M20C high CHTs during TO/Climb

[takair]

Back in picture 1 and 2, there appear to be missing screws along top of left baffles and it appears the top plate might be lifting.  There is a good amount of pressure up there and it can open  pretty big leak.  This may not show up when doing flashlight test.

[Matthew P]

On 11/18/2025 at 8:07 PM, Phil123 said:

Mag timing is definitely on the list for the next shop visit. I am not really sure about the Electroair E-Mag. Those definitely advance the timing, but I haven't found any info on when and how they do that.

I didn't think those were available for certified aircraft

[bcg]

My C runs hotter than I'd like as well.  I did several things that cumulatively helped.  First I removed and flushed my oil cooler to clean out any sludge, that made a small difference.  Then I made sure my cowling front was sealed as well as possible and added felt around the accessories where I had big holes on the bottom half, that helped noticeably.  Next I repaired what cracks and holes I could on the dog house and then used aluminum tape to seal everything up as best I could, that made a difference of a few degrees.  I also found that keeping it at 2700 for the entire climb made a big difference, more than anything else individually.  I also climb out at 110 - 120MPH, the climb isn't as fast but the extra airflow keeps me at 400 or less.  One last thing that helps significantly in the hotter months is to top the oil up to 7 quarts, that quart ends up blowing out the breather tube pretty quickly, it does stay in long enough to keep the engine cooler during climb out though, I consider it a sacrifice to the aviation gods.  With all of this, I can keep the hottest cylinder at 400 or less with a shallow climb.  If I try to climb more steeply it'll quickly spike up to 420+ and I nose down a little to increase airflow.

 

I think the biggest things are to make sure the doghouse isn't leaking, keep the airspeed up, prop at 2700 and the sacrificial quart of oil.

[Matthew P]

4 hours ago, bcg said:

My C runs hotter than I'd like as well.  I did several things that cumulatively helped.  First I removed and flushed my oil cooler to clean out any sludge, that made a small difference.  Then I made sure my cowling front was sealed as well as possible and added felt around the accessories where I had big holes on the bottom half, that helped noticeably.  Next I repaired what cracks and holes I could on the dog house and then used aluminum tape to seal everything up as best I could, that made a difference of a few degrees.  I also found that keeping it at 2700 for the entire climb made a big difference, more than anything else individually.  I also climb out at 110 - 120MPH, the climb isn't as fast but the extra airflow keeps me at 400 or less.  One last thing that helps significantly in the hotter months is to top the oil up to 7 quarts, that quart ends up blowing out the breather tube pretty quickly, it does stay in long enough to keep the engine cooler during climb out though, I consider it a sacrifice to the aviation gods.  With all of this, I can keep the hottest cylinder at 400 or less with a shallow climb.  If I try to climb more steeply it'll quickly spike up to 420+ and I nose down a little to increase airflow.

 

I think the biggest things are to make sure the doghouse isn't leaking, keep the airspeed up, prop at 2700 and the sacrificial quart of oil.

What are your magneto timing set at...there is a SB out recommending going from 25 degree timing down to 20 degree timing, lowers CHTs and helps with engine start

[Andy95W]

9 hours ago, Matthew P said:

What are your magneto timing set at...there is a SB out recommending going from 25 degree timing down to 20 degree timing, lowers CHTs and helps with engine start

That does not apply to the M20B/C/D/G, which all have the carbureted O-360.

[Shadrach]

17 hours ago, Matthew P said:

What are your magneto timing set at...there is a SB out recommending going from 25 degree timing down to 20 degree timing, lowers CHTs and helps with engine start

As previously mentioned, the optional 20°  timing is only available for the injected, angle valve engines. 
I am not sure why retarding the timing would help with engine start. If the lag angle is properly set, the mag should fire at 0° degrees  during the start up no matter whether the mag is timed to 20° or 25°.

[bcg]

On 12/28/2025 at 12:17 PM, Matthew P said:

What are your magneto timing set at...there is a SB out recommending going from 25 degree timing down to 20 degree timing, lowers CHTs and helps with engine start

I honestly can't say for sure, David at Dugosh did it for me.  I was there and knew what it was when it was set but, I've slept since then.

[ziggy122]

I was flying daily in AZ for a couple of years, I second the full oil capacity.  I can maintain 7 qts in my C model. In the summer months I would refill to 7-7.5 qts routinely.  That and the airspeed that the others have mentioned. Also, I thought bringing the RPM down made a big difference for me on a hot day climbout, although that may be up for debate.  Your doghouse looks better than mine though--That may be an inspiration for me to do some work!

[Gee Bee Aeroproducts]

There are three baffle seals in ams3320.093 we have from original design.

To replace the original felt , we die cut 

AMS3195-.250 silicone foam 

This is cemented in place with our two part silicone cement.

If you want it correct material let me know.