Cold Oil Temperature

[bpattonsoa]

I have had problems with keeping my oil temps up this winter. Originally I installed an oil cooler door, but removed it when it proved unnecessary. Now at around 500 hours, I was getting temps around 165 and water droplets on the dip stick.

I put the door system back in. In California style cold, (around 40-50) closing the door completely brings temps up to about 205, opening it 1/4" drops them to 180. So the "temperature Control Oil Cooler Bypass" the vernatherm must be leaking slightly.

I guess I could replace it, or does it just need removal and cleaning. My oil is changed a 25-30 hour intervals and filters every other change. If I need to replace, what is the current part number, my old engine parts catalog has 75944, but I saw another on the Internet.

Thanks

Bruce Patton
-6A 596S

 

[cross]

cool oil temps

Best check with an engine expert before replacing you varitherm valve. It's been my experiance that a little oil always flows through the oil cooler even when the oil is colder than 160 degrees. I suspect this my be intentional and perhaps they all behave this way. Even with my cooler compleatly blocked I couldn't get the oil up to 180 in cold weather untill I built winter fronts that got my cylinder temps up as well. If you run very long with low oil temps, it would probably be wise to change your oil more often.
Chuck Ross RV4 in Vernon BC Canada

 

[rvbuilder2002]

Best check with an engine expert before replacing you varitherm valve. It's been my experiance that a little oil always flows through the oil cooler even when the oil is colder than 160 degrees. I suspect this my be intentional and perhaps they all behave this way. Even with my cooler compleatly blocked I couldn't get the oil up to 180 in cold weather untill I built winter fronts that got my cylinder temps up as well. If you run very long with low oil temps, it would probably be wise to change your oil more often.
Chuck Ross RV4 in Vernon BC Canada

Chuck is correct. It is a by-pass as you mentioned, not a reroute. When the vernatherm path is open it provides a second path for oil flow but it does not shut off the primary path through the oil cooler. There is a residual flow through the oil cooler even when the vernatherm path is open.

It is very possible that you have a defective vernatherm. It is also possible that there is a problem with the seat that the vernatherm seals on (you didn't mention whether you had an overhauled, new, midtime, high time engine, etc.) There is a special tool that can be used to reface the seating surface if it is damaged or worn unevenly.

Is it possible that you are not running a very high power setting? A lot of us loaf our engines when just cruising around ( high fuel prices!) and this can have a large effect on oil temp.

 

[tin man]

Not sure if your oil cooler door is restricting the incommong air or the outgoing air. Restricting the incomming air is more efficent than the outgoing. I have a simple oil cooler installation. It is mounted behind one of the rear cylinders with an inlet hole to the cooler plenum. During the winter (California) I put a reducer on the rear baffle that cuts down approx 50% of the inlet area. Its worth 20 to 25F degress of oil temp.
YMMV
tin man

 

[bpattonsoa]

The engine was new from Vans. The oil cooler is firewall mounted with a 3" duct to the rear baffel to the cooler. A flapper valve is mounted on the baffel with a cable to the cockpit. I don't like it because the flapper vibrates in the air flow when almost closed, (where it has to be to control the oil at around 180). I don't llike my design of the door and am worried about it failing closed. The air pressure would definately keep it closed. A better design would have the door on the outlet of the cooler so failures would be to increase air flow.

The overcooling issue did not show up until this winter. Therefore I am assuming that something has happened to cause more oil flow to the cooler at low temps. I also noted the presence of drops of condensation on the dip stick. That is why I put the oil door back in. By shutting the door completely for a time near the end of a flight I can run the oil hot enough to drive out the moisture. I do oil analysis with every other oil change, and have never seen any abnormal results.

Bruce

 

[Mel]

How about.....

leaving the door on the baffle but redesigning it to be a sliding door? This would give you better control and eliminate "flutter" of the door.

 

[David-aviator]

I have had problems with keeping my oil temps up this winter. Originally I installed an oil cooler door, but removed it when it proved unnecessary. Now at around 500 hours, I was getting temps around 165 and water droplets on the dip stick.

I put the door system back in. In California style cold, (around 40-50) closing the door completely brings temps up to about 205, opening it 1/4" drops them to 180. So the "temperature Control Oil Cooler Bypass" the vernatherm must be leaking slightly.

I guess I could replace it, or does it just need removal and cleaning. My oil is changed a 25-30 hour intervals and filters every other change. If I need to replace, what is the current part number, my old engine parts catalog has 75944, but I saw another on the Internet.

Thanks

Bruce Patton
-6A 596S

Bruce,

I'd venture your system is working just fine, I wouldn't do anything with it.

The vernatherm is not a thermostat. When temps get hot it closes the engine port and forces all oil through the cooler, otherwise it is an open Y, oil can flow through the cooler of go back to the engine. There is no way you can close off oil flow to the cooler. It is an ingenious design and has been so for many years. That's why the cooler has to be blocked in cold weather. Certified aircraft like the Cherokee require the cooler be blocked at OAT's less than 30F.

 

[rvbuilder2002]

The engine was new from Vans. The oil cooler is firewall mounted with a 3" duct to the rear baffle to the cooler.

The overcooling issue did not show up until this winter.
Bruce

A remoted cooler is quite efficient when fed with a 3" SCAT (better than some installations on the rear baffle) as long as the SCAT doesn't make a bunch of sharp turns getting to the cooler. The vernatherm only regulates the temp. within a narrow temp range. If the OAT is below or above this range you will see a corresponding decrease or increase in oil temp (from normal).
It is not unusual (pretty typical actually) for the oil temp on an RV to run cool in the winter (particularly in more northern areas).
Some sort of block off for the cooler is a good way to deal with it. blocking the air into the cooler (as you are doing, is more effective than blocking it on the outlet side.

leaving the door on the baffle but redesigning it to be a sliding door? This would give you better control and eliminate "flutter" of the door.

I agree with Mel. Change it to a sliding door. Vans sells one that is meant to cover the entire front of an oil cooler (probably not what you need since you feed your air through a SCAT hose) but you may be able to adapt the idea.

Bruce,

I'd venture your system is working just fine, I wouldn't do anything with it.

The vernatherm is not a thermostat. When temps get hot it closes the engine port and forces all oil through the cooler, otherwise it is an open Y, oil can flow through the cooler of go back to the engine. There is no way you can close off oil flow to the cooler. It is an ingenious design and has been so for many years. That's why the cooler has to be blocked in cold weather. Certified aircraft like the Cherokee require the cooler be blocked at OAT's less than 30F.

I concur with David (same as what I was describing in my previous post). I didn't want to assume you don't actually have a problem with your vernatherm/bypass system (is still possible but not very likely). A test for that will be whether it still cools properly after the temps start getting hot again.

 

[kcameron]

I always wondered

... if the vernatherm could be improved. I should be possible to design a system that diverts oil between the cooler and the bypass depending on temperature while ensuring that oil to the engine is never blocked. It seems doable and would quicken warm-up time for everyone while eliminating the need for restrictor plates or pilot controlled valves in cold climates.

 

[bpattonsoa]

leaving the door on the baffle but redesigning it to be a sliding door? This would give you better control and eliminate "flutter" of the door.

Mel

That sounds like the best solution. The operating cable can stay almost as is, and a small slider would be failure proof.

Til then I will continue closing the door completely near the end of the flight and dry out the oil, then reopen at letdown. When California returns to normal temperatures, I can just ignore the situation, it always has worked well in warm temps.

Unfortunately (?) I am having to fly too much to have time to convert to a slider. Maby next winter.

Thanks all,

Bruce