Hi
My 01 XJR showed "Low oil pressure" when I started the car this morning. I stopped the engine and checked the oil level and it was normal. Not sure if it matters but the temperature outside is about -10 Celsius and I am running 5w-30 oil. Does anyone have advise on the situation?
Thanks

 

Temperature has no effect on this.

"Oil level was normal"....define normal pls. I run mine 1Qt over "Max". When was the last oil change? How many miles on the engine?

 

I think it's temperature dependent - if it's behaving ok, performance is there and no CEL's then don't worry, that's very cold for a cat

 

Normally you'd expect very hot oil to have a lower pressure due to the lower viscosity. On a freezing cold day the oil will be thicker & if anything would be more likely to open the oil pump pressure relief valve due to the high pumping pressure of cold oil.

When I start the engine in the Bentley on a cold day, the oil pressure gauge shoots up to maximum-even at a slow idle of 600rpm. Once the engine is fully warmed up you can see the oil pressure gauge needle dropping at idle speed to around half the scale.

Low oil pressure on a cold start on a freezing cold day may be due to the 'lag' of the cold oil reaching the pressure sensor switch-how long does the warning stay on for?

I've had plenty of oil sender switches fail in all my years of spannering cars-if the oil pressure was genuinely low then you'd expect the engine to sound noticeably noisier. Maybe the oil filter doesn't have the non-return valve & so it's taking a few seconds to fill due to the thickness of the cold oil making movement sluggish.

Only way to really be sure is to remove the oil pressure switch & connect a proper oil pressure gauge & sender to the engine.

 

I too am thinking its the pressure sensor and have already placed one on order. The engine fires up just fine and there is no change in the engine noise. I did not let the engine idle with the light on for fear of engine damage. I had restarted it again recently, and the light has gone out.
Thanks for the help

 

I previously owned a 1995 Daimler Double Six with a similar fault-the oil pressure warning would suddenly come on but there was no change in the engine note or noise & oil was still being thrown around the cam covers.

I suspected the oil pressure switch & that's what is turned out to be-I love a fault that only costs £5 GBP to fix

 

I am keeping my fingers crossed that it's a cheap fix

 

New sensor in and no more pressure light, cheap fixes are awesome

 

It is interesting that you would get a high OP on the Bentley -- most of my older MB's with true pressure gauges would show a lower pressure on very cold starts ups -- more of a slow to get to pressure .... now I am only talking about a few seconds.

With the introduction of synthetic oil this is eliminated.

Glad you found the problem -- are you running synthetic?

 

no I am running dino oil

 

The Bentley's oil pressure rises quite quickly from a cold start, although it's not instantaneous as the needle takes a couple of seconds to swing across the gauge-that could just as easily be the lag in the gauge itself I suppose.

 

I've had a few oil pressure senders fail on various Turbo Rs I've owned, so the newest one is a dual spade switch, with connections for both the warning lamp and the instrument itself. When using this type of switch (official Crewe replacement), it has to be "clocked" in a certain position for correct operation--that's how sensitive that system is!

 

Absolutely wrong. Stiff oil doesn't flow as well, sometimes to the point of pump cavitation. If seen engine failures over this on cold starts.
Running over the recommended fill can result in oil foaming and increased oil consumption from crank splash. The only possible benfit to this being a bit more oil to dissipate heat under marginal conditions, otherwise you're simply further enriching OPEC.
@ OP 5w ought to be adequate @ -10c but if the oil is old its additives break down and viscosity can be effected. If no other engine issues I'd begin with a fresh fill of quality oil.
EDIT: glad to see you fixed it

 

Under those cold conditions I would run 0W20 or 5W20 oil - glad your up and running...

 

Report back, have put about 400km on the car since the sensor change and have had no light come on. The car runs like a dream in the cold weather. I was -21 C last night and she fires up with no hesitation and idles super smooth. The oil in it now is fresh, in fact in the 4 months and 5000km of ownership I have done 2 oil changes (one when I got the car and the other about 1500km after when I did the tensioners).

 

Hey Winks. Having same problem here in NY. My mechanic recently changed my sender. But it didn't do the trick.

Is the sender different from the sensor or it's the same thing? Thanks.

 

I wish I could help you out on this one. I would look at the grounds and see if you have any wiring issues. If I understand correctly, these are fairly simple switches that are either switched on or off.