HELP----Ul260iS High oil temperatures

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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Permalink Reply by Chris Elliott on May 26, 2023 at 4:13pm

I have addressed everything I can think of. I relocated the oil cooler and lines further away from the oil pan and ensured it was centered and sealed in the inlet. I removed and replaced the baffles with plenums and installed a scoop to the NACA to ensure the most amount of cool outside air goes across the air filter. I’ll be testing it tomorrow, but I’m not confident this has fixed the issue. I think adding a fan or increasing the outlet size will be my next move. 

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Permalink Reply by Chris Elliott on May 26, 2023 at 4:17pm

More pictures.

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Permalink Reply by Larry Koepke on May 29, 2023 at 9:14am

Any luck with reducing temps? Nice looking plenum's and very spacious. Did you fab them?  Oil cooler line extension will add some more capacity, cooler relocation looks good. One of the bonuses of the lines on the bottom was free support. Think it will flex a bit now? 

Permalink Reply by Chris Elliott on May 31, 2023 at 9:51am

Not yet. I can run without the cowling and ALL temps are perfect. It’s a cowling cooling issue. I supported the cooler with some brackets. Talked with Ray this morning and after a bunch of head scratching we decided an additional inline cooler may help. I’m on the gulf coast where heat and humidity rule, and since this is a very slow airframe it might need a little more help. It does me no good to only have good temperatures in cruise. It’s the slow flight where I need them. 

I built the plenums early on, but for some reason went the baffle route. 

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Permalink Reply by Larry Koepke on June 1, 2023 at 9:52pm

So without the cowling all your temperatures are good? How much did they drop from the cowling being installed? Is your oil cooler 100% open to the ram air with the cowling on? Or less than? By the pictures it seems you have a larger cooler than the opening? 

Permalink Reply by Dave Blackburn on August 15, 2023 at 5:32pm

Not an expert, however on my 350 install I remember there was a caution for installing NACA duct for intake air that it could cause too much air behind the baffles (and the oil cooler) causing higher temps.  I saw one of your pics that shows a sizable opening on the NACA.  I’m sure Ray had you dial the thermostat on the oil collar to a lower opening.  I’m east coast Florida with a 350i and Herman definitely had me go with the double stack heavy duty cooler. Flew today at 95 F 65 humidity and saw 205 on climb out and 190 cruise in 750STOL

Permalink Reply by Larry Koepke on August 24, 2023 at 8:44am

What cowl combination do you use? I have a similar issue with that on #4 (290-320) being higher than the rest and 1-3 being well cooler. Oil hits between 200-211, mostly. Thermostat seems to keep it a steady 200 in cruise. 

Permalink Reply by Chris Elliott on January 22, 2024 at 11:57am

I have made a bit of progress. I wrapped my headers and created two additional 2' air inlets and now my temps are still high @230, but not close to redline. I experimented by covering up the two inlet holes and the temperature spiked into the low 240's. 

I'm afraid another oil cooler is in my future. I just do not like the idea of another fail point. 

Permalink Reply by Dean Blood on March 18, 2024 at 3:44pm

Chris, I see Dave made this comment awhile back, but have you tried blocking your NACA duct on top of cowl?

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