Hello everyone!

I'm currently in Phase 1 with my 701 and working some kinks out. I love the engine, but I'm battling higher-than-normal oil temperatures. I'm at sea level (40') cruising at 2400 rpms on a 90-degree humid day. My temps keep bumping 238 degrees. I have ensured that all gaps around my oil cooler have been sealed to allow the most air to go through the coil and I know the temperature is accurate. 

My CHT's are great, oil pressure only drops when the oil gets hot. My air filter is on top of the engine and hasn't been relocated, but has a naca scoop to it.  

Has anyone run into this issue? Thanks!

PS. Before anyone points out that my cooler isn't centered in the hole....I know. However, no part of the cooler is covered and it has to be installed this way to miss the oil thermostat housing. 

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It has always bothered me to see the oil lines entering and exiting from the bottom of the cooler but AFAIK that's pretty standard for UL Power engines.  I assume the cooler must be designed to prevent an air bubble at the top of the cooler that could partially block oil flow?



There is a thread on this forum about oil coolers and oil temperature issues with the 350i model. I fly the 350i in a Cruzer and changed to a larger, more robust, oil cooler. I had temps in the 120 range. I only attempted to fly on a 90 degree day once with oil temps climbing into the 120 degree range before I decided hot days are not for flying Zeniths. The larger cooler has made a big difference. My oil temp now runs in the 195-210 degree range. In cruise it runs under 200 degrees.

Another resource is Ray Lawerance at UL Power. Ray talked me into changing oil coolers, he does hands on work on airplane engines. 

238 degree oil temps, as you know, are to high. If you want to learn more about the impact of temperatures on conventional and synthetic oils you may consider reading articles on the site listed below. Bob does a good job of discussing all about motor oil.


If you want to talk about changing oil coolers feel free to contact me. Be forewarned, my oil cooler mounts do not use rubber dampeners:)


208 680-2561

Hello Chris. I have the same power plant and cowl system. I haven't had any oil temp issues. Though, I think my oil cooler is smaller in height but the same width. I might be a double row, though. Cant tell by the pictures. I will trade you ideas on it for help with  #2&4 cylinder baffles design you use to keep good cht's. I did mount the rubber sock to the oil cooler itself... and the mis align is just the way it worked out. But seems fine.

I recall a service bulletin for changing the oil cooler temp spring (inside the oil filter adapter). . I did it in mine before starting it. Mine runs a constant 200. 


My baffle setup was straight forward. I attached a couple of photos. 


What did you do about the misalignment for the upper cowl air inlet to the baffles?


I’m wondering if a fan would help? 

A fan would probably be too much electrical draw and not enough air,  it could become a block if air is trying to get past it faster than the fan could go. Does your opening in the cowl cover 100% of the cooler or is it choked down? 

It still covers 100% even though it is offset. Do you have a picture of the bottom of the cowl? I spoke with Ray and we are both scratching our heads. The only thing I can think of is that there isn't enough of an opening for the air to escape. 

Attached you will see a photo looking into the baffles. It looks a bit different than yours. 


Should be plenty of space for exhaust of air. An air bubble but, seems less likely, oil type? Is it possible the cooler is flexing away from the opening in flight? I have a similar mounting but the braided lines make up for it adding rigidness to it. And you completed the change out of the thermostat spring? 

Thanks for the photos. I will modify my inlet air and see if it makes the temps balanced. 

Here are some basic photos. Looking for the best ones still.


Did you ever find a solution to your heat problem? 

Hi Chris, last year I help a friend with his 601HDS after he switched from an 80hp rotax to a 100hp.  The installation was done by his A&P friend.  He placed a 5 x 10 inch oil cooler attached to the engine mount feed by a large NACA duct for cooling air.  His oil temps were very high.  240-250 degrees(surprisingly, Rotax says 240 degrees is ok??) so we tried adding a bunch of things to bring down the temp but the only thing that help, (very little) a large scoop on the side of the cowling at the rear of the NACA duct(temps were 230).  So we added two 12v DC fans to the back of the oil cooler and that brought his temps down to 180-200 degrees.  I don't remember the amp draw but it wasn't that much.

On a side note, I googled what is the oil temp of cars we drive.  The answer was 230 to 260 degrees. 



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