944 Oil Pressure Relief Valve

Background:

Within the 944 series cars, the oil pressure is regulated by both speed of the engine as the engine drives the oil pump, and by a pressure valve.  This valve (expensive BTW) is an area of failure that seems all to common in our cars.

There are two kinds of these valves, a 3 piece unit and a 1 piece unit.  The three piece unit was used up until Model year 86 inclusive (according to my dealer) and in 87 it was replaced with a 1 piece unit.  The 1 piece unit uses o-rings to seal it, and the 3 piece unit doesn't, and is a direct retrofit replacement for the older kind.

Make the assumption that you have the 1 piece unit, and get the two o-rings from a  dealer PRIOR to starting this job.  They're cheap - and it would really stink if you didn't have them available to re-assemble, and you were going to the track the next day.

Diagnosis:

A failing or dirty pressure relief valve can cause many symptoms, from higher than normal oil pressure (valve stuck closed) to low oil pressure (valve stuck partially open.) to no oil pressure (valve stuck totally open.).

My car exhibited oil pressure of 1 bar on the stock gauge at idle, and 2/5-3 bar at cruising speed.  My oil pressure light flickered at times, especially when the car was at temp and I was at idle.  Normal oil pressures for these cars seems to be around 2-2.5 bar at idle, and 4.5 or more at cruising speed.  I was using Mobil 1, 15W50 oil, and Porsche filters.

Other possibilities for low oil pressure include a bad oil filter, a blockage in the oil channel lines, low oil, a not tight enough crank bolt (155ft pounds or more), lack of a rubber o-ring behind the washer on the crank that drives the oil pump, a bad oil pressure sender, and a failing oil pump.

Cleaning the pressure relief valve is simple, and can eliminate some of those possibilities.  When in doubt - ALWAYS have someone with a mechanical oil pressure gauge check the car.  That immediately can rule out a lot of components (sender, pump, gauge, etc.)

Tools:

1. A 22 or 24 MM socket and wrench, with a 1 foot extension if you're using 1/2 inch sockets or have big hands like me.
2. About 15-20 minutes time
3. 2 o-rings, which can be had at any dealer (ONLY if you have the updated
   1 piece valve that is...)
4. Jack stands, and a good jack
5. A torque wrench - capable of at least 33 ft pounds.
6. Rags to catch oil drips as they come out of the hole that the valve was in.

Procedure:

1. Jack up the car on the passenger side (US spec that is...) so that you can get under where the oil filter is.
2. Support the car with jack stands
3. Climb under there, and locate the valve.  It's the 22 or 24 mm bolt head located right under the oil filter.
4. Remove the valve.  It's not that tight (33 ft pounds I think), and it easy to get at.
5. Clean said valve.  If you find that you have the 3 piece older style valve, now's a good time to update to the newer valve.  Be aware though - the dealer lists it for about 230 bucks US.  Make sure that the piston travels smoothly in the bore, and that there's no gunk on the valve.
6. Replace the O-ring at the tip of the valve, and the sealing ring at the bolt head end.  (This assumes you have the 1 piece valve...  From what I hear - the 3 piece unit doesn't use the O-rings.)
7. Replace valve.  (If you like - you may rotate the engine here a rotation or two to insure that oil comes out of the hole)  It does go all the way back in.  I had to fiddle with it for a minute to get it in all the way.
8. Tighten the valve to 33 ft pounds.
9. Lower the car.
10. Start-er-up.

Notes:

1. If you see ANY gunk on the valve - I'd suggest an oil change at the same time - just in case.
2. Make sure you don't have any wear on the valve itself.  There should be slight resistance when you press the piston in the valve body.  My valve had gunk on it keeping it partially open.
3. Coat the valve with engine oil prior to re-installation - just in case.

Credits:    Jay Cohen