High oil temps - Metal plate for the back of the oil cooler? 67 M20F

[TheMooneyAnomaly]

Hello!  My CHTs and EGTs seem fine, though oil temp in cruise with cowl flaps open is around 224F and is around 228F with them closed.

I've been looking at discussions on here for what to seek out.

Called Robert Brown of LASAR and he advised that there should be a metal plate on the back side of my cowl-mounted oil cooler with 4 holes in it. He said the purpose is to slow down air flow.

Is anyone familiar with this part? I don't have it on my plane and have not found the piece or drawings/photos online.

 

Thanks!

[McMooney]

is that high?  doesn't seem excessive

[Ragsf15e]

24 minutes ago, TheMooneyAnomaly said:

Hello!  My CHTs and EGTs seem fine, though oil temp in cruise with cowl flaps open is around 224F and is around 228F with them closed.

I've been looking at discussions on here for what to seek out.

Called Robert Brown of LASAR and he advised that there should be a metal plate on the back side of my cowl-mounted oil cooler with 4 holes in it. He said the purpose is to slow down air flow.

Is anyone familiar with this part? I don't have it on my plane and have not found the piece or drawings/photos online.

 

Thanks!

Rumor is that about half have that and half don’t.  Mine doesn’t have it but I have normal 185ish oil temps.  Did you check your vernatherm?  When was the last time the cooler was flushed out?

[N201MKTurbo]

The oil cooler on the early Mooneys is sort of odd. It looks like it would work great where it is located, but it doesn’t. You have to think about how a pressure cowl works. It depends on a pressure differential to get air to flow through the cylinder fins. The early cowls had a huge opening which over supplied the airflow to the upper cowl. With the cowl flaps closed the pressure differential between the upper and lower cowl is relatively small and most of the pressure drop is across the cowl flaps. This makes the pressure in the lower cowl relatively high. This causes a low pressure differential across the oil cooler. There are two kinds of pressure going on here, static pressure and dynamic pressure caused by airflow. There is a lot of air flowing in the lower cowl, it comes down through the cylinders and out the cowl flaps. This airflow goes right by the oil cooler. By putting that plate on the back of the oil cooler, it shields the cooler from the airflow coming down from the cylinders eliminating the dynamic pressure opposing the flow through the oil cooler.

Adding the cowl closure will reduce the airflow into the upper cowl, which puts more of the pressure drop across the cylinders, reducing the lower cowl static and dynamic pressure, which improves flow through the oil cooler.

The ultimate fix is relocating the oil cooler to its modern location above cylinder 4.

[N204TA]

When I first bought my “F,” I was experiencing high oil temps.  The guys at Dugosh fabricated a plate like you described out of a piece of aluminum and bolted it to the back of the oil cooler using standoffs to leave about an inch or so gap between the cooler and the plate.  It made a big difference.

I bought a new cooler when I replaced the engine and opted to try it without the plate.  Seventeen years later, my oil temperature is still comfortably in the green.

[MikeOH]

Is there a drawing or P/N for this 'plate'?  I've tried about everything to get my oil temps out of the 220s with no success; this is a new solution for me!

[takair]

As I recall, there was some service bulletin for C models that added the plate. I think I posted it in another thread some time ago. The intent of the plate was to keep cooler air from cracking the exhaust on #2 cylinder, but I suppose it could help the oil temp. I found that sealing the top and bottom of the cooler helped a little. You will likely find that there are gaps there. 

[takair]

This thread has the discussion and service bulletins. 
 

 

[bcg]

I have the plate on my C, my oil temp is usually 205 - 220, depending on the phase of flight. That's higher than I'd like but, flushing the oil cooler helped bring it down to that from higher. I've also found that adding that 7th quart of oil, even though I know it'll get blown out the breather, helps immensely during climb out, it'll keep me below 200 and keeps my CHTs below 400 without having to make a very shallow climb.

Sent from my Pixel 6a using Tapatalk

[M20F]

On 8/11/2024 at 5:10 PM, takair said:

This thread has the discussion and service bulletins. 
 

 

Except the links are broken, anyone have the SB’s?

[cliffy]

It should also help reduce radiation heating from the exhaust stack

Its simple to make and about the same size as the body of the oil cooler. 

Not really  big deal to install Probably can do it as a Minor Alteration (log book sign off only). 

Do make sure your cowl flaps are opening the correct amount (it varies by model and year)

That makes a big difference in cooling as noted above in that it lets out more air and lowers the "below deck" pressure

Airspeed on my D model doesn't seem to be too affected by cowl flap opening position.  I just leave mine wide open all the time. 

In actuality the air flow coming in the cooler mounted on the lower cowl is not efficient. Most of it slides by the cooler opening

as was demonstrated many years ago by "tufting" the cowl area there. 

I've always wanted to try a small "scoop" just below the cooler opening to see if more air would be passed into the cooler.

[Shadrach]

 

On 8/11/2024 at 10:55 AM, TheMooneyAnomaly said:

Hello!  My CHTs and EGTs seem fine, though oil temp in cruise with cowl flaps open is around 224F and is around 228F with them closed.

I've been looking at discussions on here for what to seek out.

Called Robert Brown of LASAR and he advised that there should be a metal plate on the back side of my cowl-mounted oil cooler with 4 holes in it. He said the purpose is to slow down air flow.

Is anyone familiar with this part? I don't have it on my plane and have not found the piece or drawings/photos online.

 

Thanks!

Are your oil lines fire sleeved? Are they routed under the aluminum heat shield that protects them from the heat of the muffler?  I have no plate on my stock oil cooler and cowl. The only time my oil flirts with 200° is during sustained, summer time climbs. I have to block half of oil cooler off in the cool months to keep temps high enough. If it’s < 20°, I block it completely.

