low oil temp in 252

[Wallywingtip]

We have consistently low oil temp in cruise of about 145 degrees F. Too low to burn off moisture, so we are concerned. Pressure is normal.

We have changed out the vernatherm, and lowered the cover plate on top of the oil cooler, and have seen no change. Engine baffles seem good. 

Any suggestions are appreciated. We're scratching our heads.

brentvogan@gmail.com 

 

[M20F]

Have you checked that the probe is reading correctly?

[Wallywingtip]

3 minutes ago, M20F said:

Have you checked that the probe is reading correctly?

No. but both the EDM and the primary are reading low, so we thought it real.

[redbaron1982]

I had the same issue on my J. The CFI that's helping me with the transition training put  aluminum tape to cover 1/3 of the oil cooler and now oil temperature is around 160/170.

[carusoam]

41 minutes ago, Wallywingtip said:

No. but both the EDM and the primary are reading low, so we thought it real.

Welcome aboard Wally!

Hmmmm…

1) do you have one probe feeding two indicators?

2) OilT thermistors typically fail low, slowly over time…

3) test the probe in boiling water…

4) use an IR thermometer to compare to the OilT gauge…

5) OilT in the green arc is acceptable… is it below the green?

6) The vernatherm controls the OilT… if it has opened to a low flow to the cooler… then stays too low…. Oil cooler block(ask your mechanic)

7) Vernatherm can be tested in heated water as well… heat until it activates, compare to what it is supposed to do…

8) some People in the north use an oil cooler block for super cold days…

What is the OAT where you are flying?  -40?

9) what is the oil cooler cover plate that you are describing? An oil cooler block?

Sounds like the oil cooler isn’t being blocked off enough/properly…

Do you know @M20Doc?

Pp thoughts only, not a mechanic…

Best regards,

-a-

[Wallywingtip]

30 minutes ago, carusoam said:

Welcome aboard Wally!

Hmmmm…

1) do you have one probe feeding two indicators?

2) OilT thermistors typically fail low, slowly over time…

3) test the probe in boiling water…

4) use an IR thermometer to compare to the OilT gauge…

5) OilT in the green arc is acceptable… is it below the green?

6) The vernatherm controls the OilT… if it has opened to a low flow to the cooler… then stays too low…. Oil cooler block(ask your mechanic)

7) Vernatherm can be tested in heated water as well… heat until it activates, compare to what it is supposed to do…

8) some People in the north use an oil cooler block for super cold days…

What is the OAT where you are flying?  -40?

9) what is the oil cooler cover plate that you are describing? An oil cooler block?

Sounds like the oil cooler isn’t being blocked off enough/properly…

Do you know @M20Doc?

Pp thoughts only, not a mechanic…

Best regards,

-a-

Thank you for all these good ideas. 

The low temp happens in summer and winter - approx. the same readings.

Not below the green but Savvy says too low to burn off moisture in the oil, and well below the cohort. 

We'll check the other items you list. Thank you.

[A64Pilot]

Lycoming’s take on oil temp, bottom line is oil at its hottest point is significantly hotter than indicated, if moisture is building up it will turn the oil milky.

Yes I know you don’t have a Lycoming, but I don’t have a Conti slide

‘You may not have a problem, especially if your OCI is 25 hours

In order to detect lower levels of moisture, either the crackle test or have it analyzed for moisture, I’ve never had it analyzed. I believe if it’s not turning milky at all, the level of moisture isn’t a concern.

My J also runs low as in bottom of the green temp

[redbaron1982]

Regarding if the sensor is working, I understand that the failure mode of temperature sensors affects the whole range, so I think if you have an EIS where you can see precisely the oil temperature and when the airplane is completely cool it reads something close to room temperature, then I think you can rule out the sensor.

[Wallywingtip]

8 minutes ago, A64Pilot said:

Lycoming’s take on oil temp, bottom line is oil at its hottest point is significantly hotter than indicated, if moisture is building up it will turn the oil milky.

In order to detect lower levels of moisture, either the crackle test or have it analyzed for moisture, I’ve never had it analyzed. I believe if it’s not turning milky at all, the level of moisture isn’t a concern.

My J also runs low as in bottom of the green temp

That is good to know, though we have a continental. Oil colour is normal.

[Wallywingtip]

2 minutes ago, redbaron1982 said:

Regarding if the sensor is working, I understand that the failure mode of temperature sensors affects the whole range, so I think if you have an EIS where you can see precisely the oil temperature and when the airplane is completely cool it reads something close to room temperature, then I think you can rule out the sensor.

great idea. Thanks.

