Coolant Temperature Measuring/ 912

My thanks to Des & Roger - I had missed the Rotax Installation manual suggested location, for the "coolant exit temperature" sensor .

I guessed that the "coolant exit temperature"  measurement was likely to be of no additional benefit to the pilot but as Rotax went to the trouble of referring to it, I thought I would ask.

On a related topic:

I have just completely redesigned/fit of the cooling system on my aircraft - all temperatures are now well within Rotax recommendations & my comfort zone.

Oil Temps: Ground about 50/70C - Climb Out 105C - Cruise 97C

Coolant Temps: Ground 70C - Air 85C

Ambient: Ground 32C - 6500 ft 22C

My question: In Cruise, is there any down side/negative, to having a 12C difference, between oil temp and coolant temp?

Hi Sean, 12C is, in my opinion, not worth mentioning. Don‘t bother, keeping the perfect temp setup in mind that you achieved.

I happen to know suppliers of heat exchangers that combine oil and coolant cooling and suggest that it is somewhat desireable to have exactly identical temps for oil and coolant. I am convinced that is rather marketing talk than a real factor. 

The positive results from your redesign force me to pose the question if you made any radical changes to achieve you recent temp framework. I‘d be very interested to read about it.

Hi All

There are design limits for several reasons.  First oil must attain over the boiling point of water at some point in flight.  Generally this will be in WOT for climb or some other area of flight where you generate the most heat.  Naturally we don't want it to exceed the temperature limit.    This is very important to remove moisture from the oil that can accumulate and emulsify in the oil.  Sean getting 105C on climb is a good example to vaporise the water out of the mix. 

The coolant temp is a bit more difficult to explain.  For the most part many people actually run the coolant far too cold.  We need to keep the cylinder heads near the temperature of 100 rather than 75C when in cruise flight.  As long as we are not excessive on the WOT in climb.  This is important to get the best combustion in the cylinder head.  If you use AVGAS with lead this is extremely important to purge lead buildup in the heads and valves.  Running too cold will accumulate excessive deposits and you will be not getting a good burn.  

Just my opinions but do some research on liquid cooled engines and this is a common thread. 

Cheers

Thanks RW

Usually its much easier to raise, than lower, the temperature in one or both systems, so I think I will have a crack at trying to bring my coolant temperature closer to the oil (mid to high 90C's). I don't want to compromise my general airflow (might cause the oil temps to go higher) so will start by placing a small strip of adhesive aluminium tap over a section of the Radiator and see what happens.