[47U]

11 hours ago, M20F said:

Except the links are broken, anyone have the SB’s?

Try these…

https://www.mooney.com/wp-content/uploads/2020/12/SBM20-93.pdf

https://www.mooney.com/wp-content/uploads/2020/12/SBM20-99.pdf

 

 

[M20F]

File’s uploaded to Mooneyspace for posterity. 

sbm20-93.pdf sbm20-99.pdf

[Skates97]

On 8/11/2024 at 2:06 PM, takair said:

As I recall, there was some service bulletin for C models that added the plate. I think I posted it in another thread some time ago. The intent of the plate was to keep cooler air from cracking the exhaust on #2 cylinder, but I suppose it could help the oil temp. I found that sealing the top and bottom of the cooler helped a little. You will likely find that there are gaps there. 

I made one out of a sheet of aluminum with some standoffs. I think I just used some aluminum tube cut to length for the standoffs. Not sure if it helps with the temps but my goal was protecting the #2 exhaust. There was as you mentioned gaps at the top and bottom between the cooler and the cowl. I cut a couple short strips of the felt that I used around the generator and starter, slipped them in those gaps, then tightened down the bolts. It sealed up quite nicely.

https://www.aircraftspruce.com/catalog/cspages/felt.php?clickkey=5104

On 8/12/2024 at 9:11 AM, bcg said:

I have the plate on my C, my oil temp is usually 205 - 220, depending on the phase of flight. That's higher than I'd like but, flushing the oil cooler helped bring it down to that from higher. I've also found that adding that 7th quart of oil, even though I know it'll get blown out the breather, helps immensely during climb out, it'll keep me below 200 and keeps my CHTs below 400 without having to make a very shallow climb.

Sent from my Pixel 6a using Tapatalk
 

I've kept logs of all my flights since I purchased the plane in 2017 and one thing I track is the oil consumption. I initially subscribed to the "anything over 6 qts gets blown out" theory so I would add a quart when I got to 5 to bring it back up to 6. Then I got thinking that I put in 7 quarts at an oil change and it doesn't quickly drop to 6 qts. I decided to start adding a qt when I got to 6 bringing it back up to 7 instead of waiting for it to get down to 5. The end result of tracking it was that it took the same number of hours to drop from 7 down to 6 as to drop from 6 down to 5. Since then I have stuck with adding a qt when I get down to 6.

Here's a pic of the plate, you can see the felt at the top as well.

[bcg]

I've kept logs of all my flights since I purchased the plane in 2017 and one thing I track is the oil consumption. I initially subscribed to the "anything over 6 qts gets blown out" theory so I would add a quart when I got to 5 to bring it back up to 6. Then I got thinking that I put in 7 quarts at an oil change and it doesn't quickly drop to 6 qts. I decided to start adding a qt when I got to 6 bringing it back up to 7 instead of waiting for it to get down to 5. The end result of tracking it was that it took the same number of hours to drop from 7 down to 6 as to drop from 6 down to 5. Since then I have stuck with adding a qt when I get down to 6.
Here's a pic of the plate, you can see the felt at the top as well.

I also track mine, I lose that 7th quart in an hour, the 6th will take 5 hours to disappear. I'm willing to sacrifice that 7th quart to the aviation gods to keep my temps down though, seems a small trade off. Oil is a lot cheaper than cylinders.

Sent from my Pixel 6a using Tapatalk

[Skates97]

6 hours ago, bcg said:

I also track mine, I lose that 7th quart in an hour, the 6th will take 5 hours to disappear. I'm willing to sacrifice that 7th quart to the aviation gods to keep my temps down though, seems a small trade off. Oil is a lot cheaper than cylinders.

Sent from my Pixel 6a using Tapatalk
 

Interesting, with a fresh oil change on the old engine I would get right to 10 hours before it was down to 6. The further into the oil change it would get down to about 6-8 hours to go from 7 to 6. Not enough time on the new engine to know yet, but I agree with you on the trade off for the price of oil. I'm willing to sacrifice a quart too!

[TheMooneyAnomaly]

On 8/11/2024 at 11:21 AM, Ragsf15e said:

Rumor is that about half have that and half don’t.  Mine doesn’t have it but I have normal 185ish oil temps.  Did you check your vernatherm?  When was the last time the cooler was flushed out?

Since this post, my A&P has flushed the cooler - found no concern or debris.  He also tested the function of the vernatherm and that looked good.

The oil lines are from 2021 and seem to be in good order.

 

He did find one thing - I have the oil filter relocation STC.  This leads to a connector being mounted to the back of the engine where multiple oil outflows exist. The incorrect gasket was present, blocking about 40% of the larger oil flow hole (pardon my lack of vocabulary on this).  We are waiting for the replacement gasket to arrive.

[TheMooneyAnomaly]

On 8/11/2024 at 10:59 AM, McMooney said:

is that high?  doesn't seem excessive

That's something I have been curious about.  I'd say it is.  Yellow arc aside, my aircraft ranges in the top 91% to 98% of the 200hp cohort on Savvy with regards to high oil temp.  I may have worded that wrong - it is at the hottest range of the cohort.

[TheMooneyAnomaly]

On 8/13/2024 at 11:54 PM, Shadrach said:

 

Are your oil lines fire sleeved? Are they routed under the aluminum heat shield that protects them from the heat of the muffler?  I have no plate on my stock oil cooler and cowl. The only time my oil flirts with 200° is during sustained, summer time climbs. I have to block half of oil cooler off in the cool months to keep temps high enough. If it’s < 20°, I block it completely.

The oil lines are fire sleeved and fresh from 2021.  They are routed below the metal plate mounted near the bottom of the cowl area.