[carusoam]

Keep in mind… Room temperature/hangar temperature/OAT in Canada… depending on where the plane is parked.

the CHTs, OAT, OilTs should all be reading similarly after being unused for a day…

oil hits the highest temp in the exhaust valve guides… small volume, short duration… but, our guidance from the POH is to use the ship’s oil gauge using the ship’s OilT probe in the standard location… 

Best regards,

-a-

[A64Pilot]

36 minutes ago, Wallywingtip said:

That is good to know, though we have a continental. Oil colour is normal.

Understood, but any turbo adds a significant amount of temp to the oil. Before I started modifying the aircraft I’d first ensure I had a problem.

Yes I know up in the Great White North it’s been common practice forever to block off cooler airflow to get oil temps up to normal.

I live in Florida, and my J oil temp runs the bottom of the green in Florida temps, in a hard climb with cyl head temps higher than I like the oil temp still isn’t halfway.

I know you don’t have a J, but would think if I were up there with you my oil temp would be low too.

What we need of course is an oil cooler cowl flap, I would have expected an STC’d one by now, but I guess people are happy with tape and block off plates.

Usually as a general statement the factory oil temp sender is located after the oil cooler and any aftermarket indicator uses it’s own sensor often located in the oil galley on the block, but still after the cooler and before the turbo and often the aftermarket temp will run higher than factory, but it should show a different temp, if not I’d be suspicious. The testing is as simple as putting the tip of the sensor in boiling water.

I had one customer that spent thousands of dollars on an oil temp problem on his turbine, and I went out to help and found it was just a sensor error. I knew when I turned on the battery on a cold engine and his oil temp was 60C or something similar. If both of your instruments use one sensor, it’s possible.

I think if I were you I’d have the oil analyzed at oil change to determine moisture content, if it’s high then I’d proceed with tape etc to raise it.

I’m not normally a big fan of oil analysis as people try to use it as an engine analysis, but for determining the condition of the oil it’s an exceptional tool as that’s in its name of course.

[M20F]

2 hours ago, Wallywingtip said:

No. but both the EDM and the primary are reading low, so we thought it real.

It is literally the easiest and cheapest thing, would try that first.  At least then you know what you are dealing with.

[Pinecone]

17 hours ago, carusoam said:

the CHTs, OAT, OilTs should all be reading similarly after being unused for a day…

And EGTs

[Guest]

I would question the installation of the probes, are both indicators sharing one probe. Heating the probes in a can of water with a thermometer would be a good first step.  

It’s also not impossible that the new vernatherm is defective.  

[Will.iam]

Doing some slow flight will heat up the oil and  cylinders especially if the cowl flap is closed. During winter my oil temps are low too on my 252 but a few minutes of slow flight brings the oil temp right up. 

[Wallywingtip]

On 3/27/2023 at 9:53 PM, Will.iam said:

Doing some slow flight will heat up the oil and  cylinders especially if the cowl flap is closed. During winter my oil temps are low too on my 252 but a few minutes of slow flight brings the oil temp right up. 

Thanks William. I'll give that a try next flight.

I checked the temps on both the OEM guage and the engine monitor when stone cold - both were at ambient.

Yes, two probes. The OEM probe is just before the oil cooler, and the engine monitor oil probe is in the galley block, and both read the same in flight yesterday, which was about 125 degrees F, and in the green. The ambient temp in flight at 6000 feet was minus 10C. A cool day, but not minus 40!

Looking at a previous (6months old) oil analysis, there is no water, emulsified nor free, in the oil. So, perhaps our concern around water remaining in the oil is ill advised. However, I still feel we should have warmer running oil temps.

Our mechanic is thinking we ought to inspect the 'seating' of the vernatherm when we pull it out to test it. 

Does anyone have experience with vernatherm seating issues?

Many thanks folks. 

[LANCECASPER]

56 minutes ago, Wallywingtip said:

Thanks William. I'll give that a try next flight.

I checked the temps on both the OEM guage and the engine monitor when stone cold - both were at ambient.

Yes, two probes. The OEM probe is just before the oil cooler, and the engine monitor oil probe is in the galley block, and both read the same in flight yesterday, which was about 125 degrees F, and in the green. The ambient temp in flight at 6000 feet was minus 10C. A cool day, but not minus 40!

Looking at a previous (6months old) oil analysis, there is no water, emulsified nor free, in the oil. So, perhaps our concern around water remaining in the oil is ill advised. However, I still feel we should have warmer running oil temps.

Our mechanic is thinking we ought to inspect the 'seating' of the vernatherm when we pull it out to test it. 

Does anyone have experience with vernatherm seating issues?

Many thanks folks. 

I think you're looking for a solution to a problem that doesn't exist. The indicated temperature is in the green range on your gauge and there is no moisture (milky color) in your oil, indicating that it's reaching a temperature somewhere in your oil flow (but not near the probe) that is high enough to take care of  the moisture. 

[Pinecone]

Also, the system was tested and reading 180 when the probe is in 212 water.

