Dry Sump Siphoning Issue - Fixed

[JeffersonRaley]

<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.

[TurboWood]

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

[JeffersonRaley]

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.

[TurboWood]

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.

[TurboWood]

Bringing this back from the dead as I had an interesting thing happen. My oil filter/cooler attaches to the block at the left rear corner, near the top of the block. It is fed by the factory oil pump which draws from my dry sump tank. Effectively this means there is a hose from the bottom of my oil tank to the factory in-engine oil pump.

Last weekend I needed to disconnect the filter/cooler to diagnose/fix a leak. In the process I pressurized (with a bicycle pump) the fitting on the block which is the output of the oil pump. This forced the oil back into the oil tank. After doing that my oil tank has remained full. This was a surprise to me since the gravity/head-pressure of the oil in the tank is obviously still there.

Why didn't my tank drain like normal? Is it a siphoning effect that has been avoided by having the filter/cooler disconnected?

Daniel

[speedwagon]

Bringing this back from the dead as I had an interesting thing happen. My oil filter/cooler attaches to the block at the left rear corner, near the top of the block. It is fed by the factory oil pump which draws from my dry sump tank. Effectively this means there is a hose from the bottom of my oil tank to the factory in-engine oil pump.

Last weekend I needed to disconnect the filter/cooler to diagnose/fix a leak. In the process I pressurized (with a bicycle pump) the fitting on the block which is the output of the oil pump. This forced the oil back into the oil tank. After doing that my oil tank has remained full. This was a surprise to me since the gravity/head-pressure of the oil in the tank is obviously still there.

Why didn't my tank drain like normal? Is it a siphoning effect that has been avoided by having the filter/cooler disconnected?

Daniel

if the filter base is below the oil level in the tank--yes as soon as you raise the output hose higher than the fuel level in the vessel you are siphoning from flow stops. Learned that as a youth getting "discount" gasoline.

[TurboWood]

I suppose this means I could put the check valve on the oil filter/cooler line then. This should keep my tank full and only create a 1-2psi drop in oil pressure feeding the engine.

Daniel

[speedwagon]

In my previous post I meant to say-- if the filter base is above the level of the oil in the tank yes it would break the vacuum. and as far as cavitation is a concern- gear pumps generally do not experience this. (remember in the old days before we had a shaft to run the oil pump before starting a fresh engine the pump would pull the air out of the system at start-up. my worst fear would be a tossup between a stuck closed check valve(not likely at the low pressure) and a hydro-locked engine. john am editing this post after reviewing the original data----EDIT if you force the oil back from the high located filter and reconnect it; there will be no siphoning because there is insufficent weight of oil in the line down hill from the filter to pull the oil from the tank uphill and through the filter. Sorry for misreading the original post (must be a product of age). john

[xcarguy]

John,

Different animal, but FWIW, I'm runnjng a check valve on the downstream side of my oil cooler with no oil preasure reduction issues.

[speedwagon]

John,

Differrnt animal, but FWIW, I'm runnjng a check valve on the downstream side of my oil cooler with no oil pressure reduction issues.

It has been a few years since my "instrumentation" days. But a check valve in a flow line is effectively an orifice plate and will reduce pressure "down side" for only a short distance. (you can look up orifice plate and get the exact formula). and check valves are commonly used in applications that require limited flow reduction. My only reservation would be the quality of the valve and design of the mechanism. Wouldn't be a buying any offshore junk. I would not hesitate to use one but as for anything in the lube system it would be of the highest quality. this is one of my favorite sites to read because of the friendly, helpful nature, and amazing volume of knowledge here.
john