High Oil Temp?

[MaddMaxx]

I purchased my first Mooney last October, a '74 J-model, and I'm still getting used to how it operates.  This is my first summer with the plane and I've noticed that the oil temperature seems to run high, between the top of the green arc and sometimes tickling the red limit line.  I've noticed this at 7500' MSL, 80deg OAT, mixture ROP, cowl flaps open, ~115 IAS.  I'm not sure if it's truly running hot and something I need to change my flying style for (are these J-model cowls are tighter than most?) or if the oil temp probe is reading incorrectly (It seems to react normally during warm-up and run-up).  Assuming the CHT reads accurate, it stays in the green.

Any thoughts?

[blaine beaven]

J models weren’t produced until 1977… there are some early ones built in 76. So are you sure you have a J?

Generally in my J I do not see high oil temps unless it is a very hot day and I’ve got 5qts or less of oil in the engine due to usage. 
 

What power setting are you running that you’re only getting 115IAS? And is that knots or mph? Indicated isn’t that useful to trouble shoot; true airspeed is a better indicator of performance. At that set up, with full throttle and 2500RPM, I would expect to see at least 145ktas. If I’m not making what I expect to see for TAS then I know there is something wrong. 

[Shadrach]

4 hours ago, blaine beaven said:

J models weren’t produced until 1977… there are some early ones built in 76. So are you sure you have a J?

Generally in my J I do not see high oil temps unless it is a very hot day and I’ve got 5qts or less of oil in the engine due to usage. 
 

What power setting are you running that you’re only getting 115IAS? And is that knots or mph? Indicated isn’t that useful to trouble shoot; true airspeed is a better indicator of performance. At that set up, with full throttle and 2500RPM, I would expect to see at least 145ktas. If I’m not making what I expect to see for TAS then I know there is something wrong. 

In case of oil cooler performance, IAS is more useful that TAS. 

The original post is odd though.  Maybe the “74” was simply a typo. Using the numbers given his TAS is in the mid 130s which is slow to very slow for any M20 airframe depending on whether in mph or KTS. 
There must be more to this story.

[Greg Ellis]

5 hours ago, blaine beaven said:

What power setting are you running that you’re only getting 115IAS? And is that knots or mph? Indicated isn’t that useful to trouble shoot; true airspeed is a better indicator of performance. At that set up, with full throttle and 2500RPM, I would expect to see at least 145ktas. If I’m not making what I expect to see for TAS then I know there is something wrong. 

It does not sound right but I hope for his sake at least it is in Knots because 115 mph would only be about 99 knots!!!  115 knots is at least 132 mph.  Still way off for a J or even an A, B , C, D, E, F, or G....  Heck, that's Cessna 172 speeds!!!

[TNIndy]

One option may be to find a local Mooney pilot with several years of experience and ask them to go up for an hour or so. Together you may see something and short cut lots of troubleshooting on your own. I'm fortunate to have two semi local CFI's with Mooney's and I learn something every time they fly with me. 

[A64Pilot]

I think he’s climbing and has been for awhile, I don’t think this is cruise. 

7,500 MSL and 80F is HOT too, DA would be what? Over 10,000 I’d guess.

I concur on indicated, airplane only knows indicated for stall, cooling etc. It doesn’t know how fast it’s going, it only knows how many air molecules it’s going through in a given time.

If your wanting to see performance sure convert to true, because true is actual if you will.

But still I don’t think I’ve ever seen my oil temp over half way. I’d suspect something blocked, airflow or the cooler itself.

Vernatherm is the easiest thing to check and now that I think about it, it’s the most likely too. The seat could need staking also.

Need to take it to a good mechanic, this isn’t a Mooney “thing” so any good mechanic.

[MaddMaxx]

Thanks everyone for replies.

One correction: It's a '76.

One confirmation: Kias

One more bit of information: 18"@ 2500RPM cruse after a moderate power climb-out from 1400' take-off.

