Engine Runs Hot-Need Suggestions

[mvivion]

Okay, this is a modified Cessna 175, converted to tailwheel, with an Avcon engine installation of an Lycoming O-360 A1A, constant speed prop. A JPI 900 engine analyzer is installed.

This engine's cylinders have always run pretty hot, but it seems to be getting worse. Enroute across Montana last weekend, CHTs were running 410 to 415, except for number 3 which runs a bit cooler. That is leaned till it pops, then richened considerably, at 2350 rpm and 20 to 21 inches of MP, and 9.7 to 9.8 gallons per hour. In my experience with these engines, that's a pretty conservative fuel flow for that power setting.

I've done a good bit of work on baffle seals, and they're pretty tight now. Looking into the top deck with a flashlight on the ground, they pretty much show few if any leaks, certainly no significant ones.

I spoke to a good friend who flys a lot of these engines, and noted that in his experience, the JPI instruments read about 20 degrees high on average. If that's true (and next time I fly we're going to check those temps with an IR gun), that would imply CHTs are below 400.

I've flown a lot of 360s, including several on AvCon converted Cessnas, and never seen these high temps. Interestingly, these temps are pretty consistent as well, as in regularly, and consistent between cylinders.

And, summer temperatures aren't even above 80 yet....

Any thoughts on where we should look?

MTV

 

[OLDCROWE]

Take a flight and keep it running hard, land where you can shut down rapidly and have someone standing by with your IR gun to get readings immediately after shutdown and compare with what you note at shutdown.

 

[skywagon8a]

Are your CHT probes in the cylinder well or under the spark plugs? And where were they mounted on those other AvCon converted Cessnas? I like to see CHTs below 400.

 

[mvivion]

Are your CHT probes in the cylinder well or under the spark plugs? And where were they mounted on those other AvCon converted Cessnas? I like to see CHTs below 400.

If by "under the spark plugs" you mean gasket type senders, no, these are the bayonet type, mounted in the appropriate fittings in the cylinders. And, all the other O-360s I've flown with full engine monitors had the same type "probes".

And, I totally agree on the 400 degree mark. Which is why I'm trying to figure this out. Every other O-360 I've run had CHTs well below these.

MTV

 

[cubdriver2]

Tool tim Tim had that same problem a few years back and I think it was Larry Vetterman that told him it probably was running to lean. Drilled out the main jet one size bigger and it cooled down

Glenn

 

[skywagon8a]

Is the spread between ambient and CHT expanding or is the increase due to warmer ambient temps? Is there a possibility the piston rings are too tight? If the end gaps are minimum there is the possibility of increased friction on the cylinder walls causing high CHTs.

Are your baffle seals long enough to lay over the cowl rather than just closing the gaps? When they lay over as shown here, the air pressure tightens the seal. I lowered the temps on my 185 by changing to this type of seal. The seals should always face the cooling air.

Your fuel flows seem generous for the power setting.

 

[stewartb]

If you have >200° leaning authority I wouldn’t think fuel. Less than 200° I’d increase flow. I fought the same thing for years in my Cessna. Fuel was the solution.

 

[cubdrvr]

Remove CHT gauge.

 

[Bill Rusk]

You might double check your timing. Heavily advanced timing will cause the engine to run hot.


Bill

 

[DENNY]

If this is a new issue I would look at Timing especially with Slick or Electronic mags. A advanced right mag won't effect starting but will create a CHT issue. Primer line leak check on the inside bends I had a buddy with a rebuilt 0360 that chased Hot cylinders over 400 for two years # two was the hottest even full rich. He pulled the jug and had intake /exhaust valves redone, drilled out main jet, every baffle mod you could think of. Finally found a hole in the inside of the SS primer line where it went around #3. Do a positive pressure leak test on the intake. Does the cowl have some strange intake or exhaust that is building pressure in the lower cowl? Did someone pull the plug for a carb temp gauge and not put a probe in? Is this your plane? If it is a buddys plane I would double check everything yourself because people may not understand what it means if you said "did you check" so they basically lie to you. If it is your plane I would double check everything again because the the only one that lies worse than your buddy is usually yourself!!:lol::lol:
DENNY

 

[hotrod180]

Curious what the CHT limits for the Lycoming 360 and/or Avcon conversion are?
FWIW the CHT limits for the Continental 470 are called out in the engine TCDS.
They are 50 to 75 degrees higher for spark plug gasket probes than for bayonet probes, depending on which model 470.

