Excessive oil cooling

[Draker]

Now that it's cold where I am (well at least California-Cold, which is not really cold as our midwestern friends will remind me) I'm seeing pretty low oil temps. It'll bottom out around 155F in cruise, in ~8C,45F OAT, but I have once seen an oil temp as low as 145F (similar OAT). This is consistent with what I observed during my initial flight tests last year, so nothing has recently changed.

Lycoming's operating manual for my engine recommends several desired oil temperatures from 160F to 180F depending on ambient air temperature, and includes a note that oil should not be below 140F during continuous operation. And my understanding is that our oil systems include a vernatherm that opens and closes in order to regulate oil temperature by forcing it through the cooler when it gets hot (and presumably also blocks it from the cooler when it gets cool). Does the vernatherm require adjustment as the weather changes?

There are a couple of threads describing adding a pilot-controlled shutter onto the oil cooler, to block off the airflow when the oil is not warm enough. Looks like a few of the usual vendors including Vans sell these shutters. But what purpose do these shutters serve with the vernatherm controlling oil flow? Shouldn't the oil flow through the cooler be at a minimum if the oil itself is cool?

I suppose my oil temperature probe may be inaccurate too. Any good tips on how to measure its accuracy?

 

[BH1166]

Ryan, what is cht egt after shutdown 24hours + compared to oil temp? I found mine not matching. I agree with cht and egt based on hangar temp, not oil temp ever. Mine always 10-15 degrees higher than cht egt which match to each other.

 

[Draker]

Ryan, what is cht egt after shutdown 24hours + compared to oil temp? I found mine not matching. I agree with cht and egt based on hangar temp, not oil temp ever. Mine always 10-15 degrees higher than cht egt which match to each other.

Oh, duh, why didn't I think of that? Looks like reasonably close. CHT 59F, EGT 55F, OIL 58F. So at least at room temperature there doesn't seem to be a sensor problem. Thanks for the tip.

 

[mfleming]

I too have low oil temps when it's cool out. I put a plate on my oil cooler that covered about 1/3 of it. That didn't affect my oil temps in the slightest.


I'm thinking of increasing the size of the plate but haven't got to it yet.

 

[bjdecker]

Vernatherm's will have a number stamped on them -- In both of my aircraft it's 86C -=> 86°C -=> 186.8°F. If I see oil temps below 186°F (give/take) I know that there's not a lot of oil moving through the cooler.

Verify your oil temp by bringing a pot of water to a boil and then drop the sensor in it -- it should read ~212°F on the EFIS --- adjust for pressure effects (higher field elevations = lower boiling point of water).

 

[Mikeyb]

Low oil temp is common with the parallel valve IO360. The Vernatherm doesn’t stop all the oil from going through the cooler. Even with the exit of the cooler completely covered with metal tape the temperature still runs below the Vernatherm setpoint in this weather.

I did verify my oil temp sensor is accurate. Mine is an Westach. The resistance/temp data attached. You can verify the resistance by disconnecting one wire from the instrument and measuring with an ohmmeter. Probably not necessary.
Mike

 

[rvbuilder2002]

Vernatherm's will have a number stamped on them -- In both of my aircraft it's 86C -=> 86°C -=> 186.8°F. If I see oil temps below 186°F (give/take) I know that there's not a lot of oil moving through the cooler.

But there is always some flow through the oil cooler which is why blocking airflow through it does raise the oil temperature.

 

[Bavafa]

My experience with my RV7A was the same as with Mike (Mikeyb) and I live about 10 minutes from Ryan, so same environment. I end up installing a shutter which I could control from the cockpit, problem solved.

 

[RV8JD]

I've applied AL foil tape on the front side of the oil cooler so I can fold it up or down, depending on the season and how much of the cooler I want to cover. You may have to unbolt the cooler so you can get the AL foil tape all the way down to the bottom of the cooler, since the cylinder is in the way otherwise.

