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MG MGB GT V8 Factory Originals Technical - V8 Oil Pressure

The engine of my MGBV8 (Rover P6 unit) was professionally rebuilt about 8000 miles ago. The car has been looked after since by two careful owners, who each sold the car for genuine reasons.

The engine pulls beautifully and is running on all cylinders. The car is quite a lot quicker than my other (1950cc stage 2)MGBGT.

There is no oil smoke from the exhaust. The engine uses very little oil, even during sustained high speed cruising. The oil keeps its colour and consistency between changes, i.e. stays brown. Oil level is maintained at the max setting on the (original) dipstick.

There is no evidence of debris of any kind in the oil at oil change time.

Temperatures stay good. The Kenlowe fan only needs to cut in if caught in stationary or slow moving traffic for a while. Otherwise, the (added) oil temperature guage shows 65-80 degrees and the water temp guage stays moderate.

Engine noise is minimal. In particular, the tappets are quiet (as in you can't hear them except for a couple of seconds at startup).

The oil pressure guage is rock steady, from idle right up to 2500 RPM. Sustained cruising above that speed raises it a little.

However, the indicated pressure on the standard MGBGT guage is only about 22 PSI up to 2500 RPM. I've read that pressure should be 30-40 PSI on a warm engine at 2400RPM.

Should I worry?
Do the oil pumps wear?
Could the sensor be at fault?
There used to be a kit to uprate the oil pump output. Is it worth doing this?
Any other ideas?

Comments appreciated.

Chris Ward

Hi Chris,

I've got a factory BGT V8 and live in London so tend to spend a lot of time sitting in traffic. So I had the same concerns as you a couple of years ago. The Old V8s as fitted to the P6 and MGBGT V8 have a gear pump wich is about 1/2 the size of the later versions. I suspect that this is why the factory V8 has an idle speed specified of 800rpm, the engine is quite happy to idle at 500 but the extra revs keep the oil pressure up. I had to replace the cam a couple of years ago and so I fitted the Hi-flow gear pump kit you mention (from it was an easy swap once the engine front cover was off and I didn't need to take the engine out of the car to do it. Afterwards peak oil pressure was the same as before (pressure relief valve opening) but idle pressure was improved 50%to about 25lbs. Having said all the above 22lbs at idle sounds fine to me. My engine was getting down to 10-15lbs, on the other hand it did chew a couple of lobes off the camshaft (common at 95k miles - see FAQ's on the rpi-engineering website). If you do do the swap then a couple of good tips are to bed the pressure relief valve piston into place with grinding paste and, once it's all installed, prime the pump using a srewdriver shaft in an electric drill.

Best regards

Philip Shingler

Trouble is, Chris says he is only getting 22psi at 2400 rpm, a lot higher than idle, and that is low. But then he also implies that it hardly alters at all from idle right up to high-speed cruising. I would begin to doubt the oil gauge (there is no sensor as such as an electrically operated gauge would have) and connect up another gauge to check.

My V8 idles at around 20 when hot, although it will drop to 15 with sustained idling, lower still on very hot days, which is when I resort to fast-idle to keep the pressure up a bit. From 2000 rpm or so up it reads a shade under 40.

Roger Parker has said in the past in relation to Police V8s "What oil pressure?" when hot. The manuals also describe the V8 oil sytem as 'high flow, not high pressure'.

There were also three different gauges used in the relatively short build-life of the car - originally 60psi, then 100psi from Sep 74, and 80psi from an unspecified date to the end of production.

Paul Hunt

This thread was discussed on 03/12/1999

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