 

[mvivion]

Curious what the CHT limits for the Lycoming 360 and/or Avcon conversion are?
FWIW the CHT limits for the Continental 470 are called out in the engine TCDS.
They are 50 to 75 degrees higher for spark plug gasket probes than for bayonet probes, depending on which model 470.

The CHT limit for the O-360 A1A is 500. Lycoming and most “experts” on these engines recommend running at or below 400.

MTV

 

[stewartb]

Given how hot rod mufflers reduce CHTs on Cubs, it may warrant inspecting your exhaust to assure it breathes easily.

I have zero knowledge of Lycoming installations in a Cessna cowl but I think the first thing I’d try in that cowl would be a cooling lip.

 

[mvivion]

Given how hot rod mufflers reduce CHTs on Cubs, it may warrant inspecting your exhaust to assure it breathes easily.

I have zero knowledge of Lycoming installations in a Cessna cowl but I think the first thing I’d try in that cowl would be a cooling lip.

Already has a small cooling lip. May need to make a bigger one, but…. Power flow exhaust installed.

MTV

 

[stewartb]

Most guys (including me) usually think increasing airflow through the cylinders is the key to CHT management. Mike Skup always focused on air transfer speed. He wanted to maximize heat transfer, and his theory is that faster/more isn’t always the best approach. But, my 180 runs cooler with cowl flaps open in cruise, so? We’ve all read about measuring the top deck pressure to calculate the differential. That may be a worthwhile exercise.

To the fuel thing, my Cessna benefitted greatly from increasing fuel flow at takeoff-initial climb. I lean in cruise to the same flow that I used when it ran hot. In my plane, once it got hot at the beginning, it stayed hot. Once I had the fuel to keep the initial flight phases cool, my cruise temps remained lower. That was a very happy change after over a decade of fighting mildly high temps.

 

[gpepperd]

I would go with Bill and Denny on the timing. Cured several hot engine problems by small adjustment to timing.

 

[BC12D-4-85]

I like the EGT margin comment - full rich to peak #'s by cylinder. Timing also. Carbs can build up internal debris so make sure it's clean.

Gary

 

[DENNY]

Curious what the CHT limits for the Lycoming 360 and/or Avcon conversion are?
FWIW the CHT limits for the Continental 470 are called out in the engine TCDS.
They are 50 to 75 degrees higher for spark plug gasket probes than for bayonet probes, depending on which model 470.

Lycoming continues to say Max CHT limit is 500 degrees despite issues with some engines and need for "Wet Head cylinders that sprayed oil on the exhaust valves to prevent early failure. This also a contributing factor for the "Wobble Test" early exhaust valve guide wear. They also put out a SB recommending keeping CHT below 400 degrees for maximum service life. I asked a factory rep at a trade show if they actually ran an engine to TBO with a constant CHT temp of 500 degrees and he admitted they never did and would only reach that temp for a short time before backing down. I have seen poorly designed experimental builds and highly modded aircraft that always run well over 400 degrees with the excuse that Lycoming says it is within limits. Not heard of a lot of reports of them making 2,000 hr TBO for some strange reason. https://www.lycoming.com/sites/default/files/attachments/Fuel%20Mixture%20Leaning%20Procedures.pdf See what they recommend for maximum service life. My CHT rant for the day.
DENNY

 

[mvivion]

I would go with Bill and Denny on the timing. Cured several hot engine problems by small adjustment to timing.

Agreed. It’s going to take some research. As I said, these are modified Slick mags, converted to electronic ignition. Neither I nor the mechanics here know diddly about these mags, and the company went out of business quite a while back. LASAR is the brand, I believe.

I think first test will be to turn the electronics off (there is a cockpit switch for that purpose….go figure) and see if that changes anything. Setting these mags requires an electronic box, which I bought from the previous owner’s (he who installed these things) mechanic.

Stewart, I totally agree on air flow. I’m trying to visualize a bigger lip…. I installed an exhaust pipe fairing which is supposed to increase differential. Not sure it helped.

