Mooney M20E 1975 CHT high but oil temp low

[ighazali]

On 10/25/2025 at 9:24 PM, 47U said:

I think you can make the new baffles following the pattern of the baffles that you remove.  It looks like the rear baffle is the worst offender, the sides and front might be ok.

Other notes (please forgive)… there’s a plenum just outboard of the upper left engine mount.  I think there’s supposed to be a scat duct attached that directs cooling air down to the fuel pump on the back of the accessory case.  Also, there’s a baffle screw missing on the rear baffle joint to the side baffle, third hole down… or is that where the ignition lead adel clamp is supposed to go(?).  Regardless, that adel clamp is not secure and with the screw loose, possibly another source of air leakage.  Lastly the prop governor cable is chaffing on the engine mount tube.  There’s some spiral wrap on it, but it looks like the paint is gone and some rust forming on the tube.  

 

Thank you so much all of this is great information! I will get that engine mount tube painted. Also I will have a screw install on the right side and the bottom screw tightened, I will also get with my A&P and re do the back of the baffles and get that scat tubing in to get it corrected. I will also see what I can do with that prop governor cable!

[ighazali]

I ran the engine 25 degrees lean of peak today and granted today was a slightly cooler day but check the temps. I am sure once I get the things corrected you all listed it will definitely go down!

[Slick Nick]

9 hours ago, ighazali said:

Airplane had come out of a fresh annual and I was able to get 10,000 dropped for inop pitot heat and possibly "faulty cht guage" is what the A&P IA said. 

At least that leaves you some money to get this stuff fixed. 

So, you're sure the CHT gauge is working properly? 

[ighazali]

16 hours ago, Slick Nick said:

At least that leaves you some money to get this stuff fixed. 

So, you're sure the CHT gauge is working properly? 

Based on the indications I am receiving yes. When I run it lean of peak I see CHT temps cooler, when I run it rich of peak I see it hotter just like my initial picture shows. My only thing is that is it normal to see oil temps as cool as shown?

[Slick Nick]

7 hours ago, ighazali said:

Based on the indications I am receiving yes. When I run it lean of peak I see CHT temps cooler, when I run it rich of peak I see it hotter just like my initial picture shows. My only thing is that is it normal to see oil temps as cool as shown?

I was referring to your last post where your A&P diagnosed a “faulty CHT gauge”. 

[ighazali]

On 10/28/2025 at 7:44 AM, Slick Nick said:

I was referring to your last post where your A&P diagnosed a “faulty CHT gauge”. 

That is what we thought based on temps but after diagnosing the sensor and moving it to cylinder 1 and ran it for a flight and back to cylinder 3 we came to the conclusion that it was working properly as cylinder 1 temps were super cool since it is in front of the engine bay!

[Slick Nick]

The sensor is usually located on #3 because it’s the hottest cylinder. 

So, you’ve flown it a few times since trying to diagnose this issue, have you fixed the baffles yet?

[ighazali]

On 10/29/2025 at 4:36 PM, Slick Nick said:

The sensor is usually located on #3 because it’s the hottest cylinder. 

So, you’ve flown it a few times since trying to diagnose this issue, have you fixed the baffles yet?

Yes I have and temps have been dropping and are not as high as they used to be!

[Gee Bee Aeroproducts]

We have dies to cut silicone with fiberglass.093

ans3320

some models have felt

we die cut ams3195-.250 silicone foam

 

we have all the lycoming dies

.032 on most engine gaskets 

 

are capacity is 4K seals per hour as we have two atom clicker presses 

 

[ighazali]

So I am still having high CHT on climb out according to the original gauges but my oil temperature is well within green range.

So far I have replaced the baffle seals in the back with new baffle seals from a Mooney service center and they re did the scat duct down to the fuel pump where it goes.

I am still not convinced that it is the gauges themselves as when the engine is cool the gauges are reporting cool and as it warms up CHT start heading in the green shortly followed by after the oil temperature.

I am using 15w-50 for the oil type by Aeroshell.

I have attached images of how the baffling looks and everything seals properly even when a light is shined. During the descent the CHT do show very cool temperatures and in cruise they back down a bit after leaving cowl flaps open and then closing them when CHT temperatures are within the green range. Only in the climb out at an airspeed of 120MPH well above VY do I see these high temperatures where I am kissing redline with MP 26" and RPM 2500. 

 

Now I did notice that when I start running her a bit lean of peak in the climb out my CHT stay relatively cool compared to running it ROP. 

[skykrawler]

The rear seal just looks too high.  If there is an 1" clearance between the baffle metal and the top cowl then the seal should extend maybe 2...2.5" above the metal baffle and curve nicely and firmly against the top cowl.

Good engine management is much easier with multi probe engine monitor.

Presumably the fuel flow at full power is correct - 19+gph.    Fuel flow is important for cooling at full power.  If that was a factory overhaul it should have been close right from the factory.

 

[takair]

Disappointing the seals did not help, but I think they can still be improved.  In the image, I circled three spots in the back that look like they would leak.  I circled two spots in the front to check.  I can’t see, but be sure the front cowl seals are sealing too.  This is often ignored, also around the starter and alternator.

