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Thread: Dry Sump Siphoning Issue - Fixed

  1. #1
    Join Date
    Nov 2013
    Posts
    60

    Default Dry Sump Siphoning Issue - Fixed

    <Caveat - not my fault if you grenade a motor>
    I have had an ongoing problem with the dry sump tank my Seven draining back into the engine when parked. This fills the engine with oil up past the crankshaft. When you start the car it creates all sorts of oil pressure in the bottom of the engine. The rear main seal was never designed to hold back pressurized oil, so it leaks.

    This is a pretty common issue with dry sump systems. The oil actually siphons through the feed line, into the oil pressure pump and on into the engine. Since the oil is siphoning in the same direction it usually travels, a 1-way check valve wouldn't normally be the solution. People solve this in all sorts of ways, but the common ones seem to be:
    1) Lower the oil tank below the crankshaft (not practical in a low car)
    2) Install a manual or electric ball valve to cut off oil flow when parked (dangerous and a pain in the neck for a street car)
    3) Live with it (some cars don't leak all that badly, but mine does)

    I took a different route, and it seems to be working. I installed a 1-way check valve, but I did it in the direction of normal oil flow. So basically the check valve is preventing oil backflow (something that never happens). The trick is that the check valve requires 2 psi to open, which is enough to stop siphoning when parked. I'm using a 12AN check valve from Summit Racing that is typically used in fuel systems, so it is oil safe (generally if seals can live with gasoline, they can live with oil). No drop in oil pressure and the siphoning has stopped.

    Potential Downsides:
    1) If my pressure drops to 2 psi it will immediately drop to 0. But at anything below 10 psi I would already need a new engine.
    2) Oil flow might be slightly restricted... maybe... in theory. But my oil pressure is 18 psi at idle when hot off the track, so the check valve is wide open. 12AN is 3/4" inner diameter, so plenty of oil is flowing (you can see it pouring into the tank).

    Note - I'm using the AT Power dry sump. If I had it to do over I'd probably go with Raceline because their oil pump is integrated into the pan, so much easier to install. But the AT Power unit is billet aluminum and oh so pretty.
    </caveat>

    Hopefully someone else will find this useful and saves someone else the time I spent figuring this out.

  2. #2
    Join Date
    May 2013
    Location
    South Bay, CA
    Posts
    263

    Default

    Nice post. I'm definitely seeing the same drain back issue. I don't now yet if it will cause any issues for me, but I would certainly prefer the oil tank to stay full of oil. I assume you put the check valve between the high pressure pump and the engine? In my case that won't work because I'm using the factory oil pump (crank driven inside the engine) fed by the oil tank. I wonder if anyone makes a 0.1psi check valve?

    Daniel

  3. #3
    Join Date
    Nov 2013
    Posts
    60

    Default

    I put it on the line that feeds the oil pump from the tank. So I think you can do something similar. I'd take a picture, but everything is apart because I'm pulling the motor this weekend.

    The 2 psi opening check valve was just about the lowest I could find. I did find an industrial one that opened at (IIRC) 1 psi, but they weren't really set up to sell to consumers.

  4. #4
    Join Date
    May 2013
    Location
    South Bay, CA
    Posts
    263

    Default

    hmm, that does raise the risk of cavitation. I suppose so long as you are getting good oil pressure out of the pump then you are ok.

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