Oil temperature again!

[vinzer]

Hello All!

I have a question about the oil temperature in my RV10. I conducted an extensive run-up on the ground and pushed it the way so my highest CHT went to 410°F for a minute, while all other CHTs ranged from 380°F to 410°F at the same time. The oil temperature rose to 218°F. After setting the engine to nearly idle and leaning, I waited. Within 5 to 10 minutes, the CHTs decreased to 320°F ... 350°F range, but the oil temperature remained at 218°F with no change. Taxing back to the hangar took another 7 to 10 minutes, and by the end, the oil temperature was still 217°F.

I understand that CHT and oil temperature are different parameters and cylinder cooling is way much faster process, but I expected the oil temperature to correlate with the CHTs in some way. The engine is an IO-540, the oil temperature sensor is tested and serviceable, and the oil cooler is a standard one (I believe 11 rows), which is the default for this kit from VANs. The oil cooling hose at the back of cylinder 6 is not obstructed.

I've always had the oil temperature on the high side but never checked it on the ground. Is this behavior of the oil temperature normal for such conditions , or should I start checking the venatherm ?

Almost forgot to add here: after some time I removed the cowl and measured temperatures on the surface of the oil filter and inside of the oil cooler's fins.
The oil filter surface is 152F and and oil cooler fins are 108F. Again I understand that oil filter cools slower but oil cooler still contains a hot oil so temperature difference should not be that much, should it ?

 

[TLockard]

Hello All!

I have a question about the oil temperature in my RV10. I conducted an extensive run-up on the ground and pushed it the way so my highest CHT went to 410°F for a minute, while all other CHTs ranged from 380°F to 410°F at the same time. The oil temperature rose to 218°F. After setting the engine to nearly idle and leaning, I waited. Within 5 to 10 minutes, the CHTs decreased to 320°F ... 350°F range, but the oil temperature remained at 218°F with no change. Taxing back to the hangar took another 7 to 10 minutes, and by the end, the oil temperature was still 217°F.

I understand that CHT and oil temperature are different parameters and cylinder cooling is way much faster process, but I expected the oil temperature to correlate with the CHTs in some way. The engine is an IO-540, the oil temperature sensor is tested and serviceable, and the oil cooler is a standard one (I believe 11 rows), which is the default for this kit from VANs. The oil cooling hose at the back of cylinder 6 is not obstructed.

I've always had the oil temperature on the high side but never checked it on the ground. Is this behavior of the oil temperature normal for such conditions , or should I start checking the venatherm ?

Almost forgot to add here: after some time I removed the cowl and measured temperatures on the surface of the oil filter and inside of the oil cooler's fins.
The oil filter surface is 152F and and oil cooler fins are 108F. Again I understand that oil filter cools slower but oil cooler still contains a hot oil so temperature difference should not be that much, should it ?


View attachment 71516

I have an RV-10 with the standard oil cooler from Vans as well. I always have rising oil temps on taxi and even see a rise when at low power and slow flight Like in the pattern. I had an episode on an IFR departure where the procedure was to wait until you were first in line to depart then click the radio to get ATC to call you. Unfortunately everyone started just calling them on the phone and I was left idling on the taxiway to get a clearance. Even pointed into what little wind there was the oil temp finally reached 220 and I had to shut down and wait for it to cool down some. Even after getting a clearance by the time we departed it was back in the upper 210’s but as soon as we were airborne with some good airflow through the cowl the temps were declining and in cruise usually are below 200

I don’t know how the surface temperatures between oil cooler and oil filter compare so can’t make any comments on that, but to me it sounds like your ground temps compare to what I see on the ground.

TLockard

 

[Scott Hersha]

Hello All!

I have a question about the oil temperature in my RV10. I conducted an extensive run-up on the ground and pushed it the way so my highest CHT went to 410°F for a minute, while all other CHTs ranged from 380°F to 410°F at the same time. The oil temperature rose to 218°F. After setting the engine to nearly idle and leaning, I waited. Within 5 to 10 minutes, the CHTs decreased to 320°F ... 350°F range, but the oil temperature remained at 218°F with no change. Taxing back to the hangar took another 7 to 10 minutes, and by the end, the oil temperature was still 217°F.

