High Oil Temps - Pipistrel Virus SW

Since my last post I have been doing more investigation and have conducted several flight and have found a consistent behavior in the oil temps.

2016 Virus SW - Experimental
912 ULS (100hp) ~ 100 hours
MT Prop.
Cowling Style shown in picture

Here is a description of the flight profile I encounter when I fly the airplane. 

1. Solo flight - OAT ~85F, 1300' MSLfield elevation, (although I have flown this profile on warmer days and cooler day; it doesn't seem to matter much.)

2. Warmup / Taxi / runup ... letting the oil warm up prior to takeoff

3. Takeoff - Full power / prop forward

4. After takeoff - Full Power / Prop back to 5500

5. Climb to 4500' MSL, 26" Manifold Pressure / 5500 RPM @ 85 KIAS (approx 700fpm climb), oil temps steadily rising into the yellow

6. Level off and establish steady state cruise. 25" MP / 5200 RPM, -5 degrees flaps, 115 KIAS, oil temps still rise higher into the yellow.  I fly level for several minutes and watch the oil temps continue to rise.

7. Power descent, 25" MP / 5200 RPM, -5 degrees flaps, 135 KIAS, oil temps still rise higher into the yellow.  At this point I throttle back to keep the oil temps out of the red.

8. Landing and taxi back - Oil temps falling, but often still in the yellow after a short taxi from the runway to my hangar.


So that's the basic repeatable flight profile.  Regarding coolant temps...During climb, coolant temperature rise into the yellow, but nothing alarming.  During cruise, the coolant temps are down where they should be around 220F.  During a power descent the coolant temps go down to around 215F.



Areas I've investigated:

1. Oil System / Lines are routed correctly per Pipistrel, I made every effort to keep oil lines as far from exhaust as space permits
2. Correct oil cooler installed
3. No sharp bends in oil lines, no sharp bends that would collapse the oil lines when they are warm.
4. I verified the function of the oil thermostat, however I have since removed it from the system to ensure that 100% of the oil goes through the oil cooler and take that variable our of the troubleshooting.
5. Cowling inlet is well sealed against the oil cooler baffling.
6. Oil cooling baffling is well sealed against the oil cooler.
7. Correct oil and qty (Aeroshell Sport Plus 4)
8. Tried changing the oil filter in case of blockage
9. Checked oil cooler for blockage.
10. Installed exhaust wrap tape onto the #2 exhaust near the oil filter / back of oil cooler and also near the #3 exhaust where the oil line returns to the oil tank.
11. Swapped Coolant probe lead with oil temperature to ensure this isn't an instrumentation error.
12. Ensured that I have the correct sensor type selected on the Dynon.
13. Verified temp versus instrument reading using an infrared thermometer.

Lastly, I've been in touch with three Pipistrel Dealers, two of which operate regularly in warm climates.  They have told me that high oil temps are usually not a problem on the carb equipped Rotax 912 ULS Virus SW and that not getting the oil temps high enough is usually the issue on the Rotax 912 ULS Virus SW.  BTW, I'm in Northern California away from the fires.  It's hot here too, but I've been doing these test flights in the early morning before it gets too stinking hot.

Based off the data I have collected, I am suspecting that this isn't a problem with the engine oil system or cooler, but is an issue with the airflow through the cooler.  The fact that level off, power descent, and higher airspeeds does nothing to help cool the oil is leading me in this direction.

Please share your thoughts on this. I'm desperate to get this fixed already.

Thanks,
Glenn Gordon

Reports from the field suggest that it is actually the coolant temps  that are the culprit.

If you get that under control, the oil temps will follow hand-in-hand.

One factor: Pipistrel puts the coolant rad on top of the engine and modifies the coolant expansion tank by cutting off the “red-cap” neck and welding on a bleed port. This port uses an aluminum bolt to seal it and if you want to bleed the air the bolt is miserable to remove as the aluminum on aluminum threads bind together. Plus, you have coolant pouring out as you try to get this bolt back in place.

As the coolant heat cycles, air is trapped in this expansion tank and this contributes to the loss of cooling capacity.

One possibility: the expansion tank could have the top completely cut off and a concave top welded on, so air cannot be trapped, just like the optional tank Rotax has for this radiator configuration: item #13 in the attached picture. Unfortunately, this tank is not available for the 912iS so Pipistrel would have to change their modification of the existing tank to replicate this style. You could perhaps have it done at a local machine shop that specializes in aluminum fabrication...

Rotax-Owner could be correct, your coolant temps are about 20 degC higher than mine and I know from personal experience that if your coolant temperature is high then so is your oil temperature. I find that my oil temperature is about 20 degC hotter than my coolant temperature. If I block off part of my coolant radiator in the winter then this also helps keep the oil temperature up, otherwise it can be quite difficult to warm up the engine and get the oil to 100 degC to burn off the moisture.

Hi Garrett, we have the same issue in summer in South Africa in our 2012 Virus SW. Please could you send  or post some pics of the cooler you used as well as the position that it is fitted.

Thanks Paul