You mentioned climbing lean of peak and lower CHTs?  Were you less than 75% power (65% better)?  Have you tried full power, full rich climb?  What fuel flows?  You could be running very lean in the climb due to fuel servo issue.  At climbed power, you should normally be about 200 ROP +-.  Hard to check because you don’t want to lean too much at those settings, but you get a sense of it when you level off by how much you have to lean to get to peak…..do you know that value?

[MikeOH]

Question for the experts: What is the desired/acceptable plenum pressure (say, in inches of water)?  Seems like it would be pretty easy to rig a water manometer and monitor the actual pressure even in flight.  That would be a pretty good indicator as to whether the baffling is acceptable, I'd think.

[takair]

1 hour ago, MikeOH said:

Question for the experts: What is the desired/acceptable plenum pressure (say, in inches of water)?  Seems like it would be pretty easy to rig a water manometer and monitor the actual pressure even in flight.  That would be a pretty good indicator as to whether the baffling is acceptable, I'd think.

I cheated since I couldn’t recall the exact value, but 6-7” seems popular, which is quite low pressure differential. Thus the criticality of sealing the leaks. The engine cylinders are quite a large leak to begin with. There are likely some variations depending on where you measure, due to ram effect, but the key question is, does the air go through the cylinders or out a hole. The cylinders require a bunch of turns, so the smart air takes the easy way out. 

[Gee Bee Aeroproducts]

Bad seals 

design

thickness

one inch gap in loss equals 40 degrees on cht

we die cut to original design and .093 thickness with fiberglass reinforcement.

[Gee Bee Aeroproducts]

15 hours ago, ighazali said:

So I am still having high CHT on climb out according to the original gauges but my oil temperature is well within green range.

So far I have replaced the baffle seals in the back with new baffle seals from a Mooney service center and they re did the scat duct down to the fuel pump where it goes.

I am still not convinced that it is the gauges themselves as when the engine is cool the gauges are reporting cool and as it warms up CHT start heading in the green shortly followed by after the oil temperature.

I am using 15w-50 for the oil type by Aeroshell.

I have attached images of how the baffling looks and everything seals properly even when a light is shined. During the descent the CHT do show very cool temperatures and in cruise they back down a bit after leaving cowl flaps open and then closing them when CHT temperatures are within the green range. Only in the climb out at an airspeed of 120MPH well above VY do I see these high temperatures where I am kissing redline with MP 26" and RPM 2500. 

 

Now I did notice that when I start running her a bit lean of peak in the climb out my CHT stay relatively cool compared to running it ROP. 

Should be double wall sceet not scat

Non finished ends , that's poor parts support for a Mooney shop .

 

[EricJ]

3 hours ago, MikeOH said:

Question for the experts: What is the desired/acceptable plenum pressure (say, in inches of water)?  Seems like it would be pretty easy to rig a water manometer and monitor the actual pressure even in flight.  That would be a pretty good indicator as to whether the baffling is acceptable, I'd think.

Absolute pressure likely isn't important, but pressure difference from top to bottom (i.e., above and below cylinders) matters.   People check the delta with pressure sensors, but I don't know what typical numbers are.  

[ighazali]

8 hours ago, takair said:

Disappointing the seals did not help, but I think they can still be improved.  In the image, I circled three spots in the back that look like they would leak.  I circled two spots in the front to check.  I can’t see, but be sure the front cowl seals are sealing too.  This is often ignored, also around the starter and alternator.

You mentioned climbing lean of peak and lower CHTs?  Were you less than 75% power (65% better)?  Have you tried full power, full rich climb?  What fuel flows?  You could be running very lean in the climb due to fuel servo issue.  At climbed power, you should normally be about 200 ROP +-.  Hard to check because you don’t want to lean too much at those settings, but you get a sense of it when you level off by how much you have to lean to get to peak…..do you know that value?

I lean it at 3000' when I start bringing the power back and open the ram air induction to about 25 degrees lean of peak. I usually lean it during the climb to lean of peak until I see a slight reduction in engine performance and then leave it at that and I have seen similar CHT temps to what most M20E/F owners are getting. 

I have ran it rich of peak but still the same on the CHT which is high. I have marked my EGT gauge which is usually my typical cruise between 4500-7500'  is roughly 250-275 degrees is peak for me.

I do not have a fuel flow gauge at all just a fuel pressure gauge.

I have attached a picture for you to see where my peak is marked. I have also attached a few images of engine temperatures when operating rich and not touching the mixture at all. And a better image of the front nose area.

I am starting to now suspect that it may be the CHT sensor. Is that a likely possibility? 

I recently did a 12 hour trip in the Mooney from MOD-PHX-LAS-MOD and airplane operated just fine but CHT were showing at the edge of the green especially the afternoon climb out of Vegas and Phoenix as it was a bit warm. 

My oil temperature stays relatively cool despite CHT's being that high. 