I understand that CHT and oil temperature are different parameters and cylinder cooling is way much faster process, but I expected the oil temperature to correlate with the CHTs in some way. The engine is an IO-540, the oil temperature sensor is tested and serviceable, and the oil cooler is a standard one (I believe 11 rows), which is the default for this kit from VANs. The oil cooling hose at the back of cylinder 6 is not obstructed.

I've always had the oil temperature on the high side but never checked it on the ground. Is this behavior of the oil temperature normal for such conditions , or should I start checking the venatherm ?

Almost forgot to add here: after some time I removed the cowl and measured temperatures on the surface of the oil filter and inside of the oil cooler's fins.
The oil filter surface is 152F and and oil cooler fins are 108F. Again I understand that oil filter cools slower but oil cooler still contains a hot oil so temperature difference should not be that much, should it ?


View attachment 71516

Vinzer,
I think what you experienced, relative to oil temperature indications, are normal and what I would expect to see. Oil temp not only takes a longer time to react, but at low RPM while taxiing, you have little cooling airflow through your oil cooler. You are pumping maybe 8-9 quarts of oil through a hot motor at reduced RPM and reduced oil flow rates through an oil cooler that is not doing much because of little airflow through it. I wouldn’t expect to see a very drastic difference in oil temperature after it’s hot on the ground while the engine is running and still some producing heat, even when leaned at low RPM. In that situation the oil is the primary coolant since the only other coolant - air - is almost non-existent.

 

[vinzer]

Vinzer,
I think what you experienced, relative to oil temperature indications, are normal and what I would expect to see. Oil temp not only takes a longer time to react, but at low RPM while taxiing, you have little cooling airflow through your oil cooler. You are pumping maybe 8-9 quarts of oil through a hot motor at reduced RPM and reduced oil flow rates through an oil cooler that is not doing much because of little airflow through it. I wouldn’t expect to see a very drastic difference in oil temperature after it’s hot on the ground while the engine is running and still some producing heat, even when leaned at low RPM. In that situation the oil is the primary coolant since the only other coolant - air - is almost non-existent.

Hey Scott,
Thank you for your reply and details provided. I totally agree about reduced oil flow and little to none airflow to cool it. I have experienced my abnormal oil temperatures from day one. In the hot summer days 225F was the norm which obviously is not.
I found something else interesting: I went ahead and removed the venatherm, placed it in the water and boiled it. Venatherm did not even move - I measured the length prior on cold and then right after removing from boiling water - identically the same.
Not sure if hot oil will make a difference but boiling water failed the test.

 

[BH1166]

Hey Scott,
Thank you for your reply and details provided. I totally agree about reduced oil flow and little to none airflow to cool it. I have experienced my abnormal oil temperatures from day one. In the hot summer days 225F was the norm which obviously is not.
I found something else interesting: I went ahead and removed the venatherm, placed it in the water and boiled it. Venatherm did not even move - I measured the length prior on cold and then right after removing from boiling water - identically the same.
Not sure if hot oil will make a difference but boiling water failed the test.

If i recall, stuck closed, which I believe it would not circulate through oil cooler. I pulled mine once, tested as you did, very visible when it popped open/lengthened.

 

[mburch]

I found something else interesting: I went ahead and removed the venatherm, placed it in the water and boiled it. Venatherm did not even move - I measured the length prior on cold and then right after removing from boiling water - identically the same.
Not sure if hot oil will make a difference but boiling water failed the test.

That's a telling result - you should be getting something like ~0.2" of extension at boiling temperatures. Oil or water makes no difference.

If i recall, stuck closed, which I believe it would not circulate through oil cooler.

Dan H has a good explainer of the Lycoming oil system: https://vansairforce.net/threads/lycoming-accessory-case-oil-schematic.45548/

The short version is that some amount of oil always goes through the cooler, and there is a second passage that allows oil to bypass the cooler. When hot, the Vernatherm extends and blocks the bypass, thus forcing all the oil to circulate through the cooler instead of just "some". The Vernatherm can never block the oil cooler, but a weak or dead Vernatherm will result in less than the full amount of oil going through the cooler when it otherwise should.