Constant Speed Propeller

"The 912/914 Illustrated Parts Catalog has oil radiator options as large as 234 CM^2.  The 912iS has similar options.  However, the 915 IPC offers a larger oil radiator of 300 CM^2, which is Rotax Part Number 886107.  I’ve seen some SLSA manufactures offering this larger 915 radiator on the 912iS engines.  If you don’t already have this, it’s another option for you to consider."

Hi Jeff,

Confirmed my oil cooler is the Rotax Large

Have emailed my local Rotax agent for the availability /price on the Rotax Extra Large Oil Cooler PN 886107 .

Do you happen to know if there is any data on the cooling performance of the  Extra Large compared with the Large?

Perhaps at my next oil change in about 20 hours FT.

Hi Sean,

I have a Bristell 912iS and it has the 234 CM^2 oil radiator.  A friend has the same plane that is two years newer and it has the same engine with the 300 CM^2 oil radiator. The oil radiator cooling air opening is also larger on his plane to match the larger size of the radiator.  Both aircraft have oil thermosts.   On our warmest days here in California I will see 238 deg f. on full power climb out and he will see 220 deg f.  At cruise on a hot day his oil temp will run about 10 deg f. cooler.  I believe the 300 CM^2 radiator is now the standard delivery for a new Bristell with the injected 912 engine.  I bought a 300 CM^2 radiator to make the upgrade but have not gotten around to it yet. This will require modifying the cowl, and my temps are not a problem, so I may or may not do the mod.   

Hi Jeff,

238F is just fine and normal for a  climb out where there is warm to hot weather. Up to 248F if need be. Here in Arizona seeing 235F -245F during the warmer months is perfectly normal. Your 220F in cruise and warm weather is fine too.

Thanks Jeff,

A drop of 10C would make quite a big difference in my situation.

My plan is to return my Sonex to my home workshop, relocate the coolant radiator, from exit air position, to front of cowl.

Relocating the radiator & associated baffling/bracketry, will leave an exit hole that will be about half as big again as the entry "nostrils". The exit air will be controlled by an existing  cowl flap (which may be deleted if found ineffective)

The radiator, in its new, front of cowl position, will have a dedicate air entry and be well baffled to cowling .

I am hoping that the combination of existing nostril + radiator air + better exit = much lower under cowl temperatures/air pressure.

A further option could be NACA (s) duct directing cooling air to ignition modules/carburettors.

The cooler air, exiting the cowling, will be sufficient to have a non baffled oil cooler in this stream of exiting air (not in the exit air hole).