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:
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?
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:
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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