Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing Oil Pressure Gauge

I have a 1971 4/4 Competition, Kent engine (not sure if still original). Car runs very well and oil pressure is OK but:

On Start up pressure is immediate, no lag and is steady somewhere short of 50 PSI when warm and running.
What concerns me is that gauge show little or no change when idling and when engine is turned off pressure drop is not immediate, sometimes talking several minutes to drop off and then in two stages.

I thought that gauge maybe defect and had it tested when in the UK last September (i live in Austria). Gauge was returned as checked and in order. I temporarily installed a standard Smiths circular gauge but got the same behaviour.

I have had several suggestions from friends and VDO (Instrument supplier in Austria):

1) Bleed off any old oil in line between Block and Gauge - done, no change
2) Increase bore of pipe between block and gauge even though constriction at gauge will be the same as now. Yet to try this one.
3) High oil pressure relief valve not working. (Indicated pressure does not exceed 50psi regardless of rpm!) Not sure about taking this on myself.

Oil pressure as such does not seem to be an issue but since we have some long trips coming up it would be good to have more faith in the gauge reading.

Anybody with similar experience?

Oil was changed maybe 5000km ago and is currently a mineral 20/50 a bit heavier than that used before. Could the heavier oil impact on this?

I've also thought about installing an oil pressure warning light in parallel with the gauge. This I might do if I try the second option above. If I do what rating should the oil pressure switch be, 15psi?

I welcome any comments!
Many thanks

Martin

Assume given age of car and comments you have a mechanical gauge rather than electric one. If so there will be some air in the pressure line to gauge or gauge itself. Not an issue as any air will simply compress and exert same hydraulic pressure on instrument tube. It may have a damping effect on pressure indication particularly during startup and shutdown though.

The fact that 50 psi is maintained irrespective of revs suggests PRV is working.

As Martin is one of a small group of owners of older Kent engined 4/4s here I have talked to him about the problem and driven the car a number of times. My guess is that Richard is correct in that something is having a damping effect on the gauge and that could very well be air in the line. Line diameter could also have an effect but seems less likely.

My car, same engine and smiths gauge, reacts differently e.g. 15 psi at idle when hot and max oil pressure 36 psi when hot and running at cruise power. I think this is close to normal.

Just to put the question slightly differently: should Martin continue to pursue the issue of consistently high oil pressure regardless of engine revs? Has anyone experienced a similar issue?

Plus 8 owners should see similar pressure drop at idle in a warm engine as the Rover V8 does this. Alarming when first seen but apparently normal.

Thanks Richard,

yes gauge is mechanical and your comment re PRV make sense.

When it gets a bit warmer here I think I'll change the oil to a lighter grade next and make sure the line is well bled.

It's possible you have a high pressure oil pump which is starting to get tired. These pumps were very common on crossflow rally cars.

The high pressure oil pump should run around 65psi running speed and still be around 15-20psi at idle. 20w50 is an appropriate grade of oil. Check for any restricitions in the oil line between the block and the one-shot and the one-shot and the gauge. Air in the line will present as the gauge being slow to react when the car is first turned on (it'll look like no oil pressure for a second until the air is compressed or pushed out). If everything looks good, I'd probably change the oil again and forget about it. If you're really worried about it, put on a new oil pump. Their not too expensive and are easy to install.

Thanks Ray, will change oil and clean line to block. One-shot has been removed from my car.Thanks again