Mooney M20E 1975 CHT high but oil temp low

[ighazali]

Have not had any issue but have a concern with the cht being high. When in cruise flight they cool down and in a cruise climb at 120mph they are running at the edge of the green arch. Also in ground operation with cowl flaps open CHT rises pretty rapidly not to exceed the red line. Attached is a picture of the engine temps and instrumentation, picture was taken during a steep turn maneuver, but have been seeing the same indications up until reaching cruise flight and then closing cowl flaps after seeing cht decreasing. Not sure if it may be faulty due to oil temp running cool. Engine only has 50 hours SMOH. 

[47U]

9 hours ago, ighazali said:

When in cruise flight they cool down and in a cruise climb at 120mph they are running at the edge of the green arch. Also in ground operation with cowl flaps open CHT rises pretty rapidly not to exceed the red line.

Welcome… pretty E model you’ve got there.

I’m a C owner, O-360, but my CHT doesn’t act that differently than yours.  Of course, I have a doghouse, which presumably your ‘75 E doesn’t have.  And you have an ARI or SWTA cowling mod?  I’m not sure what affect that has on CHTs.  At only 50 hrs SMOH you could still be breaking in the cylinders, especially if the overhaul shop didn’t run it on the test cell.  Was the overall done with chrome  cylinders?  They might have a reputation for running hotter CHTs.  

So, start with standard troubleshooting the baffling.  Good sealing against the cowling, the flexible pieces are bent the correct direction, gaps around the starter and alternator, inter-cylinder baffles on bottom of the cylinders are installed correctly.  There’s many threads on lowering CHTs.

As far as low oil temperature, I’d start with verifying the gauge is accurate.  The sender can be put in boiling water to verify.  It that’s good, then looking at the vernatherm to make sure it’s opening and closing properly.  There’s threads on that, too.   

An engine monitor is a good thing… my factory CHT runs hotter on the scale than what is indicated on my UBG-16.

Top picture is from the sales ad showing the gauge scales more clearly…

[Shadrach]

Very good advice above.  I fly an F which should have the same engine and cowling combo as your E, save for the cowl enclosure which I do not have. The only thing I can add to the comment above is that if indeed your CHTs are running in the mid to high 400s in cruise, that is much hotter than any angle valve Lycoming I've ever operated. In my experience, angle valve IO360s usually run considerably cooler than parallel valve O-360s.  My IO360 runs low 300s in the Midatlantic summertime temps. In winter, #1 and #4 ure usually in the high 200s. Excursions to 400 are rare and would require hot OATs, low IAS, high deck angle and high power.  It would require an extended period of inattention for any of my CHTs to exceed 375.

Verify the instrument's accuracy before you anything.

[takair]

CHT seems high for your model. I’m curious where your oil cooler is?  The flow pattern with cylinders vs oil are different depending on configuration. As other sugggested, you might not be broken in. What is your oil burn rate?  Any pictures of the engine installation you can share?

[47U]

3 hours ago, takair said:

I’m curious where your oil cooler is?

Screenshot from aircraft.com… oil cooler is on the front cowl, not relocated behind #4 cylinder.  There weren’t any pics in the ad with the cowling removed.

[ighazali]

On 10/7/2025 at 8:57 AM, 47U said:

Welcome… pretty E model you’ve got there.

I’m a C owner, O-360, but my CHT doesn’t act that differently than yours.  Of course, I have a doghouse, which presumably your ‘75 E doesn’t have.  And you have an ARI or SWTA cowling mod?  I’m not sure what affect that has on CHTs.  At only 50 hrs SMOH you could still be breaking in the cylinders, especially if the overhaul shop didn’t run it on the test cell.  Was the overall done with chrome  cylinders?  They might have a reputation for running hotter CHTs.  

So, start with standard troubleshooting the baffling.  Good sealing against the cowling, the flexible pieces are bent the correct direction, gaps around the starter and alternator, inter-cylinder baffles on bottom of the cylinders are installed correctly.  There’s many threads on lowering CHTs.

As far as low oil temperature, I’d start with verifying the gauge is accurate.  The sender can be put in boiling water to verify.  It that’s good, then looking at the vernatherm to make sure it’s opening and closing properly.  There’s threads on that, too.   

An engine monitor is a good thing… my factory CHT runs hotter on the scale than what is indicated on my UBG-16.

Top picture is from the sales ad showing the gauge scales more clearly…

Thank you! I believe it is the ARI cowling mod not too sure but I have attached a picture. The oil temperature gauge seems to be working properly, when first started shows cold and then slowly climbs into the green arc but hardly ever gets warmer then the image you have cropped. The CHT are high initially but once cruised out and cowl flaps closed it starts to cool off and definitely cools off with cowl flaps open in the descent. I am still getting used to all the Mooney quirks but I love it so far! Thank you so much for your detailed response!

[ighazali]

On 10/8/2025 at 5:28 PM, takair said:

CHT seems high for your model. I’m curious where your oil cooler is?  The flow pattern with cylinders vs oil are different depending on configuration. As other sugggested, you might not be broken in. What is your oil burn rate?  Any pictures of the engine installation you can share?

Current oil burn rate is about 6.35 hours a quart. Everytime it is below 6 I add a qt however I do notice that the oil just spits out of the breather tube so had some advice to wait until it is at 5qt to add one. I just reached 60 hours on the engine going to go for an oil change this weekend and get the oil changed from w100 to 15w-50. Suppose to run better in California due to the cold and hot weather. I will also do an oil analysis. The log book says the engine had gotten replaced in 2023 and the previous owner had only put 44 hours on that engine since his time from Dec. 2023- July 2025. Aircraft was not flown as regularly as I am flying. 

