High CHT Temp

[Beach Bum]

We have the paperwork settled and started flying the Super Cub but have found it difficult to keep the CHT's under 410 F. Even just taxiing to the runway the temps go into the 330 range. At 2600 RPM we're talking 430 and 440. Info on plane is:

New shop overhaul 0-320
Chrome cyl
New EI CHT gauge and probe
Temperature verified with laser
Rear oil cooler
8241 prop
New baffling
Oil pressure at 55 psi in cruise
Mineral oil for break-in
6 hrs since overhaul
Carb mixture hits the full rich stop
Oil temp is 215 - 220
Timing double checked
Discussed with IA but no joy

Ideas appreciated...

[Steve's Aircraft (Steve)]

A similar situation once turned out to be a engine breather vent line plugged.

Steve

[Tim]

Try running at 2400 and lean of peak, just on the edge of roughness.( or even a little rough ) It may take a few minutes for the temp. to come down, but it will. A new engine is tight and will always run a little hot, once you have a little time on the engine the temps should come down. Your mileage may vary.

[aviationinfo]

BB, that oil pressure in cruise seems low to me. My manual says minimum normal operating pressure is 60 psi. Not saying it's starved for oil and that's what's causing your CHTs, but did want to note that. I also note that for an O-320 your oil temp is a bit on the highish side for this time of year. (I assume the OAT is below 70 degrees where you are?)

As an example, and I'm not saying this is how every engine should read--- my oil pressure in cruise on a very hot day after hours of operating is 65-70 psi and the oil temp is 195-200. YMMV. Yours is a new engine and I'd expect it to run warm during break-in but the oil pressure shouldn't be lower than the normal range, should it?

[aviationinfo]

He's supposed to run it fairly hard during the break-in though, isn't he? And I should add that mine has steel cylinders so the comparison might not be straight across.

[cruiser]

Chrome rings? Hope not. Jim

[skywagon8a]

Double check your baffles. Did you forget to install the intercylinder baffles? They are hard to see. Make sure that there are not any big spaces for air to leak around the engine rather than to go by the fins. I agree that the oil pressure sounds low for a Lycoming unless it is the high temperature which is causing it.

[Wingwrench]

Have you checked the mag timing?

[Beach Bum]

It doesn't take much of a pull on the mixture knob before it goes lean. Say 3/4 to 1" pull for the engine to run rough. I thought it was set up too lean on the linkage but the mixture arm goes stop to stop.

Try running at 2400 and lean of peak, just on the edge of roughness.( or even a little rough ) It may take a few minutes for the temp. to come down, but it will. A new engine is tight and will always run a little hot, once you have a little time on the engine the temps should come down. Your mileage may vary.

[Beach Bum]

Some good input here. Someone else mentioned this was low. I'll add washers to boost the pressure.

BB, that oil pressure in cruise seems low to me. My manual says minimum normal operating pressure is 60 psi. Not saying it's starved for oil and that's what's causing your CHTs, but did want to note that. I also note that for an O-320 your oil temp is a bit on the highish side for this time of year. (I assume the OAT is below 70 degrees where you are?)

As an example, and I'm not saying this is how every engine should read--- my oil pressure in cruise on a very hot day after hours of operating is 65-70 psi and the oil temp is 195-200. YMMV. Yours is a new engine and I'd expect it to run warm during break-in but the oil pressure shouldn't be lower than the normal range, should it?

[Beach Bum]

It's my understanding that sustained flight in the 70 - 75% power range is desirable for break-in. Anyone know the temperature drop I can expect after break-in? 20-30 degrees?

He's supposed to run it fairly hard during the break-in though, isn't he? And I should add that mine has steel cylinders so the comparison might not be straight across.

[Tim]

It doesn't take much of a pull on the mixture knob before it goes lean. Say 3/4 to 1" pull for the engine to run rough. I thought it was set up too lean on the linkage but the mixture arm goes stop to stop.

If that's the case, it's not rich enough at full rich position. This may or may not pertain to your engine. My 0-320 with 9.5 to 1 pistons wasn't getting enough fuel at full rich to run cool enough at full throttle when in climb. After much research I drilled out the main jet in the carb. Problem solved

Tim

[Dave Prizio]

You should be breaking in your engine at 65-75% power with no temperatures outside of the factory-recommended temperature ranges. Running at reduced power and/or LOP should not be necessary and is not advised.

