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MG MGB Technical - Oil pressure

Oil pressure of my '71 MG BGT is always a constant 70 at speed and just above 50 at idle. But yesterday something strange happened. Oil level was okay. Pressure went up to 50, lowered to say 30-40 and than up again to 50, and 40 again. After 5 minutes of driving it slowly went up to 70. But then after a short stop the same happened. So I stopped again for some minutes and then fired her up. Pressure then got to 70 and stayed there. I drove her for a trip of 40 miles without losing pressure, idle value was also correct at 50.

Never had this before...anyone out there who can explain this "behavior"?

Thanks in advance!

Jasper
Jasper L Nederhoed

Could have been a speck of dirt in the non return valve that has now cleared. Just goes to show though that oil pressure gauges are sometimes more nuisance than they are worth because had you got the oil pressure light it wouldn't have illuminated until the pressure had dropped to about 7psi and you wouldn't have known a thing about it and no harm would have been done. Just keep an eye on the gauge for the next few miles.
Iain MacKintosh

Didn't cross my mind but I think you're right. Thanks

Jasper L Nederhoed

Pressure relief valve (on the block), I think you mean, the non-return valve (in the oil filter) will be open all the time the engine is running. But I'm with you on the worry-meter. About the only thing it is good for is indicating a slow reduction in pressures under given circumstances over time. If the pressure suddenly did drop unless you are watching the gauge like a hawk instead of what is going on outside you wouldn't see it for a while anyway. Even a light has its limits, some years ago I watched a hill-climb car roar off the line with a large orange light (a Mini indicator unit) right on top of his dash glowing strongly - yes, it was an oil pressure warning light, his oil filter had fallen off, and he didn't notice for a couple of hundred yards at full throttle.
PaulH Solihull

This thread was discussed on 03/08/2011

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