Blocking off Oil Cooler in cold weather

Skystrider · Post by **Skystrider** » Tue Dec 09, 2008 12:57 pm

For the last couple of years I have been using duct tape to close off the air flow to the oil cooler when the weather gets really cold. Seems like there should be an aftermarket device to do that in a more elegant fashion. Anybody heard of such a thing?

Hottshot · Post by **Hottshot** » Tue Dec 09, 2008 4:27 pm

Yes ther is a "Gate" type of cooler block off I will try to get pictures again. Bob Hoff was puting them on the Huskies and there is another that the RV guys use as well.

210TC · Post by **210TC** » Tue Dec 09, 2008 5:56 pm

I have never operated in the conditions you guys up north do. However, why do you not have a bypass so the oil does not enter the cooler, but rather goes around and back to the engine? This is not uncommon on other applications.

Hottshot · Post by **Hottshot** » Wed Dec 10, 2008 8:29 am

210TC wrote:I have never operated in the conditions you guys up north do. However, why do you not have a bypass so the oil does not enter the cooler, but rather goes around and back to the engine? This is not uncommon on other applications.

Good question...

a64pilot · Post by **a64pilot** » Wed Dec 10, 2008 8:44 am

The vernatherm is the oil cooler bypass. It works directly opposite of an automotive thermostat in that heat causes it to expand and close off a passage that then forces all of the oil through the cooler. When the oil is cold the vernatherm is short which allows oil to both bypass and flow through the cooler keeping warm oil in the cooler.
You don't want to bypass the cooler because then the oil in the cooler will become very cold and viscous. Then when the bypass were to open you would either get almost no oil flow or a thick cold slug of oil from the cooler into the hot engine.
It's easy to fashion a door like a carb heat door to block off air through the cooler and make it cockpit adjustable just like the carb heat. A lot of the old radial engines had adjustable airflow through the oil cooler just like a lot of airplanes have cowl flaps. It's easy and nothing new, but apparently getting something like that field approved isn't easy. Actually it wouldn't be hard to make it fully automatic using a thermostat type of spring like you used to see in the airfilter housing of old cars, you know the ones that when it was cold closed off a door from the intake snorkel and forced the air to come from a shroud form around the exhaust manifold, but then automatically opened when the under the hood temps got warm?
Just try getting that approved though.

Experimental starts looking better and better.

Hottshot · Post by **Hottshot** » Wed Dec 10, 2008 9:26 am

a64pilot wrote:The vernatherm is the oil cooler bypass.

Just try getting that approved though. Experimental starts looking better and better.

HA!! Veratherm I knew there was something as we have adjusted it in the past on other planes. and I hear the Experimental thing!!!

Skystrider · Post by **Skystrider** » Wed Dec 10, 2008 10:43 am

Hey Wup, Yeah, I would like to see a picture of that device. Do you know if this is something Bob has STC's for on the Huskies?

denningte · Post by **denningte** » Mon Dec 15, 2008 9:15 pm

There is an STC for the Husky. I do not know if Gate 9 is going to extend it to other planes. I have pictures of the approved model and a couple of knock-offs. This mod relates to engine cooling and is by FAA definition a mod that has to be approved. Tennis balls and duct tape do not.

TD

belandd · Post by **belandd** » Mon Dec 15, 2008 9:48 pm

Does it get cold in Penn?

I don't know if blocking off the cooler in the cold is a good idea or not. I don't fly if it is more than 10 below.

Just too cold in the cockpit.

Let one of the more experienced Alaska guys give some advice here.

UP-M5 · Post by **UP-M5** » Tue Dec 16, 2008 9:05 am

it was -5 to -10 this weekend and i got middle of the green on oil temp with the cooler totally blocked with aluminum foil tape. it peels off better than duct tape.

Hottshot · Post by **Hottshot** » Tue Dec 16, 2008 9:13 am

UP-M5 wrote:it was -5 to -10 this weekend and i got middle of the green on oil temp with the cooler totally blocked with aluminum foil tape. it peels off better than duct tape.

That is what we use as well!

aero101 · Post by **aero101** » Tue Dec 16, 2008 5:00 pm

Ditto!!!

Post by **andy** » Wed Dec 17, 2008 4:26 pm

I'd really like to see a gated oil cooler that you can operate from inside the cockpit. I have an aluminum plate that blocks about 1/2 of the oil cooler but it's a pain to install or remove. Our winter temperatures vary as much as 30 degrees in a day and this week they were in the high 50s and low 60s. It drove me crazy installing and removing the oil cooler baffle every time the temperature rose above 40 degrees last year, so I decided not to install it this year. I'd be a candidate for one of the gated ones.

Andy

aero101 · Post by **aero101** » Thu Dec 18, 2008 10:11 am

I don't think I'd worry about blocking the oil cooler up when airtemps above +10F as the vernatherm will adequately control the oil cooler at those temps. Vernatherm doesn't normally route oil thru the oil cooler if it's working properly until oil temp in the 180F - 200F range and you don't really have a problem with oil congealing above 0F anyway if you're running a multi viscosity oil? Where it's really neccesary is when outside temps way down like to -20F range, if the vernatherm pops open the oil cooler and a big slug of super cold / pressurized oil tries moving too quickly. It can actually blow a oil cooler apart, but it's got to be very cold air temps to do so? If you're not blocking off cooling air in another manner, your engine oil temp probably hovers in the 160F range and oil cooler will not be cooling any oil? I know people up here that don't block oil cooler all winter long in these cold temps, but they do reduce the cooling air inside cowl in one form or another to prevent shock cooling, etc, etc... When the vernatherm opens as oil temps increase, it does so in a fairly slow manner, so the cold oil is slowly mixed with the warm so long as the oil is not congealed...

a64pilot · Post by **a64pilot** » Thu Dec 18, 2008 2:07 pm

The vernatherm opens when cold and closes when hot, just opposite of what we think of, especially when we try to compare it to a car thermostat.
The vernatherm is essentually in the middle of a Y connection. One leg of the Y is oil pressure from the pump and one leg is the cooler and the other leg bypasses the cooler. So when it's cold the Vernatherm is open and oil flows both through the cooler and through the bypass so warm oil is always flowing through the cooler and being cooled, no matter how cold it is.
When the oil is hot, the Vernatherm closes off the bypass and one leg of the Y is closed so ALL of the oil is routed through the cooler.
It's this reason that blocking off airflow through the cooler works in cold weather because there is always oil flowing through the cooler no matter how cold it is.
Cold weather can cause the oil viscosity to be so high that even though the oil pressure relief valve opens, it can't dump enough oil to keep the pressure from skyrocketing and yes it's usually the cooler that is the weak link. I'd rather blow an oil cooler than spin a bearing though.
The oil pressure relief valve has to be designed so that if it were to stick in the open position there would still be enough oil pressure to keep the engine running so that's why your oil pressure can sky rocket with cold oil.
I still don't know why ther is no adjustable oil cooler air door, I can be trusted to operate cowl flaps, what's the difference?
I run higher than I like oil temps in the summer, but in cold weather I'm blocking off the cooler.
What would make the most sense would be to fit the 260's bigger oil cooler to keep me nice and cool in the summer and have a cockpit adjustable air door to keep my oil warm in the winter. That way I could always have oil temps between 180 and 200. Too simple huh?

Blocking off Oil Cooler in cold weather

Blocking off Oil Cooler in cold weather

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