What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

If the thermostat inside the oil-cooler fails, does it go to full open?

A

ao.frog

Well Known Member
Hi gang.

I have the Stewart Warner oil cooler on the baffle behind cyl # 4 (IO-360) per Vans plans.
In front of the cooler, I have installed the oil cooler shutter from Vans.

Up until now, (210 hrs) it's been working ok, but Fall has come to Norway now, and the OAT's are dropping.

During the last few flights, I have noticed that I'm not able to keep the oil-temp to where it has been up until now; 180-200*F during cruise.

Temps are in the 150-160*F range with OAT's around 35-40*F and a powersetting at 55% (21/2100).

So far, it looks like the oil temp is dropping along with the OAT as they are getting lower.

For example: I can take off on the first flight of the day with the shutter fully closed and a oil-temp around 100*F and increasing.
Then, at for example 5000', the oiltemp is 180-190 and when reducing to cruise-setting, the oil-temp start dropping to the 150-160 range.

This is NOT the way the oil temp has been during low OAT's before, because the shutter has always been able to keep the oil-temps up, even on low powersettings.

Therefore I'm wondering if anything has happened with the oil-cooler.
It has some kind of thermostat inside, right? Vernaterm valve or something?

I think I've read somewhere that this valve in the cooler never goes to fully closed; there's always some oil flowing past the valve, even in low OAT's.

But seeing that I'm not able to keep up then temps like before, I'm wondering if that valve has failed to full open? Or is such a failure not possible?

I don't have a clue of the inside of a cooler, but hopefully there's someone out there who knows more than me about this.

What I do know however, is that something prevents the oil-temps to be in normal range. I've not had any problems keeping the oil temp up during the last three winters I've had the RV.

Any good ideas where to start looking?
 
Alf,

Your system is perfectly normal.

Lycoming controls oil cooling, to a point, with the device commonly known as the vernatherm. (the official name is oil cooler by-pass valve)

The valve does not cause oil to by-pass the cooler, the port to the cooler is always open. The valve sits at a Y junction where oil can flow to the cooler or back into the engine. When oil is hot, the valve closes the port to the engine and oil is forced through the cooler. If the valve fails, the port to the cooler is always open. The port to the engine may be blocked but the port to the cooler is always open.

With certified aircraft the oil cooler is covered with a plate below a certain temperature to block air flow through it. With the Cherokee 180, I believe the cover is installed at 30F and below.

Your best option is find a way of blocking air flow through the oil cooler for cold weather operations. I have an air shutoff valve but even with it full closed, on a cold, cold day, the oil temp may not come up to 140. In cold climates, I believe there also is a method of blocking air flow across the cylinders to get CHT's up which will also increase oil temperature.

Oil coolers do not have built in thermostats.
 
Shutter installed

Hi David.

Thanks for the reply, but I probably didn't use the correct words, because I think you misunderstood me: I already have a system for blocking air to the cooler: the Vans oil cooler shutter. See pics below.








This shutter has performed great for three winters now.

Based on what you are writing above: maybe it's possible that the valve you are mentioning now has failed on my cooler and that the oil is always flowing through the cooler?

That could explain why I'm not getting the oiltemps up, even with the shutter fully closed (no air into the cooler)

I know that SOMETHING has changed since last winter, because back then I had no problems keeping the oil temps up....
 
Test or have someone test your vernatherm

Mine is below oil filter. When heated in an oil bath to 180-190F it should extend. If yours is stuck in the extended position closing off the port to engine then all of your oil goes through oil cooler. Even with no airflow your uninsulated cooler still makes a good heat exchanger.

Also compare the oil cooler temp to engine oil sump temp immediately after a flight. If they are the same then your getting too much flow through cooler.

You can also use two thermistor sensors, one just in front and one in rear of cooler to check temperature rise(with shutter open). If it is more than a few degrees then your getting too much flow.
 
You're correct, Alf, I did not completely understand the situation.

Something has changed since previous winters, that's for sure.

I've read the only sure way to control oil temp in cold weather is to have shut off valve in the line to the cooler. The guy who wrote that piece has such a valve controlled from the flight deck. It's a brass ball valve of some sort.

Could be the vernatherm is stuck in the engine port.
 
There is no valve inside the cooler body.

Oil always flows through the cooler. An extended (hot) vernatherm merely closes the cooler bypass.

2n703f9.jpg
 
Last edited:
Thanks for the drawing Dan.

If I understand that drawing correctly, then the vernatherm valve is mounted somewhere outside the cooler then? maybe somewhere below the oilfilter?

Maybe underneath the big silver-coloured nut just below the oilfilter on this pic? (the one that is safety-wired)

 
ao.frog said:
Maybe underneath the big silver-coloured nut just below the oilfilter on this pic? (the one that is safety-wired)
Click to expand...

That's it! The vernatherm is under that nut.

