High Oil Temp 912ULS

250F is pretty high for cruise and for an RV-12 in cruise.  85F isn't that hot. Some may see that on a hot day in climb, but you shouldn't in cruise. I'd try to find the issue and see if you can at least drop it 10F and maybe 15F. Flight Design CT has the coolant radiator and then piggy backed on that is the oil cooler and right behind that is the muffler.

Roger - Thank you for quick reply....

James - Most if not all light aircraft engine gauges are at best indicators. That is, as long as they remain fairly consistent in their readings, all is usually well.

The pilot should monitor for any change, not so much for the numbers.

If your oil pressure remains acceptable, then it is likely your temperature gauge is reading high (ie above actual temperature).

Sean Griffin wrote:

James - Most if not all light aircraft engine gauges are at best indicators. That is, as long as they remain fairly consistent in their readings, all is usually well.

The pilot should monitor for any change, not so much for the numbers.

If your oil pressure remains acceptable, then it is likely your temperature gauge is reading high (ie above actual temperature).

Sean - What you say is true, however my real problem is that I installed a new exhaust system and oil temps are now 30F higher on hot days.  I have Dynon D180 EMS and I think indicated temps are pretty close to actual.  

My real concern is if 250F is acceptable operating temp for Rotax 912 using Mobil 4T 10W40 Full Synthetic Oil.  I have been searching internet (I know – not good idea) and see that full synthetic oils can operate near 300F.  I spoke with tech support at Mobil and they said they don’t publish a max operating temp, only that their product is good for high-revving motorcycles and high temperatures.  Tech support said they would investigate and get back to me in a few days.  Hopefully they will, but could be ploy like telling kids “later for sure…”

If this didn't happen before the new exhaust system you need to find out what changed to correct it. Was it a stock RV12 system or an aftermarket?