Oil cooling

Scott Hersha · #1 07-07-2010, 08:57 PM

This is not exactly a 'new' thread, since there has been countless posts relating to this subject, and I have read them all --- twice. What I need is opinions from those in the know on one of problems relating to oil temps. My situation is not critical, but uncomfortable for me. I have an RV-8 with an ECI Titan O-360, carbed, one electronic ignition, and 9:1 pistons. My cruise oil temp up high with OAT's in the 55-60 degree range are running 200-207. Temps increase in the traffic pattern or during formation flying, with temps reaching 210-217. My baffles are tight - they would hold water if turned upside-down. I've RTV'd every possible opening around my oil cooler (Van's FWF Niagra 2002A). Today I removed my vernatherm and found out that it only touches the seat on about half of the circumference of the tapered valve surface. What I need to know is, does this make that much difference? Even though it doesn't seat all the way around, there can't be that much of a gap in the area not making contact with the seat. How much will that effect oil temperature? I know this oil passing past the seat is not going through the cooler, but how much oil is getting bypassed? And how bad is that? There is a procedure where you can lap the seat up to .010, but then the temp where the vernatherm makes contact and starts cooling through the oil cooler is higher. The alternative is to get another seat - ie. oil filter adapter - and hope this one is seated correctly. I installed and flight tested another new vernatherm today and there was no change.

Another thing I tried after talking to a friend who got this idea from ECI. He said any Van's airplane could get a 20 degree improvement in oil cooling by putting a blocking plate over the #4 cylinder cooling fins where they almost touch the oil cooler on the Van's baffle. Theoretically, the #4 cylinder exhaust valve which is about an inch from the bottom of the oil cooler and experiences temperature approaching 1400 degrees, has a negative effect on oil temps because air passes over this area of the fins and some of it is sucked through the oil cooler. Even though putting a plate in front of this area of the cooler, thereby deflecting the cowl air down through the fins with none going through the oil cooler - effectively blocks about 1/3 of the oil cooler, this is still better than having very hot air going through the oil cooler. Well, I made this modification, and I curved the top of it to 'catch' some air and send it down through the fins to cool the exhaust area of the fins. Net result: zero.... it made absolutely no difference, good or bad. No noticeable difference in #4 CHT or in oil temperature.

My friend Jon Thocker with an almost identical airplane, but a SW8406 cooler is getting 10-15 degree cooler oil. He doesn't have the electronic ignition either. That gives me a higher CHT, because of more complete burning of the gasses in the combustion chamber due to earlier ignition timing, and lower EGT's, because there is less burning going on heading down the exhaust pipe. These numbers are verified in side by side testing with out two airplanes.

What I need is advice on what I can do to lower my oil temps. Obviously, I need to figure out the vernatherm issue first, even if the difference is small. Next, should I get another cooler? The SW8406 is possibly good for 10 degrees or maybe more. The 8432 will give me even more, but I have to remove and modify my rear baffle. I'd like to fix this problem without spending my wife's future windfall if possible. The 8406 is $615.00, and the 8432 is $661.00 at Pacific (both are more at Spruce). I've thought about trying a Mocal/Setrab, but haven't gotten the gumption yet. It would require some engineering and a lot of unknowns - but this is summer and I want to fly.

Suggestions??? I mostly want to know about this vernatherm issue....

THANKS,

elippse · #2 07-08-2010, 10:15 AM

According to the spec sheets for Lycoming 235 and 320, the oil cooler system without Vernatherm has a limiting prssure drop across the oil cooler of 35 psi and with the Vernatherm it's 75 psi, in which case the oil cooler is bypassed. The maximum temp spec for the oil is 245 F, and if you're using semi-synthetic oil, that's not a problem. The engine runs more efficiently with higher temps on the cylinders and oil. I choose to run my CHTs around 375F-395F, and my oil between 100C and 110C, 212F-230F. 210F-217F doesn't seem all that bad to me! It's a choice based on feelings.

fl-mike · #3 07-08-2010, 10:24 AM

Any chance you can borrow Jon's SW cooler for a test? That would help eliminate the cooler and possibly save you some serious $.
Are your CHTs running okay? Your OTs are high, but not excessive (at least from what I've heard) I'd be more concerned about CHT than OT.
How many hours on the engine and what kind of oil are you running?