[ighazali]

On 10/8/2025 at 8:54 PM, 47U said:

Screenshot from aircraft.com… oil cooler is on the front cowl, not relocated behind #4 cylinder.  There weren’t any pics in the ad with the cowling removed.

I have a video of when I did the pre buy with the cowling removed. I have posted screenshots from it below. May not be the best pictures but this is what I have so far!

[takair]

I would be suspicious of your baffle seals.  They look too wrinkly. By the witness marks they do not look like they are sealing. I suspect they would fail the light test, where you backlight them and look for light comeing through. Would consider trimming them for a better fit. 

[ighazali]

Here are a couple pictures from today. One in the morning and one at night!

[Slick Nick]

Those baffle seals look janky as hell. I’d start there for sure. 

[ighazali]

1 hour ago, Slick Nick said:

Those baffle seals look janky as hell. I’d start there for sure. 

How do I go about fixing them I am new to all of this!

[ighazali]

Can someone also send a link on which baffle seals to buy to get it redone please?

[takair]

It’s hard to describe how to fix them except to suggest looking at pictures of others here on the forum.  It could be as simple as slotting them so they sit flush with the cowl.  They may actually be too wide as well.  Not sure you need new seals, so much as they need adjustment.  As for where to buy, there are various levels.  Aircraft Spruce has raw materials.  @Gee Bee Aeroproducts often shows pictures of the very nice seals he sells.  McFarlane also has a unique seal they sell.  This may not be a 100% solution, but certainly a starting point.

[cbarry]

Is it possible the mag timing is off?  I’m not a mechanic, but this may be an item to have checked that can affect CHTs. As others have mentioned, the baffling’s appearance is suspect.  Another thing to note is fully closed  cowl flaps may be causing a little too much back pressure on the airflow entering the cowling.  

[Gee Bee Aeroproducts]

We die cut two original pattern from a 50" wide sheet

using a atom 25ton clicker press

 

same as valve cover gasket's 

Ams3320.093

your loosing 45/65 degrees on cooling with all those gaps

 

You can buy a sheet and do yourself if you have the correct pattern.

M20m Bravo shown also 

[Fly Boomer]

8 hours ago, ighazali said:

How do I go about fixing them I am new to all of this!

I don’t mean to be flip, but you need to find a mechanic who knows something about airplanes.  Doesn’t have to be a Mooney mechanic.  Any moderately competent aircraft mechanic can do much better than what you have now.

[ighazali]

11 hours ago, Fly Boomer said:

I don’t mean to be flip, but you need to find a mechanic who knows something about airplanes.  Doesn’t have to be a Mooney mechanic.  Any moderately competent aircraft mechanic can do much better than what you have now.

Just took the airplane in for an oil change removed the cowling and here are better pictures of the baffling. Measured the baffling and it is about 3" so going to order it from spruce and get it repaired ASAP with the pitot heat.

[ighazali]

14 hours ago, cbarry said:

Is it possible the mag timing is off?  I’m not a mechanic, but this may be an item to have checked that can affect CHTs. As others have mentioned, the baffling’s appearance is suspect.  Another thing to note is fully closed  cowl flaps may be causing a little too much back pressure on the airflow entering the cowling.  

Checked Mag timings today and they are normal! 

[ighazali]

12 hours ago, Gee Bee Aeroproducts said:

We die cut two original pattern from a 50" wide sheet

using a atom 25ton clicker press

 

same as valve cover gasket's 

Ams3320.093

your loosing 45/65 degrees on cooling with all those gaps

 

You can buy a sheet and do yourself if you have the correct pattern.

M20m Bravo shown also 

Where can I find the pattern for the M20E variant? I see a ton of info on the J models but hardly any on the M20. Thank you!

[47U]

On 10/24/2025 at 1:57 AM, ighazali said:

I have a video of when I did the pre buy with the cowling removed. I have posted screenshots from it below.

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.  

 

[skykrawler]

Whoever did the engine install is responsible for those baffle seals unless somebody messed with it afterwards.

That's awful.

Also, when reinstalling the cowl the seals must be checked or proper positioning - every time.

The (metal) baffles also wrap around the bottom of the cylinder and are held tight to the fins with springs.  Check that those are intact and doing their job.

[Slick Nick]

The side baffle seals might be okay, but that aft one is horrible. You can see where a large section of it is folded backwards, and there’s a giant hole where there should be a duct attached. If you’re not using ducting there, plug it off. I bet by fixing those two things alone, you’ll drop your CHT’s by 50*. 

Didn’t you recently purchase this airplane? How did any of this make it past the pre buy inspection? 

[Fly Boomer]

52 minutes ago, Slick Nick said:

Didn’t you recently purchase this airplane? How did any of this make it past the pre buy inspection? 

Or annual.

[ighazali]

7 hours ago, Slick Nick said:

The side baffle seals might be okay, but that aft one is horrible. You can see where a large section of it is folded backwards, and there’s a giant hole where there should be a duct attached. If you’re not using ducting there, plug it off. I bet by fixing those two things alone, you’ll drop your CHT’s by 50*. 

Didn’t you recently purchase this airplane? How did any of this make it past the pre buy inspection? 

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.