Long Wait for Oil Pressure

marojojoem · Mar 8, 2020

Hello I'd like some advice on a problem with my 86 Turbo.
When I start after the car has been standing for a while it takes way too long for the oil pressure to build. I reckon the light stays on for 5 to 10 seconds accompanied by some clatter from the top end. Once running I get 5 bar at idle when cold and 3 bar when warmed through and no untoward noises.
I imagine that the oil is draining back to the sump so that the pump takes a while to refill the system.
Any thoughts as to where to start with this issue.
Thanks in advance
Mark

bmnelsc · Mar 8, 2020

First thing I would look at is the oil filter. Are you sure you have an OEM type filter (Mahle for one) specific to the 944? 944 specific filters have a check valve to stop the oil from draining out of the filter when the engine is off - this saves having to refill the oil filter before pressure can build up. Not every aftermarket filter that will fit the 944 has a check valve as this is only needed when the filter is installed "up-side down" as on the 944 - filters installed with the can side down don't need a check valve as the oil could not drain out.

If that is not the problem then you may have a stuck oil pressure relief valve (valve stuck in the open position so oil pumping around freely until pressure finally builds up). This is the one near the oil cooler console...best check your manual for details.

PSH · Mar 8, 2020

I agree with Bruce... have you recently changed the filter for a non-OEM type, this is a well-know cause of such issues...

Pete

marojojoem · Mar 9, 2020

Thanks Pete and Bruce.
That was my first thought too but the filter was changed during a service last year by a very reputable independent specialist and the invoice lists the part number for the OE filter. I could just change it anyway but I suspect the one that's fitted is okay.
I will have a look at getting to the pressure relief valve to see if it is jamming open but I'd expect that problem to cause low oil pressure at idle?
I think plan A is to leave the car standing for a few days and remove the filter to check if its got oil inside and go from there.
Thanks again for your ideas, any further thoughts welcome
Mark

944Turbo · Mar 9, 2020

I believe there is some form of non-return valve in the head to stop the oil draining down, Not sure how bad the pressure situation gets if this fails open and lets oil drain out,
Tony

PSH · Mar 9, 2020

Hi Mark

I would still take a close look at the filter, is there such a thing as a 'reputable independent specialist' if so, I haven't come across one during my 23 years of ownership. Only use a Mahle filter would be my advice, there have been a number of reports over the years that this is the only filter that does the job properly.
Tony's point is also valid although I think that I've only read of one case of this being the cause and IIRC this was after an engine rebuild. It could perhaps also occur if the car was recently bought with no history and not had an oil change in the last few decades, ie, it's been badly maintained. Not that this is the case here.

Pete

marojojoem · Mar 9, 2020

Thanks again Pete, I will have a close look at what Ive got fitted and report back in a day or two.
Interesting Tony that there is a non-return valve in the head, maybe one the consider as Plan B
Mark

Waylander · Mar 9, 2020

if its in the 944 8v head, its at the rear by no4 exhaust valve, a spring a ball bearing and O ring,

the O ring tends to go rock hard and fall to bits letting the pressure out,

PET Says
N 025 669 2 Ball @98p
928 104 129 00 Spring @92p
951 104 229 00 Guide @£5.27
999 707 078 40 O Ring @£5.10

for Head Part number 951 104 038 02
engines 4450,4451,4452

the whole unit is available at 944 107 239 01 @ £311.86

marojojoem · Mar 9, 2020

Right that's really helpful, sounds like its worth doing anyway
Mark

TTM · Mar 12, 2020

944Turbo said:
I believe there is some form of non-return valve in the head to stop the oil draining down, Not sure how bad the pressure situation gets if this fails open and lets oil drain out,
Tony

When starting a cold engine with the one way valve uninstalled the oil pressure gauge should read around 3 bar instead of 5+.

944Turbo · Mar 13, 2020

TTM said:
944Turbo said:

I believe there is some form of non-return valve in the head to stop the oil draining down, Not sure how bad the pressure situation gets if this fails open and lets oil drain out,
Tony

Click to expand...

When starting a cold engine with the one way valve uninstalled the oil pressure gauge should read around 3 bar instead of 5+.

Interesting I was wondering if it could be there but not seat correctly either through damage to the ball or swarf / gasket /carbon on the seat. Is the extra pressure generated by pushing against the spring or just the lack of oil in the head?

TTM · Mar 13, 2020

As I did this test a few years back, oil pressure would gradually go lower from 3 bar as oil temperature would go up, without seemingly starving the camshaft housing from lubrication.
To me this means that the one way valve in the head is so restrictive that it contributes to the oil pressure in the bottom end.