Thread: Oil temperature

Using the 100 hp Rotax engine, on the CT, my oil temperature never exceeds 75˚ to 80˚(Cels), while the Rotax Manual recommendation mentions 110˚ in accordance with the manual.
Up to my knowledge there is a oil thermostate available, but its not certified by Rotax!
The question arises what to to, as a friend of mine had a engine stop after 800 h and the reason given by Rotax, was flying with not enough oil temp. which leads to additional wear and tear and therefore to a total overhaul of the engine with a cost of € 12.000.-
After it was proven by the certified maintenance shop, that all maintenance was done in the correct manner, Rotax was able to give a "discount" of € 4.000.- which still leaves € 8000.- for the repair of engine due to "cold engine oil"
As we have here in Germany not such extreme climate as in part of the US, the question is, if there are other recommendations how to increase the oil temperature, besides using tape on the cooling system. If that is the only way - then do I have to use that all year long??

This is a special task for our Rotax specialists and I appreciate any advise in this matter.

Best regards

Roland

Roland,
I’m glad you are happy still having as many takeoffs as you have landings. As for myself, I am happiest during the periods when my takeoffs exceed my landings by one.
I am no Rotax expert but I think I can help with your low temperature problem.
Water collects in the engine oil both as a product of combustion during operation and due to condensation from the atmosphere when the engine is not operating. Water compromises the oil’s lubricity and causes corrosion. It is desirable to boil this water out of the oil regularly. To do this the oil has to reach 100 C (212 F) at sea level. 90 C (194 F) will work at 3000 meters (10,000 feet) where the ambient pressure is lower and consequently water boils at a lower temperature.
If you are not reaching these temperatures at least once during each flight you are likely to accumulate water in the oil which will eventually cause damage.
Although a thermostat would solve this problem by restricting the flow of oil to the oil cooler until the oil gets hot, a thermostat reduces the aircraft’s reliability by introducing a single point failure; if it sticks in the closed position you engine is toast. Thermostats also add weight, cost and complexity to the aircraft.
An alternative is to block some of the airflow to the engine. Some aircraft use pilot-actuated cowl flaps for this purpose. Flight Design doesn’t offer this option. Indeed, their goal is an aircraft which is insensitive to pilot error. As soon as you add a cowl flap, someone will forget to open or close it.
A simple alternative is to tape over a portion of the radiator prior to flights in cold conditions. This blocks some of the airflow through the radiator (which cools the water) and the oil cooler mounted directly behind it.
We apply a 2-inch (about 5 cm) wide strip of an aluminum-backed tape vertically down the middle of the radiator during the winter. This keeps our oil temperature up in the operating range without overheating. During the spring, when we see higher oil temperatures we remove the tape.
I like the aluminum-back tape because it stays on and doesn’t leave a sticky residue when we remove it. Other tapes might work as well.
You might give this a try, adjusting the width of tape to meet your needs… and always monitoring oil and water (head) temperatures carefully during flight.
Mike Koerner

Hi Mike,
first of all thanks a lot for your quick advice!
You are right, that obviously the only prevention is to use the Tape. I also don't want to run into a warranty problem by using a not certified thermostat. Also here in Germany we have to consider each additional weight as we use the CT as "Ultralight" with a MTOW of 472,5 kg We are already on the heavy side considering an empty weight of 330 kg You are lucky with your 600 kg where you don't have to make the choice between a passenger or a few Gal. more of fuel

Thanks again and happy landings
Roland