Low oil temperature post operation of about 02 hours

Nicolas B wrote:

I have a similar behavior with my 912S3: it increases gradually up to around 78°C, then stabilizes there whether the OAT is 0°C or +30°C. On warm days during climbout, it can go up to 85/90°C, then it goes back down to 78°C during cruise.

 

After asking the aircraft manufacturer about this, I was told the oil thermostats were working as designed and stabilizing the temperature around 80°C, well above the minimum temp.

 

 

 So does your aircraft actually have an oil thermostat?  Many do not- it's a bit uncommon to have an oil thermostat retrofitted to Rotax engines.

Reid,

  do not fall into the trap of thinking that what happens in your small part of the world is the "common" and what happens elsewhere is "uncommon". In my small part of the world thermostats are not uncommon both from the factory and retrofitted.

I suspect that both Nicolas and the Manufacturer of Nicolas's aircraft know that particular aircraft better than you do ?

Dear Glen,

I am very intrigued by your response because I have been trying to get my 912UL oil temperature up to the Rotax spec and it seems very odd to me that the main "fix" we hear is to "cover the oil radiator with tape". For a tech outfit like Rotax to expect us to do such a low tech thing concerns me.

Then I read your assertion:

"The theory that you need to get to 100 deg C is of course BS. The explanation that you need to get that hot to drive off any moisture in the oil is based on not understanding the physics of water vapour and partial pressures. Any oil temperature above ambient the water vapour will start to leave the oil. The hotter the faster this happens. 80 degrees c will be fine."

What you say makes sense from common experience. Water evaporates into the atmosphere all the time at temps much lower than 212º F. On the other hand, the pressure inside the oil system may not allow the moisture to evaporate out of the oil until it gets to the higher temperatures Rotax calls for.

You are saying 176ºF (80ºC) is OK and I am assuming you mean that is the highest temp attained during a flight. Can you provide more to go on. It sounds like one of those "common sense" assertions that ends up being wrong because it doesn't account for other unknown issues.

Thanks.

PS: It would be mighty cool if a real, Rotax engineer would clear this up. Are any of you listening???

I am not an engineer, just been maintaining my Rotax for 10 years and I would say this, if you have any sign of water on the oil tank cap after a flight the oil temp is too low.

On my aircraft I had high summer oil temps with the stock small cooler so I installed the large cooler in conjunction with the Thermostasis oil thermostat and both winter and summer the oil temps are perfect about 200 deg F average after the cooler and never less than 190 deg F with a very fast warm up time. 

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

On an aircraft with an Oil Cooler and No Thermostat, The oil passes through the oil cooler and the amount of cooling is determined by the Ambient Air temperature, The size of the cooler, and the amount of airflow.

More flow, larger cooler, and lower temp produce more cooling. (Lower Temps)

The easiest way to produce LESS Cooling (Higher Temps) is to reduce the virtual Cooler size by blocking the airflow to the cooler.

The Taping of half of the cooler is equal to replacing the cooler with one half the size, only a lot easier, quicker, and cheaper.

The more expensive options for less cooling are to reduce the airflow with mechanical air flaps or reduce the cooling oil flow with an oil bypass thermostat.

The bypass thermostat might bypass the cooler until 190°F is reached allowing the engine to heat up quickly, but after that, the temperature control reverts to the same conditions that exist if you had no thermostat.

The thermostat controls the heating of the Oil UP to 190° and Not the Cooling DOWN to 190°. 

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The oil in the Oil Tank is openly Vented to the atmosphere and then vacuum sucked back into the Oil pump.

There is no appreciable "Pressure" in the Oil System other than within the limited confines of the Oil galleries of the engine.

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You will not find any "Real Rotax Engineers" on this site.

This is an Owners/Users group composed of a bunch of very intelligent and experienced individuals, none of whom are employed or vetted by BRP/Rotax corporate.

We may not speak the official policy of the corporation but that doesn't mean we don't know what we are doing.

Having said that, and in all seriousness, you are well-advised to form your own opinion as to whether the information presented here is accurate or just a bunch of exhaust smoke!