High CHT with P-Mag

[GalinHdz]

I just installed dual P-Mags on my Lycoming O-360 A4M and my #3 CHT is running hot. With the older Slick mags I never had a problem. I checked the baffles, they are in good shape and have not changed since the new instal.

CHT 1, 2, and 4 stay just below 400f under my normal cruise but #3 runs around 425f. If I reduce power below 65% then everything drops below 400f but anything above 65% brings the temp on #3 right back up unless I run it very rich, about 12gal/hr.

I am using the "A" curve on the mags and they both are hooked to the same MP point with a "T" connector. I have about 30hrs on the ignition.

Any ideas?

[Kahuna]

Have you checked the ACTUAL timing with a timing light of each ignition?

[Bavafa]

Originally Posted by Kahuna

Have you checked the ACTUAL timing with a timing light of each ignition?

Is the use of timing light in aircrafts, the same as in cars?

If so, I would imagine you will need a long cords to attach to the spark plug wires due to the prop.

[guccidude1]

I have dual P-Mags (jumper wire installed) with an O-360-A4K converted to an -A4M (updraft carb) on my -9A. I also have higher CHTs with the P-Mags vs Slick Mags, especially #3 cylinder. I can keep them all below 400F up to 2500 RPM at altitude burning 8-8.5 gal/hr with 155 KTAS. Baffling is good and oil temps hardly ever see 200F in summer. Dan

[gereed75]

Much has been written here regarding timing and CHT's. Sounds like your timing is advanced from what it was. Search the forums.

Yes you can use an inductive timing light as used on a car engine. Not a big deal, be very careful.

Make sure you are familiar with the timing marks on the flywheel ring and that you have rigged a good timing pointer aligned with engine case split. Know what timing you will be expecting to see. Standard Bendix mags will give a constant advance (20 or 25 degrees) but the electronic ignitions will give a variety of advances dependent on conditions (RPM and MAP). Check with the P-mag people.

[N941WR]

Higher CHTs is very common when swithching from standard mags.

What numbers are you seeing?

Pull your plane in the hangar, turn off all the lights, put a trouble light under the cylinders and look for air leaks. I was able to drop my CHTs by 15 to 20 degrees by simply sealing all my LITTLE air leaks.

[mike newall]

We know all about this........

Fitted dual P Mags with NGK plugs on top and Unison on the bottom.

Had CHT issues from the get go.

Using a US made plenum on standard cowling, ECI IO-360 motor with an MT 3 blade prop.

Always hovering around 400, 430 when stunting.

Anyhow, we swapped the lowers for NGK's this annual and re timed, paying attention to how and where it was timed.

We had damaged a starter casing with kickbacks so suspected an advanced timing.

Spoke with Brad and he suggested re timing on the A curve but set the timing a couple degrees after TDC on #1.

Set it all up at TDC - moved it a puffteenth retarded and set the timing using the blow method on both mags at the same time.

I know - we changed a bunch of stuff at the same time, so we cannot be for sure what cured the issue, but........

We now run at 320, maybe 350 when stunting.

I couldn't believe what a difference it made.

V happy bunnies

[GalinHdz]

Originally Posted by guccidude1

I have dual P-Mags (jumper wire installed) with an O-360-A4K converted to an -A4M (updraft carb) on my -9A. I also have higher CHTs with the P-Mags vs Slick Mags, especially #3 cylinder. I can keep them all below 400F up to 2500 RPM at altitude burning 8-8.5 gal/hr with 155 KTAS. Baffling is good and oil temps hardly ever see 200F in summer. Dan

What numbers do you typically see above 2500 RPM's at altitude?

Originally Posted by N941WR

Pull your plane in the hangar, turn off all the lights, put a trouble light under the cylinders and look for air leaks. I was able to drop my CHTs by 15 to 20 degrees by simply sealing all my LITTLE air leaks.

I already did this and sealed all the tiny little leaks. There were not many I could find. It help a little, but not much.

Originally Posted by mike newall

Spoke with Brad and he suggested re timing on the A curve but set the timing a couple degrees after TDC on #1.

Set it all up at TDC - moved it a puffteenth retarded and set the timing using the blow method on both mags at the same time.

I know - we changed a bunch of stuff at the same time, so we cannot be for sure what cured the issue, but........

We now run at 320, maybe 350 when stunting.

I couldn't believe what a difference it made.

V happy bunnies

Hmmmm, did you do the "puffing" a few degrees before or after TDC on #1? This sounds logical to me. I will try it, see if it helps and report my results.

[glenn654]

Could the more efficient ignition/combustion gained from the EI result in the higher CHTs?

I will be running one PMAG and Slick on my -7.

Glenn Wilkinson

[N941WR]

Originally Posted by glenn654

Could the more efficient ignition/combustion gained from the EI result in the higher CHTs?

I will be running one PMAG and Slick on my -7.

Glenn Wilkinson

We have a winner. Assuming everything else is OK.

The other day I had one of our EICommander customers call and ask about timing, CHT's, etc. He was concerned about his "high" CHTs. When I asked him what "high" was, he replied, "360 degrees". I about fell over, 360 would be great but he wanted 330 or so, which is what he had prior to going to P-mags. I guess it is all relative.

This conversation prompted me to pull out my Lycoming Operator's Manual for O-360's. While we all seem to agree that sub 400 CHTs are ideal, here is what Lycoming states in their manual:

Originally Posted by Lycoming O-360 Operator's Manual

GENERAL RULES
Never exceed the maximum ride line cylinder head temperature limit.

For maximum service life, cylinder head temperatures should be maintained below 435*F (224*C) during high performance cruise operation and below 400*F (205*C) for economy cruise powers.

...

Those temps are a lot higher than any of the conventional wisdom I had heard and my preference is to see CHT's in the 360 to 380*F range.

Your mileage may vary.

PS. I have both of my P-mags set to TDC and am running the A curve. My CHT's run in the range I mentioned above while operating ROP. When LOP, my CHT's will drop into the high 200's.