High oil temperature on 912 iS

Vlad,

A few things. 

Assuming your engine is an 912iS "Sport", you are correct that peak torque is at 5000 RPM per the performance data in the Operating Manual.  With the non-sport 912iS (older engines), the peak torque is very close to max continuous power at 5500 RPM. I have the 912iS Sport in a Bristell, and the engine feels best cruising at 5200 RPM, which is actually just past peak torque. My prop is adjusted for 5050 RPM on the takeoff roll, which will give me a max WOT RPM right around 5590 RPM at 4500' in level flight.  I have tried many settings and this is what I think the 912iS Sport likes best.  The other good thing about this setting (for the Sport engine) is that you are right at peak torque during takeoff, and you are getting most of the HP. 

I have a 2016 model, which has the oil radiator mounted up front with and oval shaped air inlet much like your Belmont.  On a 19C day, my oil temp will reach 114C on a sustained full power climb at 82 kts, and in level flight that settle down to about 103C. A hotter day I might see 116C on climb, which is where I have my caution indication set up.

I believe some of the earlier 912iS Bristell (prior to 2019), did have higher oil temps as you describe.  I don't know why some did and some did not, but it may have been different propeller configurations and settings. My plane has a Duc Flash, which has a fairly small profile down at the root, whereas the prop on your plane is wider in that area and may disturb the airflow entering the oil radiator opening in the cowl.  I agree with Roger and Rotax Wizard that your plane would run cooler with a less aggressive propeller pitch, you should be able to exceed 5500 RPM in level flight somewhere around 4000' in altitude.

In 2019 Bristell changed the radiator for the 912iS Sport powered aircraft from the Rotax "Large" to "Extra Large".  They also improved the cowl with a larger airflow opening that exposed more of the radiator to airflow.  At least one dealer in the USA was offering a similar modification for existing owners of older planes and I know of several that were done. This dropped the max oil temp approximately 10C.  I purchased the Extra Large Rotax radiator with the intent of doing the modification myself, but I only get over 115C on very hot days, so I have never found it necessary. 

The prop adjustment on the 912iS Sport is delicate. Too much pitch (load) and the CHT and oil temps can be high. Too little pitch and you will get cooler CHT and Oil temps, but the EGT will go up towards the max and shorten the life of the exhaust system. The settings I mentioned above seem to strike a good balance. 

Hello Jeff,

I suppose there's a typo in the take off RPM. Can you confirm it's 5500 RPM that you set?

Regarding the propeller, assuming you have the Duc Flashblack-3-R https://www.duc-helices.com/en/3-blade-inconel-flashblack-r-propeller-right-hybrid can you share some performance data that you get in cruise from your Bristell with 912iS Sport?

Thanks.

Vlad
I have a fixed pitch prop that is ground adjustable.

https://www.duc-helices.com/en/3-blade-inconel-flash-propeller-right

Up until a recent rule change variable pitch props were not allowed here in the USA on light sport aircraft.  No, that was not a typo, I have the prop set so it’s reaches 5050 on a standard day on the takeoff roll. If it’s very cool out, I may get 5100.  If you have an in-flight adjustable variable pitch prop, this conversation changes. But back to your oil temp…

It’s interesting that your coolant temp is relatively low, and your exhaust gas temps are quite high.  This would typically indicate the engine is in a somewhat light load condition.  Manifold pressure at 25.8 supports this. The oil radiator and coolant radiator both remove heat from the engine so I would expect both to have a similar trend, and they don’t.  The coolant temp is a better indication of the engine CHT, while oil temp is indicative of the entire engine temp. So CHT is fine. 

While I do support the idea of cursing over 5000 RPM with this engine, nothing about how you are operating the aircraft suggests a cause for your high oil temp.  I think you need to inspect the oil cooling system as Roger suggested earlier.  Look for tight hose bends and examine the airflow and check the oil thermostat if you have one. This could be systemic withe the Belmont, have you contacted them?