Number 2 Cylinder hot across operating range. Ideas?

[wera710]

Need help on reducing CHT on the Number 2 cylinder (Front Left). I?ve read everything I could find on CHT issues on VAF but quite often the replies seem to gravitate to #3 Cyl or conversations about LOP v ROP. I?d like some advice strictly on how to reduce CHT in climb or in cruise on #2 on a standard Van?s cowl and baffling on the RV-8. The engine is a carbureted O-360A1D. CS prop. Bendix shower of sparks type mags. EDM-700 for CHT and EGT readings on all four cylinders. Nothing special or modified. In climb at 25 Square I am seeing CHTs on #2 as high as 415 to 420 deg. This is both at max performance type climbs or in cruise climbs with low angle and higher speed. Even throttled back ? still over 400. Other three cylinders all within a reasonably cool range during climb. Valves look great by the way?but still, I want this sucker cooled down.
I?ve checked the baffling and there are no glaring issues. It?s tight where it needs to be and the front of the cylinder vanes are not blocked off, although as others have noted, the vanes are pretty shallow.
More annoying is that in cruise, ROP operations keep the temps up in the 395+ range on that cylinder, while others drop as low as 335. Basically I have two cylinders that average 375 and one that is always low, around 335, and then number 2, which just won?t come down below 390 unless I lean to LOP.

Operating at 42 deg LOP in cruise, I can easily get #2 down to 373 to 385. But as soon as I go ROP its right back up to 395 or above. I don?t want to get into the LOP v ROP in carbureted engines debate, I just want to get this cylinder under control and close to the rest, temp wise, at ALL settings.
Any ideas would be much appreciated. Thanks.

[Mike S]

Two things come to mind at the moment---------first a bad sensor.

Second, and more likely is an intake leak on the one cylinder.

Good luck

[Bugsy]

Im no expert, just finished hr 25 of my phase 1. But my #2 is the coldest, I had to put a damm in front of it, my #4 is the warmest hovering around 400 with the oil cooler right behind it. But my temps make sense to me your temps dont make sense to me. Why would the cylinder closest to the cold air be the warmest if baffeling and induction system are operating normally. I'll watch this thread with interest.

[Toobuilder]

Some discussion about #2 (and #3) in this thread.

[wera710]

Mike, thanks for the link. I'd read most of the various posts but missed that one.

Bugsy, my thoughts were the same. Why would #2 be hottest? I've heard others have had the same issue as well. I have practically NO L channel in front of #2, so its getting all the air it can take at the inlet.

Mike S, I didn't give an intake leak a thought. So thanks for that! I'll also try swapping sensors to assure they are not the issue but I am pretty sure things are hooked up proper and operating correctly. I can get pretty good and relatively even temps in level flight (except for #1, which is always colder). But #2 just hates the climb phase.

Keep up the replies. This is all the result of a recently installed EDM-700 and man, seeing what I am seeing, I can't believe anyone willingly flies with out all four probes for CHT and four for EGT!! I equate flying without this data was like flying with head in sand. Which I've done for a decade! LOL.

[Neal@F14]

I'd also double check for an intake leak. Lycoming cylinder intake flange gaskets have a known reputation for leaking.

[humptybump]

Scott - a hot #2 is not uncommon. I had the same issue. I checked similar suggestions that have come here. Eventually I looked at the physical cylinder and baffling and made a mod based on DanH's notes.

click for my story

[wera710]

Sweet. Simple solution assuming no leak! Will try this next. Wish i had seen this over the weekend when I had the cowl off to check fittment!

[wera710]

May have found part of the problem. The gap between the front baffle (prop and ring gear baffle) was pretty large and not sealed. It had actually shifted, probably as a result of multiple removal and replacement of the cowl during painting. Talking a half inch gap, and close to 3/4 inch in one spot! I missed it because I was looking aft for issues. At a guess, it would seem like a large portion of air is getting dumped behind the prop and never pressurizing the number 2-4 side. Sealed it up today. Hopefully tomorrow will see a cooler #2 in climb.

[DanH]

Scott, it smells like an induction leak.

Do a mixture spread. Set up at 70-75% or so at perhaps 3000 feet, do big pull to someplace on the lean side of peak, then sneak up on peak from the backside. Write down the highest EGT you find for each cylinder, as each one peaks. As soon as they all peak, shove it full rich, let the EGTs stabilize, and record them. Subtract rich number from peak number for each.

If the hot one has very little spread, start looking for the leak.