jabarr · #4 07-08-2010, 10:39 AM

We just fought this on a friends RV8. His temps were OK for a while and started creeping up to the 210-215 range. We did all the normal things like reasealing any suspicious baffle leaks, tried the small baffle at the #4 cylinder etc. We made a spacer that moved the oil cooler aft 3/4" in an attempt to provide a small plenumn at the oil cooler inlet side. When recowling the engine after the spacer mod, we found the seal at the snorkel had torn loose from the airbox. We suspect that this seal defect allowed ram air to pressurize the lower cowl area and disrupted the airflow from the high pressure upper cowl area to the supposedly lower pressure bottom cowl area. The temps are now lower by 10-15 degrees after the snorkle seal repair and the oil cooler spacer. We don't know for sure which change had the most affect but we are happy with the results.

Guy Prevost · #5 07-08-2010, 11:06 AM

I'm sure you've already checked this, but a lot of folks don't seal the ends of the inlet ramps on the upper cowling. The ramps server as nice tunnels to pump cooling air from the pressurized to the non-pressurized section of the cowling. the tighter your baffling is, the better these tubes work to defeat your cooling! Make sure the interior faces of the space between the inlet ramps and the upper cowl are glassed over. Doesn't have to be pretty...

AZtailwind · #6 07-08-2010, 11:34 AM

Not the vernatherm- I replaced the Vernatherm, spring and cleaned up the seat to zero improvement in a citabria that was running a little warm as yours is. Cleaning up the baffle leaks and extending the outlet shroud improved that install. So for me I would not look at the Vernatherm at first. My issue for our RV was to replace the cracked Vans oil cooler- It was too low and too close to the #4 cyl anyway. Being so low on that Cyl is probably what caused the crack from excess Cyl heat. After replaceing with a little larger cooler and raising the mounting as high in the baffle as possible- that was the cure. -FWIW and Your MMV

Bruce · #7 07-08-2010, 05:55 PM

Scott.

I feel the pain. I am in the same situation but my oil temps at
cruise are 225. Hard climb to 6500' and it gets to 235.
I put the 8406 on and it didn't change much. Did you
talk with ECi.
I have the James plenum and cowl.
I will check my snorkle attatch area which could be some
of my problem.
How many hours do you have on your engine?? could that
be some of it.

Everyone keeps telling me to fly as is at 225. Just be careful.

Give me a shout if you need to.
Boomer

Dean Pichon · #8 07-08-2010, 06:52 PM

...it's not the Vernatherm. On a previous plane, I replaced Vernatherm valves multiple times chasing the same (high) oil temp problem. Vernatherms are near useless. Like others have stated, I learned to live with the higher (but acceptable) temperatures. I would suggest focussing on some of the good ideas posted by others.

Good luck,

Dean Pichon

apkp777 · #9 07-08-2010, 07:21 PM

As you probably read on other recent posts, I have struggled with high oil temps, CHT's and EGT's on my ECI -0320. I have seen my temps drop from about 210 to where they are right now at about 195. Everyone say's check the baffles, check the baffles. I did and didn't see any leaks. Here's what I have done so far,

1.Installed doubler strips on the baffles higher to put more pressure on the baffling material.

2.Reduced my oil pressure to 73 psi in cruise.

3.Taped up the inlets with foil tape.

The tape looks really goofy. My wife was not thrilled. She thought the plane was being held together with duct tape. However, it's a sure fire way to block the air from going where you don't want it. I am going to work on the fiber glassing the inlets using the tape as a mold ASAP.

I am running P-mags and my CHT's, oil and EGT's got hotter when I hooked up the manifold pressure line during the climb. EGT's seems to be lower at cruise peak as CHTS are about the same.

Right now I am seeing about 390 CHT in cruise, 1400 EGT and 195-198 oil temp

rvbuilder2002 · #10 07-08-2010, 08:03 PM

Quote:

Originally Posted by Guy Prevost

I'm sure you've already checked this, but a lot of folks don't seal the ends of the inlet ramps on the upper cowling. The ramps server as nice tunnels to pump cooling air from the pressurized to the non-pressurized section of the cowling. the tighter your baffling is, the better these tubes work to defeat your cooling! Make sure the interior faces of the space between the inlet ramps and the upper cowl are glassed over. Doesn't have to be pretty...

This is only necessary if you do not trim your baffle edges to parallel the ramps so that the baffle seal material seals against the ramps on the inboard and outboard sides of the inlet (that is the way it is intended to be). If this is done, there is no flow path through the opening below the ramp.