGTs' are pretty uniform.
EGTs are about 12-1300 on climb, which is normal..
CHT's are pretty consistent across all in the mid- lower 300's

The JPI manual states for carbureted engines the span should be 120-150 degrees differential as normal...


Any ideas ? Causes for concern?

Scott
 
Intake leak at the Y pipe? They're hard to locate but the evidence is there.
 
Stewartb said:
Intake leak at the Y pipe? They're hard to locate but the evidence is there.
Click to expand...
So if theres a leak there, that is leaning the mixture out at those settings, which is increasing the EGT, correct?

Thanks for that clue as to where to look. But that temperature differential is definitely not good, right?
 
I would be worried if there were significant Delta between cht's. If the engine is running smoothly and cht's are good, chill out. Many older egt gauges don't even bother with numerical markings.
 
You must have never had an 0-470 induction leak. That one side is 200*+ hotter than the other side is the stuff we install engine monitors for. The Y pipe rubber is likely sucking air on the hot side.
 
Then why are the cylinders all close to the same temperature if some are running leaner than others?
 
Are all the EGT probes equally spaced from the exhaust flange? I agree that delta is a bit high but aren't 470s also known for their inconsistent air/fuel ratios?
 
Check the position of where they drilled for the probes also..It's possible they are closer to the exhaust valves on the odd cylinders.
 
An O-470 induction rises from the carb and divides in two with a Y pipe. Each outlet ties into the respective side's induction with a rubber sleeve and two hose clamps. They loosen and leak. One side runs hot.
 
Awesome info with good places to look!. I helped install the JPI w/ my AP mechanic, we measured 2.5 inches down on all exhaust pipes is where we put our holes for the probes. Definitely going to re-measure and check those locations again though, and look at that rubber sleeve / hose clamp. Next up is oil change and will check it out then..
 
Ok so I checked out a few things during my oil change last week. There was a slightly loose clamp on the manifold hose under the #3 cylinder which I re-tightened.
Went for a flight yesterday up to Santa Ynez....Then down to Camarillo for some pattern work and back home..Here are the JPI logs...
What I noticed in Santa Ynez before the Camarillo run, was on the left side (246) some of the cooling sheet metal was tuned up, which could put cool air right don to the lower part of the engine. I was able to re-secure that and we went to CMA.. The EGT DIF was in line and peaking at about 150 degrees, on the way out it was as high as 200... Once in Camarillo during the take-offs I could hear some rattling, sounding like sheet metal..Once back at WHP, the sheet metal was back to the open position. I didnt monitor the DIF too much on the way back ... From CMA to WHP was a lower level cruise as well.. Ive attached screengrabs of the JPI log and a phot o of the sheet metal...Good flights both ways..
KIZA_KCMA_KWHP.PNG KWHP_KIZA.PNG KIZA_KCMA_KWHP.PNG KWHP_KIZA.PNG
 

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I don't see a problem with any of those temps, especially being carbureted. Seal the baffle metal with some red RTV and go fly.
 
200 is a lot.

To check for induction leaks while flying, try getting temps while at 2400 rpm and wot, then 17" and 2400. Induction leaks shouldn't make a huge difference at wot, but will accentuate the difference at low mp. Those two photos will tell you a lot.

You can also use the exhaust of a shop vac with a few PVC couplers and band clamp that to the carb heat tube, close up the main intake with a rag and some plastic, and pressurize the system. Then use soapy water spray and you will see bubbles where you have a leak.

The 470 is famous for running a wide range of temps, but 200 is too much. Some people advocate some carb heat for better atomization, others do a slight backing off of the throttle.

This is mine running with some carb heat.. The egt difference is at the bottom at 46*.MVIMG_20190407_110819.jpg
 
SloRoam said:
200 is a lot.

To check for induction leaks while flying, try getting temps while at 2400 rpm and wot, then 17" and 2400. Induction leaks shouldn't make a huge difference at wot, but will accentuate the difference at low mp. Those two photos will tell you a lot.

You can also use the exhaust of a shop vac with a few PVC couplers and band clamp that to the carb heat tube, close up the main intake with a rag and some plastic, and pressurize the system. Then use soapy water spray and you will see bubbles where you have a leak.

The 470 is famous for running a wide range of temps, but 200 is too much. Some people advocate some carb heat for better atomization, others do a slight backing off of the throttle.

This is mine running with some carb heat.. The egt difference is at the bottom at 46*.View attachment 73664
Click to expand...
 
SloRoam- Looking at the data, when I was in cruise (19"/2350) it had the most differential. On TO/climb and then in the pattern doing touch and goes, the spread was much less...Based on your comment, it would appear there may be a leak then, correct? (larger difference at lower mp).
Cylinder head temps have always been good. If there is a leak, what good is adding some carb heat?
I would think an intake manifold leak would be fairly serious, especially if it got worse while flying...
 
You should cruise at 19, then cruise at wide open throttle to be sure, but I would pop the cowl off and break out the shop vac.. It's easy to tighten the band clamps and you're allowed to do that as a pilot.

An induction leak isn't the end of the world...I am guessing many people fly around with them .. As long as temps are within range.
 
Thanks for all the info. I pulled the cowl, pressurized the intake system- found a small leak up front on the crossover tube on the left side, was able to fix by readjusting and tightening the clamp/hose.. everything else checked good. Took it out for a flight with no changes in the temps. I'm going to fly a few more days next week with it and monitor some more...
 
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