Sag oil pressure at idle when really hot

[Englishman]

Just interested if anyone else gets an occasional flashed up 4psi warning of low oil pressure on days like today when idling stuck in traffic with air con etc. adding load. Tried changing the pressure relief valve spring but no difference. The oil is topped up to the max mark and can up the idle rpm a bit to stop it, but any ideas of the cause?

[NailedOn]

I get the same in my T350c.
I have a new alloy radiator and fan thermostats, but when stuck in a queue the water nudges 98C plus, the oil 85C plus. The oil pressure floats below 10psi when stationary.
Once moving, it quickly rises.
I checked with my dealer and all is OK.
I am pretty sure that your Sag is likely to be the same.

[DonkeyApple]

Yup. My 3.6 would dip to 4.

Pressure is really low on idle. It's not great as a design but it is normal for these engines.

I believe the ones with the reworked oil ways have better pressure.

Mine on the new 4L engine never goes below 40 at idle now and is very constant when in use without the big swings.

[Jasper Gilder]

11 usually - about 8-9 with aircon on. Check that with aircon revs aren't dropping too much. I used to get the warning but a slight retune at service fixed it

[Don1]

DonkeyApple said:

Yup. My 3.6 would dip to 4.

Pressure is really low on idle. It's not great as a design but it is normal for these engines.

I believe the ones with the reworked oil ways have better pressure.

Mine on the new 4L engine never goes below 40 at idle now and is very constant when in use without the big swings.

I'm finding exactly the same.

[TVR_owner]

I'd be concerned that...
a) The car was idling to slowly.
b) The Sensor was reading incorrectly.
c) There was something wrong with the engine.
d) I had the wrong oil in it.

4 psi is not enough and will lead to long term damage unless the cause is b).

b) is most likely, d) is one that will bring an opinion from everyone that thinks they undertsand oil grades, but possibly dont.

[Zippee]

I agree with above - 4psi is too low.
I had similar on my T350 4 years ago and the cause was a worn bottom end bearing causing the low pressure - remedy a bottom end rebuild (fortunately under warranty from initial purchase of the car) so please get it checked out. It may well turn out to just be a sensor but play safe.

[Englishman]

Zippee said:

I agree with above - 4psi is too low.
I had similar on my T350 4 years ago and the cause was a worn bottom end bearing causing the low pressure - remedy a bottom end rebuild (fortunately under warranty from initial purchase of the car) so please get it checked out. It may well turn out to just be a sensor but play safe.

What is your engine rpm and oil pressure at really hot idle now? Thanks!

[Zippee]

After the bottom end rebuild hot idle was 16psi at 850rpm.

[Englishman]

Interesting. Guessing idle without load would be about 1000rpm then for you? Not sure what the recommended idle rpm is, but my dealer sets it to ~850rpm which means with ACU and cooling fans on it can drop to 650/700 rpm.

Without wishing to start another debate on oil, just for the record what is everyone else using? Mine has Shell Helix Ultra 5W40.

Edited by Englishman on Thursday 26th July 09:59

[Targarama]

I'd change the oil pressure sender before panicing too much. But don't leave it for long.

[Zippee]

Englishman said:

Interesting. Guessing idle without load would be about 1000rpm then for you? Not sure what the recommended idle rpm is, but my dealer sets it to ~850rpm which means with ACU and cooling fans on it can drop to 650/700 rpm.

Without wishing to start another debate on oil, just for the record what is everyone else using? Mine has Shell Helix Ultra 5W40.

Edited by Englishman on Thursday 26th July 09:59

I was using Shell Helix 10/40

[Cockey]

I've been told not to be overly concerned at low figures at high temp as the sensor is not very accurate at low pressures.

[TVR_owner]

Cockey said:

I've been told not to be overly concerned at low figures at high temp as the sensor is not very accurate at low pressures.

Sensors have been known to be a tad fragile. In 8 years and 7 S6 engined cars, we have had to change 1, so they aren't "that" bad.

I would be concerned enough to either change it or at least have a master gauge on the engine to check the actual pressure.

Suspect the person that advised not to be overly concerned at the low figs at high temps would not be overly concerned if you finished up with a 10K bill for a premature rebuild?

[Cockey]

TVR_owner said:

Cockey said:

I've been told not to be overly concerned at low figures at high temp as the sensor is not very accurate at low pressures.

Sensors have been known to be a tad fragile. In 8 years and 7 S6 engined cars, we have had to change 1, so they aren't "that" bad.

I would be concerned enough to either change it or at least have a master gauge on the engine to check the actual pressure.

Suspect the person that advised not to be overly concerned at the low figs at high temps would not be overly concerned if you finished up with a 10K bill for a premature rebuild?

You could be right

[Englishman]

As you do with TVR's been gathering evidence....

Connected up the laptop tonight and oil pressure indicated on the S6 diagnostics is about 10psi while on the dash it shows 5 or 6psi. Does anyone know if the two displays are fed from different sensors?

[Legacywr]

Mine is running 8psi when hot, I spoke to boostedcerb last night who thinks the pressure sensor is located in the ideal position, so isn't getting a true reading!?

[alex_gray255]

Install a real time engine monitoring system which feeds the info up through to a 7 inch SatNav display if you have one or a portable reader.

Then you can ignore the dash display and read the real thing.

[astonman]

Try using castrol 10/60 synthetic, I have never seen below 24psi on idle even when oil 88 degrees plus.
When ever ian at torque rvt sees the pressure he always comments on how high it is!
Simon.