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Low oil pressure

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Paul Fraser

New member
Started a banger I bought (944) for the first time in about three-four months with a view to getting it MOTed (it had a assymetric brake problem which I think I've cured by refurbing the inner workings of the right hand caliper).
Noticed at the end of a short run to test the brakes that the oil pressure light was flickering and oil pressure very low. Stopped engine and dipped oil and there seems to be plenty there.
Part of the problem is the low idle, it seems to be on the verge of stalling when idling -- about 600 rpm (how hard is it to sort this?). When increased manually to 800-850 the oil pressure is barely 1 bar. At 4000 revs the pressure rises to about 4 bar and there is a fair bit of dark grey smoke coming out of the exhaust. I assume this is the piston rings?
Thing is, I'm pretty sure it didnt have this problem when it was last run three or four months ago. Could this be layup related?
Will a bottle of that smoke-stop stuff help any? TIA
 
The pressure at idle will be lower than at speed so an ultra low idle of 600rpm will bring about a super low oil pressure. Once warmed up and at the usual 850-900rpm it should be around 3 bar, at speed it should be between 4 and 5 bar, with as close to 5 bar being the ideal.

Of course all of this is dependant on your oil pressure sender being sound [;)]
 
Sounds a bit odd 3bar when warm is fine, it sounds like a sender problem. Did it start to happen after you changed the sender or before?
 
Sounds like pressure relief valve failure on a series one oil pump. You can fit the later series two (September 1985 >) part to rectfy it for good.

A good diagnostic step would be to increase the tickover speed very slightly, if the oil pressure jumps up by a couple of atmospheres then Id be certain.

Simon
 
At cold idle oil pressure is high - 4 - 5 bar. When warm at idle 3 - 3.5bar is fine and under power 4 - 5 bar. Does this sound like what you're getting?
 
One bar on cold tickover but higher pressure when its ticking over warm indicates that the PRV is opening under (too low a) pressure.
 
Sounds more extreme than mine, but if I drive hard on a hot day I can see the oil pressure drop down to 1 bar at idle. Manual says anything above 0.5 bar is OK.

What oil are you running?


Oli.

ETA: Are you sure it is genuinely low pressure rather than a faulty gauge/sender? If so, how?
 
...hot day I can see the oil pressure drop down to 1 bar at idle. Manual says anything above 0.5 bar is OK.
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I would suggest it's the heat - they can run pretty low and still be OK. It's probably had a shock (like everyone else at the moment), in that there is actually some heat in the air.[:)]
 
Sounds unusual after just 15 mins of driving - should be ~4bar @ 4k rpm

OPRV is a very expensive part - nearly £300! I have just swapped mine for the opposite reason as it appeared to have stuck shut twice at Bedford, causing a lovely oil slick.
 
The gauge on my turbo used to drop slightly when on boost - after testing with a separate sensor and gauge, we decided that it was actually a dash wiring fault, so as the boost gauge rose, it affected the oil pressure gauge.

The OPRV is supposed not to be rebuildable, although not sure why. I've kept my old one in case anyone ever decides that they are...
 
Sounds exactly like the symptoms of a loose crankshaft pulley bolt to me, and right kind of figures for it too, but that doesn't mean it couldn't be anything else!
 
this is a must read:

pelican low oil pres

long story short my money is oprv either seal or something blocking it!

also if your lifters sound a little rattley at idle it rules out any sender fault - do they?
 
Thanks for all of the thoughts chaps! [8D]

Oil is 10W/40 semi-synth from memory. There is no rattles or any other unusual noises. I'd be surprised if it's a weather/temp issue I think. I've not had similar on hot days before and this morning I only drove for 15 minutes and it was warm but still cooler than other hot afternoons I've driven in.

I've been around to Rob's and borrowed a flywheel lock - I'll check the pulley bolt in the morning plus he happens to have a spare OPRV (it may not be the same as mine) to swap over and try if it's not the crank pulley bolt. I already have the O-ring for the OPRV so that's good!

Well it looks like the MK1 Golf wont get a look-in tomorrow, will investigate the 944 and update [;)]

Thanks again

Andy
 
Good luck with the Flywheel lock......


BTW it could actually just be a duff sender unit, this happened to me and a quick swap out fixed it !


I think Rob is doing whats called sub contracting....
 
If it was the crank pulley bolt you would have the same readings from start up i would have thought as the tapered drive would not be engaging hot or cold with a loose crank bolt, i would have a guess at wiring, does the gauge show low and the light come on together ?
Oil pressure sender ?
 

ORIGINAL: chrisg

Good luck with the Flywheel lock......


BTW it could actually just be a duff sender unit, this happened to me and a quick swap out fixed it !


I think Rob is doing whats called sub contracting....
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Sorry Chris - I did mean to say some thanks to you - Rob did say it was yours - I hope you don't mind the subcontracting, it will be taken care of [;)]

Ref the sender, I thought if this fails then the gauge reads 5 bar all of the time?

The oil pressure light only comes on when symptoms have started and the car is at idle, otherwise when driving the pressure is lower than usual - 2.5-3 bar but the light does not come on
 
Guys the pressure sender has two functions. It is a variable resistor to indicate actual pressure on the gauge and also a switch to indicate low oil pressure. They will normally fail high. Besides it is probably as easy if not easier to change the OPRV seal and hence check it at the same time as it is to change the sensor. At least by doing simple and let's face relatively low cost or even free checks first like the o ring and the crank pulley he can eliminate all of these things before he needs to shell out any real cash, or perhaps even find the problem. If the crank pulley bolt was loose and not completely undone as in your case Frenchy it could feasibly be slipping and still provide some but not maximum drive to the oil pump. It could feasibly rise but still read low.
 
Keep us posted on your findings Rob, hopefully something simple, usually is (fingers crossed)
 
Well I just thought I'd try the theory about the weather. I sat on the drive, turned the engine on and let it get up to temp. Then sat idling for about 10 minutes. Oil pressure started at 3 bar then eventually started to drop to 2 bar, then a bit lower. Then the needle would intermittently flicker up and down between 1 and 2, sometimes lower and the red low pressure light flickered on so I turned off.

It's still warm out, but not that warm. Oh and I checked I use 15w/40 not 10w/40 oil!

Will be trying crank pulley bolt then OPRV first thing in the morning then!
 
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