Then in flight, as long as reading is over 130, oil is at 162

[M20F]

18 hours ago, Wallywingtip said:

I checked the temps on both the OEM guage and the engine monitor when stone cold - both were at ambient.

 

I would use boiling water.  The probe may work at ambient but has issues as temps scale. 
 
This is my last post on the topic and agree with @LANCECASPER you seem desperate to try anything other than the advice given.  

[A64Pilot]

On 3/31/2023 at 6:46 AM, Wallywingtip said:

 

Does anyone have experience with vernatherm seating issues?

Many thanks folks. 

I did once but it was self inflicted. Only thing I can figure is when I changed Vernatherms the gasket stuck to the engine because I had two gaskets on it.

I was chasing what I thought was high oil temps and many hours later and bunches of money I finally discovered  nothing was wrong, that 200F in cruise on a HOT day isn’t bad.

You should see a slight shiny ring on the Vernatherm, but if your oil is always cold it’s very likely the Vernatherm never closes and may never fully seat, so in your case it’s likely you may not see that ring.

See here’s the thing, a Vernatherm when it closes forces all oil flow through the cooler, so one that doesn’t seat well will cause high oil temp, not low oil temp, and you have low oil temp.

Only way a Vernatherm could cause too cold oil temps is if it’s stuck extended and closed off the cooler bypass even when the oil is cold.

When oil is cold oil bypasses the cooler AND flows through the cooler, that’s why the cooler keeps some cooling no matter how cold it is, but as the oil gets hot the Vernatherm extends, closing off the bypass and making all oil flow through the cooler.

I have never seen a Vernatherm stick in the extended position, but it’s very easy to check, simply measure it’s length when room temp and removed.

I think you won’t find anything wrong, but take heart because an engine that runs low oil temp is one with little blow-by as blow-by tends to heat the oil.

I think if you want higher oil temps you will have to block air flow through the cooler, just ease into that of course.

[Guest]

12 minutes ago, A64Pilot said:

I did once but it was self inflicted. Only thing I can figure is when I changed Vernatherms the gasket stuck to the engine because I had two gaskets on it.

I was chasing what I thought was high oil temps and many hours later and bunches of money I finally discovered  nothing was wrong, that 200F in cruise on a HOT day isn’t bad.

You should see a slight shiny ring on the Vernatherm, but if your oil is always cold it’s very likely the Vernatherm never closes and may never fully seat, so in your case it’s likely you may not see that ring.

See here’s the thing, a Vernatherm when it closes forces all oil flow through the cooler, so one that doesn’t seat well will cause high oil temp, not low oil temp, and you have low oil temp.

Only way a Vernatherm could cause too cold oil temps is if it’s stuck extended and closed off the cooler bypass even when the oil is cold.

When oil is cold oil bypasses the cooler AND flows through the cooler, that’s why the cooler keeps some cooling no matter how cold it is, but as the oil gets hot the Vernatherm extends, closing off the bypass and making all oil flow through the cooler.

I have never seen a Vernatherm stick in the extended position, but it’s very easy to check, simply measure it’s length when room temp and removed.

I think you won’t find anything wrong, but take heart because an engine that runs low oil temp is one with little blow-by as blow-by tends to heat the oil.

I think if you want higher oil temps you will have to block air flow through the cooler, just ease into that of course.

He already stated that the temperature is cold even with the winter plate on the cooler.

[A64Pilot]

29 minutes ago, M20Doc said:

He already stated that the temperature is cold even with the winter plate on the cooler.

Yes I know and thought I explained how a vernatherm operates, and why one that didn’t seat won’t cause cold oil temps, that the only way that a Vernatherm could cause low temps that I can see is if it stuck extended, so in other words I think the Vernatherm is a red herring, and don’t be surprised if you don’t see a wear ring from being closed.

This winter plate, never seen one for a Mooney but assume it only partially covers the cooler? Others I’ve seen were that way.

I know several that Winter fly in the NWT etc and end up blocking the cooler even more than the winter kit does, and I know of more than one that has put a cable adjustable damper on the exit air of the cooler so they can adjust it in flight, but that’s an unsupported Mod so I wouldn’t suggest that, but using aluminum foil HVAC tape is also not legit, but I know it’s very frequently done too.

But bottom line if the oil is the proper viscosity for the temps and it’s not turning milky, and especially if analysis shows no water, what needs fixing?

[A64Pilot]

This gives a decent explanation of how a Vernatherm works.

https://www.kitplanes.com/a-verna-what/

Many think it’s like a cars thermostat, but it actually operates in the reverse in that as coolant in a car heats up a thermostat opens where as oil heats up a Vernatherm  closes, that’s why in a cold running engine whether the Vernatherm seat isn’t the problem.

[Wallywingtip]

Thanks very much folks. I appreciate all the advice.

Agreed, perhaps we don't have a problem. I'll report anything else we learn.