oil temperature

Hi Joe,

Oil temp 65C is far too low - check out the Rotax Operators Manual for your engine.

The "milky film" on the inside of the cap is likly an oil/water emulsion.  Its presence suggests that the oil has not reached a high enough temperature to completely drive off water in the system.

My suggestion is;

Block 1/3 of the coolant & oil radiator - go fly. 

Record temperatures for Climb Out (CO) and Cruise.

Land

Either add to or subtract from blocking material, depending on engine coolant/oil temps in above test.

Go Fly

Repeat as many times as needed to fine tune blocking.

Ideally your CO temperature should get over 100 C for an extended period, to drive off water/volatile fractions in the oil/crankcase.

From poor memory, Rotax allow  a peak of 130 C for both oil & coolant. Prefered temperatures are mid 90 C to 10 5C .

NOTE: Be sure to record the ambient temperature -  lower/higher temperatures will effect the engine temperatures accordingly.

HI Joe

What Sean said....check your operators manual.  

The milky film is emulsified water in your oil from condensation not getting hot enough to boil off.  You need to hit at least 90 C to just over 100C, (100C is boiling point of water) for at least 5 mins of each flight.  I like to see oil and water in the same range so that keeps the engine nice and clean.  If your coolant is too cold it allows the water to cause emulsion in the oil tank and that is then passed into the engine.  (not a good idea) 

Cheers

Thanks for the advice.  I only have oil temp, CHT and EGT; no coolant temperature sensor., but I guess CHT is a proxy for coolant, as only the heads get coolant(?). Can’t figure out a way to do this safely; too much tape could cause overheating.  Also, as temperatures change, so too would the amount of airflow restriction.  Kind of wish I had cowl flaps…

I guess I have an aircraft that needs to stay grounded when it’s cold (below freezing).  

It still blows my mind that Rotax doesn't provide thermostats. Crazy that we have to resort to taping radiators and oil coolers on these modern engines. 

Joseph Ricciardi wrote:

Thanks for the advice.  I only have oil temp, CHT and EGT; no coolant temperature sensor., but I guess CHT is a proxy for coolant, as only the heads get coolant(?). Can’t figure out a way to do this safely; too much tape could cause overheating.  Also, as temperatures change, so too would the amount of airflow restriction.  Kind of wish I had cowl flaps…

I guess I have an aircraft that needs to stay grounded when it’s cold (below freezing).  

Joseph

The 9 series measures coolant temp since 2014 with the change they did moving the temp sender from a dry hole located on the lower side of the cylinder head to a sensor at the top that is into a wet chamber of coolant.  Both ways the heat is a direct reflection of the coolant.  Given there is only liquid in the heads the engine has no lower limit, only an upper limit.  (shock cooling is the problem when you have liquid cooled cylinders but not just heads) Yes it works better with the head at the upper limit but runs with even cold fluid.  

The design of the aircraft determines the radiator size and mounting.  The design airflow is also something that has to be verified from each aircraft design and that also can vary from region to region.  In one case flying in hot arid conditions to damp cold regions.  Like any aircraft design it is up to the OEM, or builder, to provide the testing and balance of radiator, airflow and such, to get the engine into the right range called out in the installation manual.  Cowl flaps, or winterizing kits, are commonplace in general aviation.  Again this is normally done by the OEM in design.  

My preference is no tape, that generally robs cooling air from other parts that may need it.  The same problem can occur when using cowl flaps.  If this cooling issue, too cold, is constant that suggests the radiator is too large or the airflow is not correct for the location of the radiator.  I would work with your OEM to see if they have a solution first. 

Cheers