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Oil cooler shutter

Scott Hersha

Well Known Member
I thought I would discuss some modifications I made to my oil cooler installation on my RV4, and see if I can get some recommendations or opinions on how to operate my airplane in the winter relative to engine oil temps.

First off, my RV4 has an O-360-A1A, carbureted, one EI/one mag, and a seven row oil cooler. My oil cooler is mounted on the #4 baffle like most RV’s, except there is an angled spacer between the baffle and the cooler (see pics). In the summer, everything is perfect - the hottest oil temperature I’ve seen is 190* during a climb on a very hot day, and then it cooled to my normal 180* +/- after level off. I’ve never seen a CHT of 400 or more.

Now for winter ops. This is my second winter with this airplane, which I didn’t build. The engine runs cool. Last winter I had a blocking plate on the back of my oil cooler, which completely blocked off the back side of the cooler. It helped a little, but only made about a 10* difference. My oil temps struggled to get above 140* on a cold day (Cincinnati). This year, I bought the oil cooler shutter from Alan Nemo at ASA and mounted it to the front side of the cooler. At first it was good. I was able to adjust the shutter (cockpit adjustable) to maintain 180*. However, it was unusually warm. OAT was in the 50’s at my altitude. Last Sunday we had a lunch fly out and it was much colder, although not frigid - about 35* OAT at my low cruising altitude. I flew 30 minutes out and then 30 minutes back, and the warmest I could get my oil temp was 157*, with the oil cooler shutter completely closed the entire way. I ran at 65% power lean of peak. CHT’s were all slightly below 300. Below are some pictures of my installation:

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The last couple of pics is with the shutter open and then closed. I don’t know how my oil temp could be so low with the air completely closed off from flowing through the cooler.
You may be thinking that my oil temperature probe must be bad. Well, me too. So today I removed the oil temperature probe and checked it in a cup of heated water and compared it to two separate digital temperature probes, and all three of them were within 2* of each other, which is close enough for me. These temp comparisons were from a start of about 50* to 195* (the hottest I could attain with my coffee warmer). These temperature measurements kept close pace with each other (the two digital probes, and the EIS/EFIS probe) from start to finish.

It appears that my oil cooler cools the oil just hanging there with no air flowing through it. Restricting oil from flowing through the cooler may help, but maybe not, plus, it adds complexity and possible leak paths that I don’t have now. Should I worry about a max oil temperature of 157* on a relatively cold day?
Maybe I should add a heat muff with the output aimed at the oil cooler? - I’m kidding...... Is there a solution, or do I even need one?
 
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I like that blank off plate as I also suffer from cool oil temps. I currently have my fwd side taped over but I can't cover it all with the tape. I have been monitoring a small crack at my oil cooler baffle corner flange. it hasn't grown in the past 100 hrs so I am hesitant to add any more weight to the oil cooler or even add a shutter. this is the original old style baffle kit without any modification except adding the gusset tube. the crack creates some added flexibility at this flange so it makes me wonder if rubber isolation washers under one side of the oiler cooler would be beneficial to let it float. I'm hoping to get this baffle to 2000 hrs.

I will be continuing to use these cowl inlet air dams in cold conditions to bring engine temps up. this center air dam location allows for even CHT temps. 5 minutes to install. the weight is almost nothing since that are virtually hollow, like a balloon. tuned to be clear of any propeller driving frequencies for both 2 and 3 bladed props.

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I have a o320 in a 9a and block off the back in addition to the shutter in the front. It works ok and allows you to still control the heat with the shutter.
 
Oil cooler air flow gate

O-320 RV-4 with a flow gate on the aft side of the cooler. Airflow taken off of the left rear shroud. The cooler is attached to the engine mount with a steel hanger I designed. There is a plug I put in the round intake on the front, from the engine shroud, that blocks about 50% of that flow when temperatures get below 40. Easy to control air flow. Never had oil cooler temperature problems with this setup. Sorry I don't have more pictures at this time. I'll look for more.......there is some holiday coming up or something.........:)
 

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Scott, FWIW

I have an 0320 Rv3 in Indiana. Oil cooler is completely blocked off in winter with Oil temp around 160-170F. CHT’s are about 295F. Has anyone substantiated that this is a problem ?

OK, pistons are not as large as 350F. H2o leaves oil at 120F. What am I missing ?
PS, where do you fly from.? I would like to come down and see your 4 as I am finishing mine this winter. 😊
 
Steve,
Guess I should put that block off plate back on the aft side of the cooler to see if that helps. I didn’t think it would do anything, since nothing can come through the front side with the shutter completely closed. I’ll try it to see. Do you think your air dams on the inlets could help me warm things up a bit (including oil temps)?
Man - I’m getting so good at removing my top cowl. I think I could do it on a pit stop at Indy!
 
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testing last Winter

it took me all last Winter to get to this air dam design so I didn't get back to back data with and without because it was warming but I concluded they were beneficial for raising CHT and oil temps. I estimated around +15 to 20F degrees. it should not be hard to get some good data this Winter. I put them in when it's below freezing and it warms up nicely and the CHT are relatively even. that was the goal last Winter, to find an air dam that would give even CHTs. placing the post directly in the middle of the cowl inlet was the solution because I had poor results with uneven CHTs if the air dam was not in the middle. so far I have 20 flight hours experience with no adverse findings with the air dams and I will continue to gain hours this Winter.

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Perhaps restricting the air coming out of the cowling would help. I’ve got two plates that attach via Adel clamps to the bottom of the engine Mount on either side of the exhaust in the winter effectively reducing the exit area.
 
Perhaps restricting the air coming out of the cowling would help. I’ve got two plates that attach via Adel clamps to the bottom of the engine Mount on either side of the exhaust in the winter effectively reducing the exit area.

do the CHTs remain even when it's blocked at the exit?
 
Pictures

Hi David, Could you maybe post some pictures?? Or if you're picture challenged, as me, just send some to my email. (I've got the same problem on my 8. Tried the shutter trick. Wouldn't fit. So I've been putting metallic tape on as much of the front of my cooler as I can reach. But if I fly down Florida, now I would have the reverse problem):rolleyes:
 
Hi David, Could you maybe post some pictures?? Or if you're picture challenged, as me, just send some to my email. (I've got the same problem on my 8. Tried the shutter trick. Wouldn't fit. So I've been putting metallic tape on as much of the front of my cooler as I can reach. But if I fly down Florida, now I would have the reverse problem):rolleyes:

I doubt I have any on my phone but will get some from the exit side of the cowling over the weekend if that works.
 
I do not think that once the cooler is blocked off, it is still cooling the oil.
I've owned many planes that had no oil cooler at all and during cold WX ops, the oil would not go above 130F, unless you blocked off some of the air entering the cowl (usually used duct tape)....

On my RV7 summer or winter it is difficult to get LOP CHT's above 310F unless I run an over square power setting. I have adopted 25.5HG over 2350 as a initial power setting and increase RPM as altitude makes manifold pressure drop off.
 
low oil temp

I know we want oil temps to go up to 180 and the minimum is 140 - besides boiling off water, is there another a reason we want the oil to be hot?
 
I know we want oil temps to go up to 180 and the minimum is 140 - besides boiling off water, is there another a reason we want the oil to be hot?

From my (limited) understanding, the viscosity for lubricating all those moving parts is more important than eliminating H2O. And the viscosity is related to the operating temperature.
 
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