CHTs

joe plihal · Post by **joe plihal** » Tue Jun 25, 2013 7:18 am

I have never been real happy with the CHT of my #2 cylinder. The engine is a 0-320, 150hp. I have tried to seal the baffles, used RTV etc. The other cylinder do not heat up in a climb as the #2 cly does. I need to climb at 105kts to keep it about 375 degrees. The #1 and #3 cylinders are the coolest at about 325 and the #4 is 340 in the climb. Once I get to altitude everything is fine with the temps all running about 325. I have trimmed down the baffle directly in front of the #2cyl a couple of times and I'm not sure that I didn't make it worse. I am considering trimming the aft portion of the bottom cowl to enlarge the exit area but I would like other folks input before I do that. Also, I normally fly into airports with little or no traffic and don't spend a bunch of time taxiing and idling. At a fly-in a few days ago I got stuck in a long line for departure and was distressed to see all 4 CHTs climb above 325 before I got to the runway. Any thoughts would be appreciated.
Joe

Post by **bullojm1** » Tue Jun 25, 2013 9:30 am

Hey Joe-

Have you calibrated your CHT sensor for your #2 cylinder? It might be worth a shot swapping the CHT probes between #2 and #4 to see if you have a CHT issue, or a sensor issue!

Try completely removing the dam in front of the #2 cylinder. I worked mine up using HVAC aluminum tape, from Home Depot. I have only about a 3/4" dam in front of my #1 and #2 cylinders.

Good luck!

joe plihal · Post by **joe plihal** » Wed Jun 26, 2013 1:46 pm

Mike
Thanks for the reply. I had swapped sensor leads earlier and that wasn't the problem. I have removed the baffle and will try that, Thanks Again!
Joe

Post by **Spike** » Wed Jun 26, 2013 3:20 pm

Which side is the oil cooler on and what are your oil temps?

John

captain_john · Post by **captain_john** » Wed Jun 26, 2013 3:44 pm

This is like an echo...

Last weekend up in Nova Scotia, Glen (a.k.a. Humptybump on VAF) was just telling me the same story about his 150hp RV-8!

He went on to talk about thinner fins on that (one?) cylinder and how it puzzles him too.

As I recall (perhaps it was Cessna) who specified that engine installed the oil cooler or something there originally and couldn't have the fins there. Obviously they needed to do something else for cooling that cylinder.

I would start by talking to Glen and noodling with him about how that engine (specifically THAT CYLINDER) originally got cooled.

My guess is that if it were my plane I would install a high pressure duct to blast onto the fattest fins of that jug.

Can you post up some pictures??

CJ

joe plihal · Post by **joe plihal** » Thu Jun 27, 2013 2:58 pm

John
The oil cooler is on the left side behind the #2 and #4 cylinders. The oil temp struggles to get to 180, I have never seen 200 on the hottest days.
Joe

captain_john · Post by **captain_john** » Thu Jun 27, 2013 8:37 pm

Yes, but you were talking about CHT's...

CJ

joe plihal · Post by **joe plihal** » Sun Jun 30, 2013 11:32 am

Flew the plane today with the baffle in frt of the #2 cly cut down to 1/2 inch.
The CHT was lower, I was happy until coming home from a breakfast the EGT on the #4 cly climbs to over 1500 degrees. Enrichening the mixture does almost nothing, pulling back the power did lower it to 1490. The CHT on that cyl was at 330, was in line with the rest of the clys and did not move.
I was close to my fuel stop so I started down and the #4EGT falls to stay in line with the rest. Everything seems fairly normal except the one EGT.
Took off for home and the EGT in question was down to 1430 and stayed there. I have a Dynon 120 and was wondering/hoping the problem might be a sensor.
Does anyone have any thoughts??
Thanks
Joe

Post by **Spike** » Tue Jul 02, 2013 11:18 am

What I was wondering is if the oil cooler is robbing too much airflow from the cylinders on that side. As they flow through the rear of the baffle to cool the oil cooler it is then not running past the cylinders. If the oil temp is low enough maybe try reducing airflow through the oil cooler and force more of it through the jugs?

John

hydroguy2 · Post by **hydroguy2** » Tue Jul 02, 2013 10:26 pm

joe plihal wrote:.....until coming home from a breakfast the EGT on the #4 cly climbs to over 1500 degrees. Enrichening the mixture does almost nothing, pulling back the power did lower it to 1490. The CHT on that cyl was at 330, was in line with the rest of the clys and did not move.
.....
Does anyone have any thoughts??
Thanks
Joe

I'll put my money on Bad probe or connection a EGT #4. did the engine feel or sound different?

If the CHT's were all tracking based on mixture or throttle setting they were most likely firing correctly.
I had #1 cylinder act strangely more than once, but always usually only after a fuel stop or long XC. Almost never acted up when the engine was cool. Last time I pulled the cowl I found the connection to the EGT wasn't shrink wrapped properly and occasionally contacted the motor mount. I believe this was causing a ground issue. Once I fixed that, I have had no problems with #1. I've also heard that the Dynon probes aren't the highest quality and failures are not uncommon.

joe plihal · Post by **joe plihal** » Wed Jul 03, 2013 8:01 am

Thanks for the replies...
John, since oil temp is not an issue at all I will try blocking a portion of the cooler and see what that does to the CHTs.
Brian, I found a poor crimp on the lead for the #4 EGT but have not flown it yet.
Thanks Again
Joe

captain_john · Post by **captain_john** » Wed Jul 03, 2013 8:38 am

Joe, what is your theory there???

Blocking the oil cooler to observe CHT's?

What is the expected outcome and what is the correlation?

CJ

Post by **Spike** » Wed Jul 03, 2013 8:41 am

Look up three posts CJ.

Spike

captain_john · Post by **captain_john** » Wed Jul 03, 2013 9:35 am

OH!

ok... I see it.

Hmmmm, I am interested in hearing how that works out.

I hope it does.

CJ

joe plihal · Post by **joe plihal** » Thu Jul 11, 2013 10:00 am

I blocked 1 inch at the top of the oil cooler and finally got to fly it yesterday. The oil temp did go to 182 and stayed there until I started down.
I can't say that the #4 CHT changed much at all. It was still running 340 after take off until I level off, in this case I went to 6500' and stay there. All in all I did gain in my #2 CHT issue, my EGT issue is fixed so I feel pretty good about this and I Thank You all for your input.
Joe