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My 325 hr ULS used to make oil pressure just turning over on starter (mags off).
Now I get no pressure at all whilst turning over (Even with top plugs removed) and then takes a while to make pressure with engine running.

This happens if it has sat a week or two.
Once I have pressure, which reads good, I can start and stop all day with instant pressure but the problem at first start up seems to be getting worse.

Fitted a mechanical gauge today to confirm this and also found I have the "ball" valve.

It seems like the oil pump has lost it's prime and is struggling to suck it from the tank. Is this possible?

I plan on getting the "mushroom" valve kit and will purge the oil system with air pressure.
  • Re: ULS struggles to pull oil press on start up.

    by » 8 years ago


    A couple of things come to mind.

    Are you using a Rotax oil filter (this may be a stretch, but worth consideration if it is an off brand)
    Have you worked on any part of the oil system?
    Possibly the sender?

    Changing out the oil pressure plug screw, spring and mushroom may be just the thing you need.

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell


  • Re: ULS struggles to pull oil press on start up.

    by » 8 years ago


    Filter is Rotax. 25 hrs old.

    I removed a thermostat in the oil system at last oil change, 25 hrs ago. Fitted Alu tube joiners and purged as per procedure.
    Oil lines etc are pretty much in the same position as before.
    Thermostat was removed as I was getting high oil temps which I now put down to summer temps and a rather coarse prop.

    Mechanical gauge proves oil pressure is not "picking up".
    At first I thought it was the honeywell, that's why I put the mechanical on it.

  • Re: ULS struggles to pull oil press on start up.

    by » 8 years ago


    Hi Rhett,

    Is your oil pressure sender a remote mount? Just considering air in the line.

    Since you have done this done these checks then I would suspect the old oil pressure plug screw, spring and ball bearing setup and swap the parts out.

    The other think it may be is an air pocket. It's just suspect. Just keep this one in the back of your mind if the oil plug screw, spring and mushroom swap doesn't work.

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell


  • Re: ULS struggles to pull oil press on start up.

    by » 8 years ago


    Yes Roger, I was thinking an air pocket of some sort but thought it would have been pulled through the system once oil pressure eventually came, and not returned. And the purging should have cleared it.
    The oil cooler inlet and outlet are both on the bottom of the unit and I have always thought it was a poorly designed installation prone to form an airlock But it is a factory install. I did unmount it and turn it up when purging.

    I don't see any oil leak, but if air was able to get into the hoses/cooler then I guess the oil could run back to the tank causing the symptoms I'm getting.

    Should I be able to see oil pressure on just the starter? Is this common/normal?

    Oil pressure not remote mounted.

  • Re: ULS struggles to pull oil press on start up.

    by » 8 years ago


    If the oil pressure sender isn't remote mounted there is less likely an air pocket issue in a hose. I suppose each aircraft is plumbed a tad different for oil lines. You may or may not see the oil pressure with just the starter. I would not worry about that at all. You should however have oil pressure within a couple of seconds on start.

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell


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