Did you overhaul mags when you did the engine? Have you checked the timing? Internal and external timing need to be spot on to eliminate those possible sources of trouble. You don't mention electronic ignition, so I assume you don't have it. If you do I have seen many people have high CHTs caused by too much advance in their electronic ignition systems.

Baffles must be installed properly with no gaps. New baffles make me wonder if this is a possible problem. As mentioned intercylinder baffles must be properly installed.

Your mechanic should be able to easily boost oil pressure by adjusting the oil pressure relief valve. Be sure to check the valve seat to make sure it is in good shape and sealing properly. If he still can't get the oil pressure to come up to the 70-80 psi range you most likely have an internal engine problem.

If you have an old oil cooler you may need to have it flushed out and overhauled (not something most mechanics can do).

My theory is that if you are unsure of where the problem lies, always start with the stuff that is cheap and easy -- baffles, mags, oil pressure relief valve, oil cooler. After that it is going to get ugly pretty quickly. It is a bad sign when a freshly overhauled engine has these problems. Hopefully you can find some inexpensive solutions that will calm those initial concerns.

Dave Prizio

[Dave Calkins]

...what Dave Prizio said...

Also, Tim, LOP ops. for break in?? (i don' thin dat a good idea)

[sierra bravo]

Given a new installation probably has good baffles and the timing has already been verified correct, I'd look at the carb. Lean is the rule with every new and rebuilt carb I've ever installed. Float settings need to be checked as well. Next I'd look at the exhaust. My own engine saw 35* plus CHT reductions by changing a perfect stock muffler for a Hot Rod muffler. That was an eye opener.

[Tim]

Dave I didn't mean for him to break his engine in lean of peak, just as a test to see if he could get the temps to come down. I think his engine is running to lean ( at full rich position on the red knob ) by what he said about where the mixture is when it starts to get rough.

[mvivion]

Where did the engine come from? I flew a Cub that had had an engine from a Twin Comanche on it. Ran hot. Mechanics finally figured out that the installer hadn't properly converted the engine for fixed pitch prop. Fixed that and it ran fine. Two airplanes came from the same rebuilder, and both had those engines and those problems.

MTV

[Dave Calkins]

Tim, my misunderstanding.

Also, not that it's happening, but.....has every normal item been checked methodically? I've seen folks not be methodical and chase issues they really wouldn't have had if step by step checking had taken place with no assumptions.

I, too, have had many lean carburetors with rebuilt engines. I no longer send the carbs out. .....been screwed too many times by thinking "newer is better". D

[Roger Peterson]

Sburg58 just had the same thing happen on his PA18 95. Muffler baffle had broke loose and plugged the exhaust. Ran to 400 on real cool days.

[DW]

Doesn't seem like enough prop for brake in on a new engine but more pitch will mean more heat.

[Indabush]

What carb are you using? My old motor had the same problem but was due to them installing the wrong nozzle in the carb (high cht's) and wrong main bearings. (low oil pressure)

[fobjob]

Nothing drastically wrong with mine when I started to cool it. It was 390+OAT=CHT.....What is your OAT when you are measuring those numbers?

[Beach Bum]

about 72 today.

Things we're planning to check:

Verify carburator
Flush oil cooler
Check oil screen for bad news
?

Nothing drastically wrong with mine when I started to cool it. It was 390+OAT=CHT.....What is your OAT when you are measuring those numbers?

[irishfield]

Oil cooler should have been flushed or replaced before first engine run. Can't see it having anything to do with high CHT immediately after start up or the oil pressure.

Are you seeing high oil temps as well?? Was the case half seam dressed and the crank / cam journals line bored?.. and they forgot to counterbore the crank bearing retainer pin holes.. that are now working as brakes? Seen it happen once... out of ECI...

[mike mcs repair]

likes been said a couple times in here, but not addressed?, checking INTERNAL mag timing.... not the mag to engine timing... see if they were assembled right..

[fobjob]

Are both rear cylinders showing about the same temp, and the front ones less?

[skywagon8a]

After you double check the mag timing, your extremely high CHTs are your starting point. The high CHTs are likely the cause of the high oil temp and that is likely the cause of the low oil pressure. Those over 400 degree CHTs are the source. A high CHT would be 100 degrees cooler than your numbers. What did you find on your inter-cylinder baffles? Those are the ones which come from Lycoming and are between the cylinders. Without them you would get no cooling which is what your description suggests.