[takair]

For some reason I thought you had multi cylinder CHT.  Having only 1, I suppose it could read false high.  Yes, that should be checked.  I find your leaning in climb unusual.  Maybe I’m old school, but I typically start the climb full rich and full power.  I note my EGT and hold that through the climb.  In other words, I only lean enough to maintain that.  Leaning more aggressively at high power risks detonation and hot CHTs.  Aggressive lean of peak in climb can reduce ChT but with reduced power, extending your climb.  Maybe try a full rich, full power climb and see what happens….of course if the temp goes up…don’t continue.  Can’t recall, was magneto timing checked?  As a side note, absolute values of EgT vary too much cylinder to cylinder and aircraft to aircraft to be very useful.  

[MikeOH]

10 hours ago, ighazali said:

I usually lean it during the climb to lean of peak until I see a slight reduction in engine performance and then leave it at that

Hmm, sorry but I wouldn't recommend that.  I lean to maintain full power sea level EGTs (mid 1200s for my plane) until I'm at cruise; only then do I go LOP.

[ighazali]

21 hours ago, takair said:

For some reason I thought you had multi cylinder CHT.  Having only 1, I suppose it could read false high.  Yes, that should be checked.  I find your leaning in climb unusual.  Maybe I’m old school, but I typically start the climb full rich and full power.  I note my EGT and hold that through the climb.  In other words, I only lean enough to maintain that.  Leaning more aggressively at high power risks detonation and hot CHTs.  Aggressive lean of peak in climb can reduce ChT but with reduced power, extending your climb.  Maybe try a full rich, full power climb and see what happens….of course if the temp goes up…don’t continue.  Can’t recall, was magneto timing checked?  As a side note, absolute values of EgT vary too much cylinder to cylinder and aircraft to aircraft to be very useful.  

I will try keeping it rich all the way until cruise on my next flight this Thursday. Now is there any point you would continue leaning it for example around 3000 or do you not touch it until you get to your cruise altitude for example 6-7000 feet? Magneto timings I have not checked yet but I may be able to get that done this Thursday. I will also see if the shop can adjust those baffle seals as well for a better seal, and possibly even check the CHT sensor! 

I may just bite the bullet and go for JPI EDM 830 just still finding a shop that has the time to get it done. Any recommendations on any other engine monitor or is that a good choice?

[ighazali]

One of my magnetos is an electronic ignition system not sure if that makes a difference. But it is the surefly one I believe!

[takair]

16 minutes ago, ighazali said:

I will try keeping it rich all the way until cruise on my next flight this Thursday. Now is there any point you would continue leaning it for example around 3000 or do you not touch it until you get to your cruise altitude for example 6-7000 feet? Magneto timings I have not checked yet but I may be able to get that done this Thursday. I will also see if the shop can adjust those baffle seals as well for a better seal, and possibly even check the CHT sensor! 

I may just bite the bullet and go for JPI EDM 830 just still finding a shop that has the time to get it done. Any recommendations on any other engine monitor or is that a good choice?

You might try staying rich just to see what the temps do. Most folks lean to maintain EGT as they climb. For example, if my climb EGT starts at 1200, I will gradually lean to maintain that (I cheat since I have an Auto-Lean system that does it for me). The idea is that you maintain a rather rich mixture to stay away from detonation when at high power and poor cooling. Magneto timing can be a problem if advanced too far. Surefly is the same, be sure the timing is proper. At high power, the Surefly should not be advancing. Since your cruise temps. sound to be reasonable, I’m not so sure you will find an issue with timing. As far as engine analyzers, I may not be the right person since I myself have an antique, but others will chime in or you will find a number of threads on the topic. 

[FlyingDude]

1 hour ago, ighazali said:

One of my magnetos is an electronic ignition system not sure if that makes a difference. But it is the surefly one I believe!

If it's plumbed to the MAP, then it will increase the advance, which will lead to higher cht. I gained about 10F on CHT after installing surefly. But it's still way below high range.

You might be leaving the mixture just above peak, which maximizes CHT. 

[Gee Bee Aeroproducts]

On 1/19/2026 at 2:20 AM, ighazali said:

So I am still having high CHT on climb out according to the original gauges but my oil temperature is well within green range.

So far I have replaced the baffle seals in the back with new baffle seals from a Mooney service center and they re did the scat duct down to the fuel pump where it goes.

I am still not convinced that it is the gauges themselves as when the engine is cool the gauges are reporting cool and as it warms up CHT start heading in the green shortly followed by after the oil temperature.

I am using 15w-50 for the oil type by Aeroshell.

I have attached images of how the baffling looks and everything seals properly even when a light is shined. During the descent the CHT do show very cool temperatures and in cruise they back down a bit after leaving cowl flaps open and then closing them when CHT temperatures are within the green range. Only in the climb out at an airspeed of 120MPH well above VY do I see these high temperatures where I am kissing redline with MP 26" and RPM 2500. 

 

Now I did notice that when I start running her a bit lean of peak in the climb out my CHT stay relatively cool compared to running it ROP. 

Should be double wall sceet not scat

Non finished ends , that's poor parts support for a Mooney shop .