918-S

Some may remember awhile back I posted I was having an issue with my oil pressure. I have a fresh 5.0 Hybrid built with a bored out 1980 euro "S" M28/11 block, heads and CIS. The engine has about 15,000 miles on it now.

I was traveling at freeway speed when I noticed my pressure drop from + 80psi to 40ish. The pressure popped back up then back down. I got off the freeway. When I stabbed the clutch to down shift on the ramp the pressure fell off with the drop in throttle. Long story again but I ended up flying home and traveling 600 miles to get the car with my trailer.

I had the oil tested and posted the results here awhile back now. No metal or anti freeze in the oil and the results were normal. This leads me to believe I do not have a spun bearing or any other friction failure or issue.

I thought I may have a loose pickup tube. I just dropped the pan to check. The pickup tube is fine and all looks normal. I discovered I had a kind of sludge in the bottom of the pan. For a 15,000 mile engine this didn't look normal. The sludge is thicker than the 20/50 Castrol GTX I usually run.

As I was cleaning out the pan looking for anything that may be out of the ordinary I discovered a sand/flake like carbon in the sludge. It's hard like a grain of sand unitl you roll it between your fingers. Then it crumbles.

Q.) What would cause this carbon in the bottom of the pan? The inside of the block looks perfect and clean.

Q.) Is it likely this carbon is getting into the pressure relief valve causing it to stick and drop pressure?

Q.) Where does the oil go when it leaves the pump?
1) Through the filter?
2) Through the pressure releif valve then to the filter?

BC

Very strange. When the pump gets too clogged, it gets bypassed as I
Am sure you know.

If that sludge has somehow occasionally gotten sucked up it could also affect the oil
Pressure.

It goes from the pump, iirc to the mains first. The filter may be in that loop somewhere. Someone will correct me if I goofed on that.

The oil pump is the next possible thing to remove. Find out if that sludge and granular material is in that.

Someone will post the oil circuit picture I am sure.

I am thinking about the pressure relief valve. Did you replace that spring?

918-S

Thanks for the reply. Ya, a oil ciruit diagram would be helpful. I have not replaced the spring yet. I just cleaned and reinstalled the oil pan.

I'm going to pull the spring and piston tonight.

rbrtmchl

This link has the oil flows for both 16v and 32v.

https://rennlist.com/forums/928-foru...w-diagram.html

918-S

Thanks, That kind of confirms the chain of events. Because of the limited space in my engine bay I eliminated the oil cooler and moved my oil pressure sender up to the top cooling line location. I gutted the cooling line T Stat so it's just a hollow chamber where the cooling lines attach.

So, If # 3 valve is hung open the oil circulates back to the pump and not to the second pressure valve, cooler line location or filter. If the carbon/sludge is sent up through the pump it's the first place the it ends up. Hmmm...

Glenn Evans

I haven't seen your earlier thread (I'll look for it after posting this). You haven't said that you've changed the filter. There is a bypass valve in the filter, which allows the filter element to be bypassed when the pressure drop across it is around (from memory) 2 or 2.5 bar. This occurs when the oil is cold and if the filter is clogged. A sludge buildup in only 15,000 miles indicates that something is wrong. Should the operation of the filter's bypass be impeded by that hard deposit (although this seems unlikely), your oil pressure will be affected.

Apart from the engine's bypass valve (as suggested previously), the other cause of the low pressure could be the oil pump being starved. You have said that the pickup is secure and looks OK (I presume that means the screen is clean), so I suggest that you concentrate on the filter first. Cut it open (or the used one if you have changed it and still have the old one), look for deposits and check the operation of the bypass valve.

Have you had the sludge analysed? The oil must be getting contaminated by something. Are you sure it's not coolant? Do you use any aftermarket oil or fuel additives? How many oil and filter changes have you done in that 15,000 miles? In Australia around 2000, I heard from a couple of mechanics that there had been numerous cases of oil turning to gel in new cars with long oil change intervals (15,000 miles plus). This was associated with a particular brand of premium unleaded gasoline and was kept out of the press. I mention this as something to keep in mind if no other source of contamination or reaction with the oil can be found.

Maleficio

You and I are thinking the same thing. Here's my ideas:
http://forums.pelicanparts.com/porsc...-question.html

RKD in OKC

Every time I've had wonky oil pressure it was the oil pressure sensor, connector, or wire.
Done anything in that area recently, oil filter change?

Glenn Evans

I agree that faulty oil pressure indication is very likely! Should that be a problem here, though, it's fortuitous that it has led to the discovery of the oil sludging and deposits.

Glenn Evans

Regarding the hard deposits, did you have anything, such as the intake runners, grit blasted to clean them? Given that your hard grit crumbles, it probably is not residual blast media, but if it were, it wouldn't be the first time that some was missed when the engine was cleaned.

918-S

I cut the filter apart and used the oil in the filter for the testing. Here's the results. According to the chemist nothing unusual, no metals, water or coolant.

918-S

Oil changes around 3K or before every road trip. From MN to Huntsville AL and back with the fresh engine. So fresh infact that I stopped at a quick oil change place about 500 miles into the journey and had them change the breakin oil. I had them put in my 20/50 Castrol. With running the twisty roads in Al total mileage around 2500

MN to Hershey PA. and back. Oil changed before we left. About 2500 Miles

MN to Grand Junction through Monument National Park with some real crazy Porsche guys. We should be in jail... Fresh oil before we left. With running through Monument and the back road there about 2800.

Then my second trip out west to Moab. I made it to Lincoln. That's where I started having trouble with the pressure. This one way trip is about 700 miles.

Verious trips around here. Looks like under 10,000 miles.


I checked the gauge wiring when I noticed the malody. I heard a lifter start to tick that's when I stopped messing with it and decided it costs way too much to hurt the engine and decided to fly home and get the trailer.

I don't know about the filter. I always use Mann. Infact I just finished checking the pressure relief valve and replacing the spring. (anyone ever try that with the engine in the car... hand cramp!) I went to look for my spare filter but I'm out. I'll have to wait to order one so no action until Probably Tuesday or later in the week.

BTW: I had two aluminum crush washers under the relief valve cap. This could have caused a early opening of the valve. I have a 150 psi gauge and the car always pegged the gauge when cold. Hot it runs 80-90 psi.

Glenn Evans

Do you realise that your oil was out of grade ie the viscosity is too low? To be 50 grade, the kinematic viscosity must be within the range 16.3 to 21.9 cSt at 100 degrees C. Yours is 14.9 (40 grade). Either the oil is diluted (possibly with fuel) or it has been overheated and the viscosity improvers have become ineffective.

918-S

Interesting Glenn. I did not notice that. Hmmm. My concern was the metal, water or coolant content. Could have been cooked. Could explained the carbon. I wonder what the heads look like under the valve covers. I pulled the relief valve last night, cleaned it, replaced the spring with another one I had. I still have a cramp in my hand this morning from pushing the thing in while turn it. I thought I had a spare Mann filter but I must have used it. So I won't be able to test fire the engine until next week sometime. Thanks for the input on this,

Still, low viscosity would not translate into a drop in pressure to the point of zero pressure. But a chip of carbon hanging the pressure valve open may.... no?

Oh, I failed to mention when I pulled the cap off the spring I discovered I had two aluminum crush washers. I wonder if this could have aggervated the problem by decreasing the pressure on the spring.

Glenn Evans

The extra crush washer certainly would lower the opening pressure of the pressure relief valve, but I don't know by how much. It doesn't explain the fluctuating pressure, though.