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928 S4 Oil Pressure


New member
Hi All
Some advice please.
I am well into a sort of DIY restoration of my 928 s4 1990 during lockdown.

I`ve only done about 500 miles in her whilst I worked out what I needed to fix.
The engine feels strong and starts and runs very well.

So I`ve done the following :-

Suspension, brake lines and brakes completely replaced - no problems.
Engines plugs and ignition electrics inc most sensors all replaced - no problems.
Radiator, water pump and cooling fans completely replaced, evans waterless coolant and a lower temp thermostat - no problems.
Both fuel pumps and filter replaced, you won`t believe how much rubbish was in the tank - no problems.
Auto gear box filter and oil inc torque converter drain - no problems.

That`s was just some history but my real problem is as follows.

The volt meter, coolant temp and oil pressure gauges did not work so with all 3 being faulty I removed the instrument binnacle.
After a good clean the volt meter and coolant work perfectly, I`d already changed nearly every engine sensor so great.
I`ve also got a working oil pressure gauge but it`s the oil pressure that concerns me. It now works and below is what I get :-

At cold start it`s 5 bar.
When warmed up and driving along 2 -4 .
When warm and then sat at idle it drops and drops and gets to 1 bar after say 3 minutes ( engine already at temp ).
I then get a warning saying low oil pressure or words to that affect.

I`m running her on Mobile 1 0w 40 as recommended by Porsche but with 130K on her I`m thinking she may need a 50 or 60 oil.
Your thoughts please and thanks in advance.

Change to a regular 20W-50. Only -50 oils have the required level of ZDDP to protect these '70s engines.
And, you might not realize, but a 0W-50 will be thinner when hot than a 20W-50, "50" covers a range 45-55, so the 0W-50 might be a 0W-45 whereas the 20W-50 will more likely be a 20w-55.

If you continue with a thin oil, you risk scrapping the block due to thrust bearing wear or wearing out your cams.

Also, it may be that your oil thermostat isn't opening, check if the oil pipes to the cooler are getting hot.
The oil thermostat is known to have a limited life. BUT, change the oil to a -50 before doing any more investigation.
Have a look at this:

Basically, the pull on the drive shaft as it twists, pulls it backwards out of the clamp meaning that most of the time the shaft is pushing on the crankshaft via the flexplate. Releasing the clamp relieves the pre-load and means that the crankshaft thrust bearing isn't under constant pressure. The procedure also tells you how to measure the thrust bearing clearance. This is important to establish how worn it is, but not as important as releasing the pre-load to prevent future wear.

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