MTV

 

[wireweinie]

Agreed. It’s going to take some research. As I said, these are modified Slick mags, converted to electronic ignition. Neither I nor the mechanics here know diddly about these mags, and the company went out of business quite a while back. LASAR is the brand, I believe.

I think first test will be to turn the electronics off (there is a cockpit switch for that purpose….go figure) and see if that changes anything. Setting these mags requires an electronic box, which I bought from the previous owner’s (he who installed these things) mechanic.

Stewart, I totally agree on air flow. I’m trying to visualize a bigger lip…. I installed an exhaust pipe fairing which is supposed to increase differential. Not sure it helped.

MTV

To set LASARs, they first require base timing setting. They are, in effect, a slick mag with electronics installed. After base time is set, then a special test box is connected to check for the electronic time.

I have the test box if you need it but I'll need to find any manuals to go with it.

Web

 

[mvivion]

To set LASARs, they first require base timing setting. They are, in effect, a slick mag with electronics installed. After base time is set, then a special test box is connected to check for the electronic time.

I have the test box if you need it but I'll need to find any manuals to go with it.

Web

I havethetest box, and instructions. Question is whether they were set right.

MTV

 

[BC12D-4-85]

...This engine's cylinders have always run pretty hot, but it seems to be getting worse. Enroute across Montana last weekend, CHTs were running 410 to 415, except for number 3 which runs a bit cooler...
MTV

Setting mechanical or calibration issues aside for a minute, I'd find it hard to claim a change for the worse unless the density altitude, power level, leaning degree, and true airspeed were kept similar for comparison.

Gary

 

[akmarty]

How are the temps at full rich? My o360 has the 4064-1 carb because the jets are bigger than the other (3878 I think) carb.


Sent from my iPhone using SuperCub.Org

 

[aflyer]

I started with LASAR mags on my RV8 in '03, and I had overheating problems. They have a very aggressive advance curve. After all the usual baffle etc. changes, I switched to Lightspeed and my troubles went away.

 

[skywagon8a]

I havethetest box, and instructions. Question is whether they were set right.

MTV

Agreed. It’s going to take some research. As I said, these are modified Slick mags, converted to electronic ignition. Neither I nor the mechanics here know diddly about these mags, and the company went out of business quite a while back. LASAR is the brand, I believe.

I think first test will be to turn the electronics off (there is a cockpit switch for that purpose….go figure) and see if that changes anything. Setting these mags requires an electronic box, which I bought from the previous owner’s (he who installed these things) mechanic.

Stewart, I totally agree on air flow. I’m trying to visualize a bigger lip…. I installed an exhaust pipe fairing which is supposed to increase differential. Not sure it helped.

MTV

I started with LASAR mags on my RV8 in '03, and I had overheating problems. They have a very aggressive advance curve. After all the usual baffle etc. changes, I switched to Lightspeed and my troubles went away.

This is an excellent clue Mike. Can you totally disable the Lasar system and revert to just magnetos without too much difficulty for a test?

 

[mvivion]

Setting mechanical or calibration issues aside for a minute, I'd find it hard to claim a change for the worse unless the density altitude, power level, leaning degree, and true airspeed were kept similar for comparison.

Gary

Gary, that’s the point. The only one of those things that I haven’t kept constant is DA, and it’s been lower, which is what got me going on this.

MTV

 

[mvivion]

I started with LASAR mags on my RV8 in '03, and I had overheating problems. They have a very aggressive advance curve. After all the usual baffle etc. changes, I switched to Lightspeed and my troubles went away.

That is interesting, and the first real feedback I’ve heard on the LASARs. Point taken.

Mtv

 

[mvivion]

This is an excellent clue Mike. Can you totally disable the Lasar system and revert to just magnetos without too much difficulty for a test?

That I don’t know. I’ve been wanting to get to the airport and read the materials that have on them…..installation, timing, etc. Time for that for sure.

MTV

 

[stewartb]

Do you have the Laser controller box that uses MP to vary timing? This article says it advances timing up to 42°. That could definitely heat things up.

https://www.avweb.com/ownership/hot-stuff-unisons-lasar-ignition-system-part-one/

 

[wireweinie]

That I don’t know. I’ve been wanting to get to the airport and read the materials that have on them…..installation, timing, etc. Time for that for sure.

MTV

Pull the circuit breaker that powers the brain box. Everything reverts to standard magneto functions.

Web