Dear All,

I have an ultralight air plane with 912UL mounted. Bought as used at ~400h. Now ~950h. Situation faced after replacement old used up VDO sensor with a new, also VDO type. Now with the latest version sensor version fitted. (thread reshaped from 1/8 NPT to M10x1 with very good thread cleaning)

There is a high oil pressure confirmed with different new sensors and gauges including a mechanical one.

After initial engine start with cold engine it is initially ~6 bar then goes slightly below 5 bar, lets say 4.9 bar during warm up.

During take off (WOT) (oil temp ~70 C) sometimes goes above 5 bar for short period (~5.5 - ~6 bar). Then after up to 10s stabilises very slightly below 5 bar.

Low RPMs - ~4.9 bar. middle RPMs - fluctuating, but within reasonable range (~3 - ~4 bar). Cruise power - ~4.9 bar.

Few 100h/200h maintenances done (oil with filter exchanges). 5y rubber parts exchange done twice, already. Oil always used: Aeroshell Sport +4. Fuel: Mogas.

Oil pump internal blockage checked - none. Still original ball instead of mushroom....

Crankcase pressure checked - 0.1 bar - OK. Engine is burping quite promptly.

Output power OK - performance like other same type aircrafts with such an engine (I have few colleagues with same aircraft type :) ).

Partially blocked oil lines? Shifted crankshaft bearings (not documented overheat by previous user)? Any ideas or solutions? Maybe exchange of ball into a mushroom (and new spring) would help?

I was even thinking about how to back flush oil lines: fill up crankcase with oil, seal crankcase bottom oil output, remove oil temp sensor or a whole pump and put some pressure via opening used for crankshaft blocking and watching what flows out....

ps. I have iRMT Line training.


  • Re: Rotax 912UL High oil pressure surely confirmed

    by » 3 months ago

    Why do you think you have high oil pressure?

    The Rotax operator manual states the following:

    • Max Oil pressure is 7 bar (102 PSI) (Oil pressure Max for a short period admissible at cold start)
    • Min Oil pressure is 0.8 bar (12 PSI) (Below 3500 rpm) and 1.5 bar (22 psi) if your engine S/N is 4 402 387 and higher
    • Normal Oil pressure is 2.0 to 5.0 bar (27-73 psi) (Above 3500 RPM) and 1.5 bar to 5.0 bar (22 psi - 73 psi) if your engine S/N is 4 402 387 and higher


    You are 100% within the normal operating range and sometimes go above (6 bar) during warm-up which is 100% normal! Our professional opinion is to leave it, fly it, and don't try and fix a problem that doesn't exist. Worry about your maximums and minums and don't worry so much about the "normal" range


    Here is the link to the Rotax Operators manual - See section 2.1 Operating limits (912 A/F/UL) page 2-2


  • Re: Rotax 912UL High oil pressure surely confirmed

    by » 3 months ago

    Hi Rotax-Owner,

    You are right. The oil pressure is within limits, but... But this engine is simply behaving different than others I had met. I fly many Rotax equipped aircrafts (certified and UL/LSA) as an instructor an make Rotax engine line maintenance to UL ones. This one simply behaves in this subject different than others. Although generally in limits.So I decided to ask on this forum as my experience is smaller as cumulative one of the whole forum users together.

    Anyway, thanks for your recommendation. It lowers my doubts.

    ps. I perfectly know the content of current OM, IM, MML an also MMH docs.

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