[Beach Bum]

We have the inter-cylinder baffles in place.

After you double check the mag timing, your extremely high CHTs are your starting point. The high CHTs are likely the cause of the high oil temp and that is likely the cause of the low oil pressure. Those over 400 degree CHTs are the source. A high CHT would be 100 degrees cooler than your numbers. What did you find on your inter-cylinder baffles? Those are the ones which come from Lycoming and are between the cylinders. Without them you would get no cooling which is what your description suggests.

[Beach Bum]

CHT is a single probe model. After implementing a few attempted fixes at resolving this issue, I'll use a laser on the other cylinders our next test run.

Are both rear cylinders showing about the same temp, and the front ones less?

[Beach Bum]

One mag is new, the other disassembled and inspected. Will double check the mags Mike.

likes been said a couple times in here, but not addressed?, checking INTERNAL mag timing.... not the mag to engine timing... see if they were assembled right..

[sierra bravo]

For reference. See chapter 3 and Lycoming's discussion of CHT. Out of curiosity, what's your EGT temp spread between full rich and peak while in level cruise?

http://www.7ts0.com/manuals/lycoming...LIO-320_OM.pdf

[cgoldy]

I found my cht problem by comparing while running on one mag at a time. It turned out to be a timing issue. The problem ended up being so simple but it took me along time to find it. Now I am usually around the 360 to 380 mark. Dropped 30 degrees!

[garrett490]

We checked the oil screen and it looked normal according to our mechanic. Just some carbon in the screen. Today I flew on one mag at a time in cruise for 3 minutes each. On the left mag the CHT dropped a degree or two to which seemed to go along with the 50 rpm loss, but when switched to the right mag the CHT dropped 20 degrees in about 1 minute with the samee 50 rpm loss. Landed and retimed both mags to engine to ensure that both were set at 25 degrees before TDC. Took the cub back up and did the same test...and the engine still ran cooler on the right mag. Left mag is brand new, right mag has some time on it. Any ideas that explain the difference in CHT temp between the two mags? Lowest CHT temp I got was 382 and that was at 2350 rpm on the right mag. Left was around 402 both was about 403-405.

[Roger Peterson]

Pull the muffler and put in a straight pipe and ck it.

[garrett490]

what will that do?

[Dave Prizio]

Besides external timing magnetos also have internal timing. It would not be surprising to see a mag with some hours on it have the internal timing be off a bit. It is not terribly difficult to adjust the internal timing, but you will need instructions and possibly a special tool to do it, depending on the make and model of magneto you have. A web search should turn up the instructions for your particular mag.

Dave Prizio

[cruiser]

http://www.eaavideo.org/video.aspx?v=972961455001 About 44 min into this he discusses high CHT and claims 2 causes of same, loss of cooling and a lean mixture. If lean mixture CHT will be high ROP and low LOP. You say it does not take much of a pull on the red knob to go lean, is that a hint? Good luck, Jim

[Wingwrench]

Don't confuse internal timing of the mag with setting the E gap.

Internal mag timing is the relationship between the distributor gear and the drive gear and is set on assembly. It won't move unless teeth depart from the gear. It happens but the engine gets quiet. The only way to check it is to take the mag apart and verify the correct timing marks align in accordance with the repair manual.

E gap is set with the points.

[Tim]

What cruiser said, if runs a LITTLE lean it will get hot

[garrett490]

http://www.eaavideo.org/video.aspx?v=972961455001 About 44 min into this he discusses high CHT and claims 2 causes of same, loss of cooling and a lean mixture. If lean mixture CHT will be high ROP and low LOP. You say it does not take much of a pull on the red knob to go lean, is that a hint? Good luck, Jim

I understand. But how do you get more fuel to the cylinders on a carbureted engine when mixture lever on the carb hits the full rich stop? I've read some stuff about drilling out the jet on the vans aircraft forums. And any one know what would cause the CHT to be 20 degrees cooler when running on right mag vs left mag? I have to fly around at 2350 rpm to stay at 395-405 cht then when I need to climb soon as I hit 2500 rpm my temps go up to around 440-450 so I end up lowering nose and pulling back to 2350 rpm and climbing out at 300fpm at 420 degrees. Engine has 15 hours on it as of today. Running Aeroshell 100 Mineral. Oil temps at 220-230.