Oil Temperature

I also wonder this. 

At altitude you don't need 100 c to boil either. 100 boiling point is at sea level pressure.

hi Murray

You are correct however we do not run a sea level pressure system, it is elevated to 1.2 bar above sea level (18PSI) This elevates the boiling point of the coolant.  We also do not use pure water, it is a mixture of chemicals, depending on your coolant supplier.  

Engine oil on the other hand is chemically pretty stable depending on blend.  It is not uncommon for full synthetic oils to withstand as much as 150C.  So between 90 to 110C is kind of normal.  (195 to 230 F) Cold oil actually increases wear (long subject)  

So with that said crankcase oil temperatures will always be higher than at the sensor (especially on the carb engine where the senders are mounted at the coolest part of the oil circuit.  The iS has the oil sensor on the block reading the internal temp but again it is not at the hottest area relative to the total circuit.  Rotax only publishes the temperature rating that you would see at their sensor position. 

Cheers

Thanks RW,

Unfortunatly you have not really addressed the question.

I have gone to a lot of trouble to get my oil temp to a bit over 100 - 110C, in extended climb out.

In Crusie it can be as low as 90 - 97C (depending on OAT).

I know the above is well within Rotax recommended temps, however it struck me that I might just as well have left the T-O/Climb temp at 95C if the actual temps (in the oil tank ) was above 100C

Hi Sean

The actual requirement to get the oil above 100 C (212 F) is to drive out water accumulation from condensation.  The water can separate from the oil after it cools (on shut down) and leave rust on any iron/steel parts.  in the case of any leaded fuel use it may combine with the lead and form acids that can pit both aluminium or hard metal parts like valve seats and valves.  

Rotax is asking for an elevated temperature at the sensor to be sure it will burn off the water.  (yes it gets rid of other things also) The difference from inside the engine block at its hottest can be as much as 10 to 15 C from  the reading on the sensor.  Given there is no practical way to measure that we use the sensor reading in the 912/914 mounted on the oil pump body.  As soon as the oil is pushed from the block it is cooling in the oil return line which has a very high volume of air on return to the oil tank.  (blow-down gases) The entry to the tank itself cools in the air separation and swirl effect on the oil.  

Given it is a dry  sump oil design the crankcase does not have a position that you could check the temperature accurately.  on injected Rotax engines we place the temp sender in the rear oil galley of the block where it tends to read a higher temperature. This is a better position but not available for the 912/914 block. 

Just a note, the oil temps should not be in the lower range.  it is much better for the oil to run at the higher end than lower for wear and oil circulation.  You are most likely aware that lower oil temperatures will hang on to those other bits of materials that exist in your oil.  The best suggestion is still to run from 100 to 110 C in my opinion.  It is less the oil just never gets to purge it in normal running.  As a rule of thumb i like to see oil and coolant temperatures running near the same indicated.  Don't over-cool them.  

Cheers

Cheers

Many owners just use a 2" strip of thin aluminum tape (from a hardware store) across the oil cooler and or coolant radiator to raise temps during the colder months. It's cheap and easy to put on and take off and leaves no residue. NO NOT use Duct tape or Gorilla tape as those will leave a residue. Depending on how cold your OAT's are will depend on whether you use a 2" wide strip, 3" or 4", ect....