Help diagnose high EGT & high CHT

[skydvrboy]

I have one cylinder (#2) that is giving me high CHT's and EGT's when operating LOP.  This started the first flight after annual inspection and has progressively become worse.  Before when I would lean, all cylinders would peak in the following order 4-3-1-2 and the CHT's would drop to around 310-310-285-335 respectively.  During climb, ROP, the CHT's were around 390-350-320-375 respectively.  Other parameters: RPM 2500; MAP 24"; FF 8.0 GPM

After, when I go LOP the CHT's still peak in the same order, but cylinder #2 seems to stay at it's climb temperature.  For the first flight, climb CHT's were 385-355-320-370 respectively.  However once LOP, the CHT's were around 310-320-280-355. Other parameters: RPM 2500; MAP 25.5"; FF 8.7 GPM

On later flights it has progressively become worse, though admittedly the ambient OAT has climbed as well.  On one of my later flights I climbed to 9500' in search of cooler air (to no avail) and the LOP CHT's were around 340-360-310-390.   Other parameters: RPM 2500; MAP 21.5"; FF 8.0 GPM. 

When LOP Cylinder #2 always seems to be about 40 degrees warmer than the others.  Meanwhile EGT's on #2 are peaking around 1500 and I have always run about 5-10 degrees LOP after the last cylinder peaks.  Of note, on one low altitude flight, I set RPM at 2400 and MAP at 24" and #2 EGT peaked at 1550.  That is the only flight where that happened.

Now for my amateur incoherent ramblings... It seems that #2 is getting too much air and fuel and is peaking later and later.  In order to get the #2 CHT's to start dropping I have to lean so much that the engine is running rough.  This was never the case before.  In flight (and ground) mag checks show no issues, so I don't think it's a fouled plug.  I would think a partially clogged injector would cause that cylinder to get less fuel and run hot when ROP and peak sooner, which is the opposite of what I have going on.  Could an intake leak cause one cylinder to get too much air?  Is the exhaust valve sticking?  Any advice or other things I need to check out would be greatly appreciated. 

 

[47U]

2 hours ago, skydvrboy said:

I have one cylinder (#2) that is giving me high CHT's and EGT's when operating LOP.  This started the first flight after annual inspection and has progressively become worse.

What engine work did the shop do during the annual inspection?  What, if anything, changed?

[skydvrboy]

Not really any engine work done.  They fixed a cracked spark plug thread on cylinder #3; compression test; changed the oil and filter and cleaned the oil screen; cleaned the fuel screen; cleaned and gapped the spark plugs.  Basic stuff done at every annual.  Could have allowed some contamination to enter fuel, oil, or engine, but just as likely the timing could be completely coincidence.

[gabez]

reach out to savvy, don't do guess work. I learned my lesson 

[Oscar Avalle]

On 6/30/2025 at 11:55 AM, gabez said:

reach out to savvy, don't do guess work. I learned my lesson 

Agree share your data with Savvy they are great. Dont guess...

[PT20J]

Intake leaks cause noticeable roughness at idle and low power when the throttle plate is restricting airflow through the servo. Leaks don’t increase airflow much, if any, at WOT. 

If the engine is running smoothly it’s not a sticking valve. 

You can eliminate the injector nozzles by cleaning them. 

Since this happened after maintenance, I’d ask the shop what they did that might have caused this. But this only provides useful information if done soon after it leaves the shop. Memories fade. 

I always like to verify the instrumentation is accurate when I get an anomalous indication, especially if the engine is otherwise operating normally. I would swap CHT and EGT probes between cylinders 2 and 4 and see if the high temps stay with cylinder 2 or follow the probes. 

I might also check the condition of the probes and connections. 

[Will.iam]

If #2 is last to peak then it’s the closest to peak when running LOP and thus with more power equals higher heat so it will have higher cht. Gami injectors might help if the spread is greater than .5 difference between the first and last cyl peaking. You said tgey cleaned the injectors. They might have accidentally swapped #2 injector with a different cyl that is now giving more fuel to #2 than before. Might try swapping the cylinder that peaks first with the cylinder that peaks last to maybe balance out the fuel flow. Continental and lycoming do not balance their injectors as closely as gami does but even they can’t get it exactly the same. Only closer. 

[PT20J]

Precision Airmotive RSA nozzles are not available in different flow rates. However, it is possible to screw them up by swapping the removable restrictors between different bodies as they are a matched set. They should spray a steady stream about the diameter of a #2 pencil lead. If they spray a different pattern, you can try swapping around the restrictors between bodies and see if you can find a combination that produces steady streams in all four. 

[Shadrach]

A few things stick out here. 
 

1) your IO360 behaves differently than those I have flown. With few exceptions, EGT #3 typically peaks first and #2 peaks last. #3 CHT is usually the hottest or nearly the hottest.

2) Did you try a mag check at cruise power? 1550 is on the high side for a normally aspirated IO360. I would rule out an intermittent ignition issue first. I’ve had plugs that drop out at 2300rpm but perform normally during runup.

[AndreiC]

I am following this thread because my IO-360 behaves exactly like the OP’s. My #2 cylinder is the last to peak, and always has a significantly higher CHT than the others. (My CHT’s are quite low usually, in the 295-320 degrees range, except for the #2 which is always 30-40 degrees higher than the rest — closer to 350 in cruise, and on hot days reaching 375-380 in climb). 

For reference, my GAMI spread is very tight, probably 0.1-0.2 gph. But something odd is happening here as well. While leaning, cylinder 1,3 and 4 will peak at some fuel flow; and then I still have to move the mixture lever a while until the #2 peaks, but the fuel flow changes very little despite the EGTs still changing. For example, in cruise at 6500ft WOT, the fuel flow will stabilize around 9.4-9.3 gph while I do this mixture change, and cylinders 1, 3 and 4 will drop about 10-15 degrees EGT past peak until #2 peaks, but the FF remains unchanged. Actually, once #2 peaks it will actually drop below peak as well by about 10 degrees with no mixture movement. I usually enrich at this point until all cylinders are at peak, which again is not a discernible change in FF. All cylinder peak now at the same time when coming back from the lean side.

The behavior is as if the #2 EGT sensor has a time lag to decrease after peak from the rich side, even though all cylinders were behaving identically. I would have really thought this to be true, if it were not for the fact that the #2 CHT is always significantly higher. 

I’d love to have someone explain this behavior. 

[hazek]

If you don't post the data no one can really help you. As experienced by myself, witness accounts of what is happening in the air are unreliable. Then, data alone is not enough, you have to have all the data, the temps, the fuel flow, MP, RPM, everything. And then maybe you can figure something out.