Oil tank breather

The Sportplus 4 has the needed gearbox additives and can deal with the lead if you need use 100LL.

This is an interesting thread. I had a 700 hour 912UL that suffered a valve failure and required a rebuild. Part of that rebuild involved replacing the piston rings along with a few other internal parts and the oil pump was re-shimmed. Before the rebuild I was buring about 60ml of oil per hour. After the rebuild, this doubled to about 120ml/hr. I also had high oil temperatures.

After trying to run in the new rings for nearly 100 hours I had to give up and sent the engine away to be looked at again. Nothing wrong was detected after a complete strip down. I reinstalled it and had the same problem again. After trying various things to resolve it I eventually bought another engine! That fixed the oil consumption problem but I still seem to have an oil temperature that is slightly too high.

I changed the temperature sensor, swapped the gauge, changed the oil hoses and the problem still remains. I've even taken to removing the coolant radiator and run hot water through it whilst observing it with a thermal imaging camera. The hot water flowed evenly through the tubes and so there doesn't appear to be a blockage there. I plan to do the same with the oil cooler when I can get down to the plane next.

I would love to solve the oil consumption problem in my previous engine (which I still have) and the high oil temperature which has afflicted both engines.

I doubled the size of my oil cooler and added a Thermostasis oil thermostat oil temp always 210deg F after the cooler, winter and summer including fast warm up times.

https://www.aircraftspruce.com/catalog/eppages/xcomthermostat.php

On the oil consumption was a diamond hone used for the new rings so that the rings seat?

I don't think that the cylinders were honed. The original honing marks were visible in the cylinders but that is no guarantee of anything. Do you have any experience of honing Rotax cylinders and how long it takes to wear in a new set of rings?

The regulatory environment in the UK does not allow you to fit a larger oil cooler. The standard cooler used to be OK and there are another 150 Eurostars in the UK that do not require a larger one so something has changed in my set-up.

I learned of the diamond hone in the Rotax Heavy maintenance class the cylinder wall has a ceramic lining diamond is the only thing that can touch it. It has been pointed out on this forum that high temp combustion gas/excessive blowby past the rings can dump alot of heat into the oil. This blowby from unseated rings may be the cause of your high oil temps.