This doesn't sound like a 'Mooney issue', but either a combination of maintenance and a pilot new to the airframe.  I'll see if I can find a local mechanical that has an opening.

 

[Fly Boomer]

On 8/15/2023 at 10:33 PM, MaddMaxx said:

I purchased my first Mooney last October, a '74 J-model, and I'm still getting used to how it operates.  This is my first summer with the plane and I've noticed that the oil temperature seems to run high, between the top of the green arc and sometimes tickling the red limit line.  I've noticed this at 7500' MSL, 80deg OAT, mixture ROP, cowl flaps open, ~115 IAS.  I'm not sure if it's truly running hot and something I need to change my flying style for (are these J-model cowls are tighter than most?) or if the oil temp probe is reading incorrectly (It seems to react normally during warm-up and run-up).  Assuming the CHT reads accurate, it stays in the green.

Any thoughts?

Welcome to MooneySpace.  There are certainly other types where cooling is something you have to watch, but Mooney gets it's performance, in part, from having a smaller frontal area than most other types.  That smaller frontal area translates to tighter cowling and increased focus on temperature control.  There are a ton of J-models around here, so I'm sure you will get a ton of answers.

[201Mooniac]

13 hours ago, MaddMaxx said:

Thanks everyone for replies.

One correction: It's a '76.

One confirmation: Kias

One more bit of information: 18"@ 2500RPM cruse after a moderate power climb-out from 1400' take-off.

This doesn't sound like a 'Mooney issue', but either a combination of maintenance and a pilot new to the airframe.  I'll see if I can find a local mechanical that has an opening.

 

My 1980 M20J doesn't ever have a problem with oil temp, even when CHT gets high in a long hot climb.  I would definitely look for a cause but please make sure your gauge is reading correctly first.  You can test the sender in boiling water to ensure it is reading 212.  I've never flown at 18"/2500 so I can't suggest what my temps would be but if anything, I've found that oil temps in an M20J can be on the low side, never the high side presuming you have enough oil.  This leads me to think you either have a gauge problem, a vernatherm problem, or an oil cooler blockage.

[Sue Bon]

Welcome to MooneySpace Maxx!

My oil temp is hotter during the summer on hot days (30+C). My cruise setting is around 21" and 2400 RPM. During climb it might get to the end of the green arc. If that is happening, I leave the cowl flaps open. As long as the needle is in the green arc, though, it should be ok. If you increase power to over 20", you will fly faster which will help to cool the engine. 115 KIAS is really slow.

 

 

[A64Pilot]

On 8/17/2023 at 11:35 AM, 201Mooniac said:

My 1980 M20J doesn't ever have a problem with oil temp, even when CHT gets high in a long hot climb.  I would definitely look for a cause but please make sure your gauge is reading correctly first.  You can test the sender in boiling water to ensure it is reading 212.  I've never flown at 18"/2500 so I can't suggest what my temps would be but if anything, I've found that oil temps in an M20J can be on the low side, never the high side presuming you have enough oil.  This leads me to think you either have a gauge problem, a vernatherm problem, or an oil cooler blockage.

I’m thinking vernatherm and or the seat needing staking, they do (rarely) go bad and just stop working.

Usually I’ve seen that they would be tested in an oven to heat them up as opposed to hot water, you can’t test the gauge that way unless I guess you have a really long wire  

I’ve only done it with a heat gun on low, you can see them grow when they heat up, they don’t grow much, from memory less than 1/4” but verify that because it’s been a long time. Darn things aren’t cheap, or I’d say just put in a new one, that’s what I did years ago and wasted the money, since then I guess I lost it because I’ve not seen it for years.

This is a pretty good article but I’ve not read the whole thing. I do take exception to putting a glass thermometer down the dip stick, if I did I promise you it would break, just the way my luck runs.

I’ve found an IR thermometer, the ones sort of like a gun where you point and pull the trigger to be invaluable, and you can even use them for barbecuing and uses you haven’t though of until you get one 

https://www.avweb.com/ownership/oil-temperature-control-systems/