Oil Cooler Air Theft Does Affect CHT

[David-aviator]

#4 CHT has always been 15-20F hotter than 1-2-3. Yesterday, with the OAT at 55, the air flow to the oil cooler was closed and after 5 minutes #4
CHT was the same as #1, 15-20F cooler.

So if balancing CHT's is on your agenda, do not overlook the affect of air going through the oil cooler, that stolen air is not cooling the cylinder.

My cooler is remote with a 4" SCAT tube providing air from the aft baffle at #4 with a butter fly shut off valve. The installation idea came from the RV-10 as I was obsessed with having adequate cooling after several years doing battle with cooling issues and the Subby H6.

For those thinking about departing from the standard Van's oil cooler arrangement, good friend Roger Mell is working on baffle install and it was determined yesterday a remote mount on his -7 won't work as it does with my -7A due to the engine mount differences. We also discovered the double pass SW 8432R cooler will not fit the aft baffle, the cooler is 1" too wide. So he arranged a swap for the 8406 which is the same size as the Van's cooler, which probably is a Niagra.

This not to suggest the standard Van's set up is less than necessary, there are plenty of guys flying with it and all is well. But there also are some who are at war with the issue. I decided to go with SW because they are hands down a better cooler. Yea, they cost more but this is one case where you get what you pay for. The Subby H6 had Niagra's and that may have been half the cooling problem. With the Lycoming, I am pleased to say there are no oil cooling issues at all. If anything, it runs too cool.

(Very nice day to fly yesterday morning with still air. But it looks like all that will change in the next 24 hours with a cut off low approaching from California.)

[cjensen]

I have split CHT's that I'm trying to figure out too...but mine are opposite of yours. I have 1 & 3 higher than 2 & 4, and the oil cooler is baffle mounted off of 4. My right side CHT's are 50-60 (80-90 in a climb) hotter than left side temps...now, I am carb'd, so that in itself is probably the answer, but it's still odd to me.

[jdeas]

I purchased the remote oil cooler kit last week from Spruce. It appears to be a 3" instead of 4" tube. Has anyone that used this kit had troubles with enough cooling in a 7 (not 7a) setup?
Anyone moved the attach point from behind #4 to somewhere closer to the center line of the engine to balance the cooling a bit better across the cylinders?

[49clipper]

Dave,
I could have saved you some time on that subject. Over the years I have found the oil cooler air does indeed affect #4. I finally reduced the 3" inlet to 1.625" and found that to be perfect for oil cooling and #4 cooling. Under 60f I closed it completely. My number four does run hotter but now its mixture distribution as the cause. That 3" hose is not needed at all.
Jim
RV-6
Aero Estated

[rvbuilder2002]

Originally Posted by 49clipper

Dave,
That 3" hose is not needed at all.
Jim
RV-6
Aero Estated

I strongly disagree with a generalized statement like this.
I do not at all dispute whether it works fine with your engine, but I have learned over the years that not all engines are the same.

I have removed engines for overhaul and after reinstalling with the exact same baffling and cooler set-up, seen oil temps and CHT's that were 15 degrees different after break in, than they were for the life of the engine before overhaul.
It is always best to start off with an installation that you know will cool well enough (particularly for the critical break-in period) and then modify to meet the needs of your engine later.

[David-aviator]

Originally Posted by cjensen

I have split CHT's that I'm trying to figure out too...but mine are opposite of yours. I have 1 & 3 higher than 2 & 4, and the oil cooler is baffle mounted off of 4. My right side CHT's are 50-60 (80-90 in a climb) hotter than left side temps...now, I am carb'd, so that in itself is probably the answer, but it's still odd to me.

Chad,

Make sure the cylinder numbers correspond with what you are seeing on the panel. Grand Rapids recommends seeing the top left number as #1, the left front cylinder. That would mean #1 indicator was actually Lycoming #2 cylinder, viewing from the aft end.

I had to disconnect a probe a while ago to confirm how it was hooked up, I had forgotten how I did it. My #1 indication is the Lycoming #1 cylinder, right front cylinder, viewing from the aft end.

[cjensen]

Yeah, I thought of that too, and double checked everything pretty early on...I have the EFIS set up to match the Lycoming numbers.

[TX7A]

David,
I have a setup similar to yours. My cooler is an SW8406R on the F/W, 4" scat to usual #4 baffle location. ECi O-360 C/S w/oil squirters. Not flying yet.
I'm getting concerned about the very problem you have described...too much air being directed to the oil cooler and not enough to #4. I'm going to make a go of it with what I have and see what happens with temps. If #4 gets too hot, I could experiment with partially blocking the 4" opening. But, not something I would really want to do.

For future reference, do you know the OAL of the butterfly valve? I'm not sure I have room to squeeze it in behind the baffle & still have room for the scat.

Thanks.

[David-aviator]

Originally Posted by TX7A

David,
I have a setup similar to yours. My cooler is an SW8406R on the F/W, 4" scat to usual #4 baffle location. ECi O-360 C/S w/oil squirters. Not flying yet.
I'm getting concerned about the very problem you have described...too much air being directed to the oil cooler and not enough to #4. I'm going to make a go of it with what I have and see what happens with temps. If #4 gets too hot, I could experiment with partially blocking the 4" opening. But, not something I would really want to do.

For future reference, do you know the OAL of the butterfly valve? I'm not sure I have room to squeeze it in behind the baffle & still have room for the scat.

Thanks.

Sam,

My cooler is the 8432, a double pass unit and 1" wider than yours. Your cooler is single pass and should be OK.

The cooler does affect CHT but not by much, maybe 20F.

You can check out the SCAT valve here

http://www.nonstopaviation.com/index.php.

[TX7A]

Okay, thanks.
It looks to be about 5" on the length for a 4" valve.