I'm on my second RV-8 in the Pacific NW. The first one had a parallel valve IO-360-A1A with 10:1 HC pistons and LASAR EIs. My current RV-8 has a parallel valve IO-360-M1B with a Slick IC Mag and an LSE Plasma III EI. Both airplanes have the oil cooler mounted behind Cylinder #4. Both airplanes have versions of Hartzell CS props.

Both airplanes have to have the front side of the oil cooler blocked off with AL tape to some degree to keep the oil temps between 165° F and 200° F in cruise.

On my current RV-8, in the winter most (~90%) of the front side of the oil cooler needs to be covered. In the summer, about 40% - 50% needs to be covered. My previous RV-8 was similar.

I found that blocking the backside of the cooler with a piece of AL plate bolted to the back via the mounting holes does not help much to increase the oil temp (~10° F), since air still flows around the tubes.

The minimum oil temp per Lycoming for continuous operation is 140°F. Desired oil temp is between 180°F and 190°F. I'm happy with anything between about 165°F and 200°F.

 

[Draker]

Interesting, Carl. I did try the metal tape last winter, but not that much, maybe 1/4-1/3 of the surface area covered. I was hesitant to even cover that much. You covered a lot of it!! This might be interesting to experiment with.

 

[rv8ch]

I got the temp up on mine by fully blocking the oil cooler up front. Nothing else made much difference.

What I'm still struggling with is the recommended temps. I know it was carved in stone many eons ago, but is there science/data that says we need to get the oil to 180F? Even in the Lycoming chart, they say min 160F.

Clearly the oil needs to flow freely - that's pretty much assured at anything over 100F, particularly with a multi-weight oil.

We know combustion creates water - that will mostly go out the breather, and true, some will get into the oil. I understand that the basic idea is hot oil will evaporate the water.

A glass of water will evaporate at room temp, and I'd guess that the oil splashing around will see very high temps at some point, and if there is any moisture it will become a gas, and go out the breather.

Will higher temperature prevent a "buildup" of moisture in the oil?

I do engine oil analysis on each change, and Blackstone has never found any water in my oil. I also keep my engine on an engine dryer when in the hangar - perhaps if I didn't do this, Blackstone would find water?

I wonder if we are dealing with an OWT, since typically we're trying to keep things cooler in our engines, and it seems counterintuitive to not take advantage of the cooling capability of the oil.

 

[MacCool]

When I bought my airplane home, I noted low oil temps....130 degrees F on a typical November day. An AntiSplar oil shutter between plenum and oil cooler solved that problem, and their Bowden cable assembly made it easy to control from inside the cockpit.

 

[Dan 57]

several threads on this subject...

My firewall mounted cooler is fed by a 2 1/2 Scat, and is probably over dimensioned.

Seeing temps in 160 range in Winter, I installed a shutter (shown closed with the Scat removed) which ended up selected fully closed for most of the year, but rare days when OATs >35°C. The shutter improved Ts somewhat so that, but on the coldest of days, a T of 180 can be reached and maintained, despite using low power cruise settings.

 

[JonJay]

Be aware that the lever to shutter interface is two small steel pins rotating in bare aluminum holes.
Mine lasted 900 hours, pretty good, before the steel pins wore the aluminum holes and the shutters no longer actuated. You can take it apart and put new shutters in, but I chose to just do the metal tape and removed the shutter and associate cable. Worked great, until then.
Mine looked identical to what Aerosplat offers, but bought it from Vans many years ago. Not sure who made it.

 

[RVDan]

“and presumably also blocks it from the cooler when it gets cool”

This is not correct. The passage to the oil cooler is always open. When the oil is hot, the vernatherm closes blocking the case ports and forcing oil through the cooler.

This arrangement allows some small amount of oil to flow through the cooler, possibly preventing congealing of stagnant oil in the cooler.

It is also why an air blocking device is required with cold OATs.