High Oil Temperatures

[Tim213]

During my flight testing I have been having an issue with high temperatures. It’s a rebuilt engine from Barrows, so of course it does have to broke in.
However my temps still concern me. The first couple of short flights the CHTs were high, some around 430 and 450 degrees. First I enlarged the cowl exit and the next flight CHTs were better, but my oil temp still very high. I then again open up the cowl exit and completely redid my baffle seals. I also redid the cowl lip. This helped stabilize the CHT temps but again my oil temps were high, starting out okay but just gradually continuing to rise to red line before I would land. Because the opening around my air box was of course covered, it is probably about 2 inches longer in the rear than needed. This limits how much more I can open up the cowl exit. My oil cooler is located on the rear pilot side engine mount. Assuming the oil temp sensor for the Dynon is ok, I’m hitting a snag on what to do next. Thanks for any input.

[svyolo]

I hate to send you down a rabbit hole, because I don't know how drawn cup oil coolers flow oil internally, I tried to find out, including the calling the manufacturer of the one I bought but the rep didn't know either.

If it functions as two manifolds, with tubes parallel between the two, there is a real good chance your oil cooler has a big gulp of air it can't purge. Without changing anything, or buying anything, can you unbolt the oil cooler, invert it so the ports are on top, and run it long enough to get the air out ( vernatherm might have to get warm enough to open, but not sure about that. Another option might be unbolting it, turn it port side up, and physically fill the cooler with oil, then remount it.

If that fixes it short term, you can mount it with the ports up and make up new oil lines.

I read an old thread on VAF where a guy fought high oil temps for a long time, and kept buying bigger oil coolers, with no luck. He finally showed a picture of his install, and the ports were on the bottom. In general, fluid systems are best filled from the top to purge air. The outlet is less important in most cases.

[Ray Strickland]

I agree. Ports should be on top or side, not on the bottom. Also, it looks like your engine mount tube may be restricting airflow exiting the cooler.

[Battson]

Look at these things before you cut any more away from your cowl outlet, in order:

1. Ensure baffle seals are good, look for leaks, and any other place air can sneak around to the bottom side of the engine (spinner, air box, lights, etc)
2. Increase the diameter of the SCAT tube from your baffles to the cooler, at least 4"
3. Round off that sharp corner from the firewall to the tunnel (instructions on this forum)
4. Consider the size and shape of the lip on your cowling, at the cowl outlet
5. Reposition the cooler so there isn't an engine mount tube right behind the cooler outlet
6. Let the cylinders run in a little longer, keep the airspeed and MAP as high as possible (26 or 27"Hg is fine). Keep RPM at or below 2300 (but not below 2100)

[Mark Goldberg]

bafflepics 003.jpg I think the little "plenum" that I have on my four place spreads the air out a little better perhaps than the part you used. To take advantage of the full front face of the oil cooler. For the Model 5 I found a fiberglass part for the RV10 that we are going to adapt that transitions from the baffle right to the oil cooler. Looks like it might help on the Model 5 in a similar way. Mark

[swpilot3]

You might want do check your vernatherm. I had a similar issue with my oil temp and found my vernatherm didn't pass the boiling water test. I replaced it and I've never had a problem with my oil temp since.