OIL PRESSURE on 912 UL engine

Let me confirm please.... The oil pressure drops when rpm is raised above idle speed by at least 50kPa then returns to 250kPa .

The fact that the pressure drops when rpm is raised,THAT is the part that bothers me.

Any idees please? I did check the houses on the suction part of the pump, expected a collapsed pipe but nothing found there.

Kind regards.

IMO, the Rotax Oil Pressure regulator is crap and the usual VDO oil pressure senders (from a VW beetle), likewise. The somewhat-improved version (841983 "bolt with recessed head", piston (instead of ball) 857230, and spring 838122) is probably worth installing for starters. With a fully-electonic remote-mounted (not bolted to engine) sender replacing the VDO, and cross-checked with a mechanical gauge, one can really see what's going on, and it isn't pretty. Many threads on the subject, which you can get into by searching the site for "857230". You didn't specify the rpm's at which this drop happens, but at low rpm's, and especially without fully-warmed oil, the pressure readings behave weirdly on my setup too, but always remains in the green range.

What's to worry about, is when the OP drops with increasing rpm in flight mode, say 3,500 - 5,000 rpm, and down into the yellow range. That's the suction line hose collapsing! Once collapsed, it will stay collapsed, even when rpm is reduced to near-idle. You will *not* be able to see this problem on the ground. "Condition inspection" cannot be done on the suction hoses; they must be replaced as recommended. <Insert bitter experience>.

This type of pressure drop when rpm is increased and then goes back up when brought back closer to idle is usually caused by a poor ground. You may have a ground, but a poor one. The first time this happened to me many years ago it drove me nuts for 2 hours. Then I used a wire with some alligator clips and bypassed the original ground and the problem disappeared. So I installed a new ground wire for the gauge and the problem never came back.

This is very easy to check. Just temporarily hook up a wire to a known solid ground and then to the instrument and then do a test run.

Thanks, but grounding is not the problem in making this observation; clip leads, 4 different senders and cross-checking with a mechanical gauge leads me to conclude that this engines OP response at low rpm is just plain weird. (I'm not arguing that grounding could be a common issue in general, to be clear.)

Hi Jeffery

i may have encountered what your going through.   Mine was an early 80 hp 

and I updated the oil pump to the new relief valve from the old ball and spring.

As soon as I did this I saw oil pressure drop with rpm increase!  

  I modified the new oil pump plunger to allow more oil to pass by.  

I cut three flats on the large diameter, of the plunger to bypass more oil  around the plunger.

I believe the bore  the plunger rides in is too small on the older engines, which

when the plunger opens,is overpowered by the oil. ( the plunger has much more surface area

than the original ball)       Did this mod and my oil pressure was back to normal instantly.