Flucuating Oil Pressure 912 ULS

I had the same problem and found in an NTSB aircraft accident report that restricted oil lines on the suction side can be the root cause for this condition on the Rotax 912. My factory original lines were marginally under to Rotax engine installation specifications including restrictive banjo fittings on the oil cooler. After enlarging the oil lines with fittings that do not restrict oil flow and replacing the ball with the mushroom type Rotax regulator, the fluctuating oil pressure issue was significantly decreased/almost gone/no longer a concern. This fixes/changes allowed the oil flow to increase so that it traveled thru the oil cooler too fast to be cooled down enough and the oil temps came up into the yellow/cautionary range on hot days at high power settings. The next step was to install the large Rotax oil cooler in conjunction with a Thermostasis brand oil temp regulator which resolved the high oil temperature issues as well as decreased oil temperature warm up times.

Thanks for the input.  Will follow up. 

Engine is flawless other than this problem.  No cooling problems. Needle bounces from 40 to 55 when acting up.  

my experience shows that The ball type and the new replacement by Rotax with the mushroom head which is the one on the left in the picture wobble around inside the oil passage. This causes the fluctuations....this new one pictured on the left the valve sleeve is held in place by the plug skirt and this solves the issue.
Fluctuations should be rectified but a relief valve is just that. It tries to limit it when a certain pressure is reached., depending on the spring tension. Thick oil can make it show a higher reading than the lift of setting., when cold if the engine is revved. You can't set for a cruise setting and the idle as well, as the idle will have the valve sealing (closed) so the oil viscosity and the bearings and pump condition will affect that. The flat faced end is unusual. Why not just have it located positively by the fit in the body and still have a slightly coned end ? A sliding plunger always runs the risk of a metal chip or something jamming it. Keep everything scrupulously clean.

Where can I get the flat headed plunger?  I have the mushroom headed one.  Last time I looked Rotax only had the mushroom headed one as the solution.

The Flat Head Regulator was invented by, and is only available from me.

The picture posted above was taken by me.  ( Appropriation is a form of flattery ??? )

Contact me via the Email Below.

Perhaps Garrett can comment on how his has been working the last few years.  <Hint, Hint>