On the RV-8 in my avatar, I did something a little different that most folks do to get the oil temps up in winter... I made a hinged door on the rear of the oil cooler to block off airflow, that is opened and closed by an electric servo motor (actually a Ray Allen trim servo). It's worked quite well in as low as 20F OAT. In the summertime, we have to remove the door completely to ensure enough air goes thru the cooler to keep the oil temps down...

Pics in this thread: http://www.vansairforce.com/community/showthread.php?t=66901&highlight=oil+cooler+door

Edited to add: Vernatherms rarely ever fail in the full-extended position (which would force most of the oil to flow thru the cooler). Most often, they fail to extend fully, or seal fully, which will cause less oil to flow thru the cooler, and result in higher oil temps.
 
Last edited:
What Dan said (excellent picture)! The large silver nut is the top of the Vernatherm. It will extend by about 1/4" when its hot - take it out, measure it and dunk it in boiling water and re-measure. Also check your temperature gauge, the sender is just a resistor - ask the gauge manufacturer what the cold and hot values are.

Pete
 
Thanks for the replies guys. I've learned alot today! :)

Guess I'll make a mess if I take that valve out without draining the oil, so I guess that draining schould be done first.

Then measuring the length both when I get it out and then in boiling water. Great idea!

Gotta love this forum.... :)
 
Alf,
My own adventures in vernatherm checking here:

http://www.vansairforce.com/community/showpost.php?p=536959&postcount=12

I doubt it can fail in the extended position, but hey, can't hurt to check.

More about the oil circuit here:

http://www.vansairforce.com/community/showthread.php?t=45548&highlight=schematic

I know that SOMETHING has changed since last winter, because back then I had no problems keeping the oil temps up....
Click to expand...

Just for fun I'll throw in two "normal" possibilities. One is that you had a baffle seal leak, and it molded itself into compliance during the summer. Increased upper cowl pressure would result in more mass flow through the cooler. The other is reduced combustion gas blow-by due to improved ring seating. Blow-by is a big factor in oil temperature.

Do you mind if I copy it for my Pilot Manual?
Click to expand...

Thanks for asking Bob. Yes, you may....I drew it for the public domain.
 
Last edited:
loose connection

Good information so far. My little suggestion would be to verify that your fasteners are all still tight. The Van's adjustable vents I am familiar with are adjusted by Push-Pull cable and I am wondering if the connection has loosened to allow it to slip and the vents to not close. It may even function correctly while on the ground because it does not have the air pressure behind it, but if it is loose then once you are in the air and it has the air pressure on it then the connection may be slipping and not closing.

Good luck.
jackson
 
While we are on the subject of oil cooling, I just removed my aft closing shutter and installed Vans shutter in the front. I am just hoping that it is not too restrictive in a fully open position and will get adequate cooling in the summer time. With a aft closing shutter, I flew all summer long with no heating issue.
 
An update

Hi guys.

This is a follow-up to my previous post:

During last winter, I had low oiltemps (130-160*F) basically all the time. They varied some due to powersettings and OAT's, but it was not possible to get them above 180*F at all until OAT's increased this spring.
I had the Vans Oil cooler shutter fully closed all the time.

I'm just done with annual, and I took the oppurtunity to remove the Vernatherm, examined it and measured it in room-temps and in boiling water.


Here's a pic in room temp. Total length 95 mm (approx 3 and 3/4 inch)






And here's how it looked after a few mins in boiling water. Total length 102 mm (approx 4 inches 1/32)





I also removed the Vernatherm from the Lyc IO-360 I'm building right now (the other one is from my flying -7) to have something to compare with, and they behaved more or less exactly the same way those two Vernatherms.

Here's a pic where one is cold (the short one) and one has just been removed form boiling water (the extended one)





Here's the back side of them both:





So there you have it folks: what schould I do as the next step?
BTW: I have checked the oil-temp gauge and sender and they seem perfectly fine to me, both regarding what they show and how they look and behave during flight.

There must be SOMETHING that prevents the oiltemps from getting up to the normal temp-range.
Any suggestions?

Thanks :)
 
Air flow is the key

Where are your CHT's. If they too are low you can cut down on the inlet air. I live in Minnesota and it is common in the winter to block off part of the inlets with duct tape. Sometimes as much as half is blocked.

The other thing is to make your engine produce more heat by increasing your power setting. When it gets cold your engine struggles to get warm enough to boil off moisture from the oil.

The ironic thing is I am writing this and it is 99 degrees F out. Good luck

Gary Specketer
 
Thanks for chiming in Gary.

The CHT's has mostly beetween 275 and 375*F (aproximate) depending of OAT's and powersetting.
During high powersettings (takeoff and acro) during summer, the CHT's have been at 400*F +/-

The thing is that the CHT's and oiltemps have been like this since break-in in 2008 and up until last Fall. Then SOMETHING must have happened resulting in lower oil-temps.

I wish I knew where to look next.... so I can find the reason why the oiltemps has become so low all of a sudden....

Any ideas anyone?
 
You must log in or register to reply here.
Back
Top