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MG MGB Technical - another oil pressure question

All this talk of oil changes and pressures i think has started something on my car...

The BGT has suddenly developed a loss of oil pressure when starting from cold...

The oil pressure used to crank up to 60psi from cold with full choke instantaneously as soon as the engine fired. When warm, idle was 20psi and driving when warm was a rock steady 60psi.

The last three startups from cold have resulted in 0psi. On crank-over the pressure rises to 60psi, the car starts and immediately the pressure drops. The pressure needle attempts to rise several times during idle but then falling again. This happens until nearing normal temp and then the pressure picks up as normal. pressures are as described at the top when warm.

Normally as the oil pressure is always fine i try to drive off asap after starting to let the fluids move around the engine thus warming it up quicker, however it shocked me so much to see the pressure falter on a normally fine engine ive let it idle to normal temp giving the chance for the pressure to build....

The car does not burn oil as a rule, howver it is due for an oil change this week, but as we'e been talking oil a lot recently i thought i might ask the question and should i be looking for anything more serious.

The oil is rather black and opaque, quite alarmingly so actually; it is exactly 3000miles since last change and my oil pressure gauge was replaced at this interval due to a snapped temp sender. I dont suspect the gauge as it reads similar to the old one once the car is warmed up. I do not ever recall the pressure dying like this when due for a change before...

Is it a case of sediment in the pump causing probs or more serious?? Oil currently 20W/50. Assistance apreciated chaps


~PHIL
Phil

Phil,

Have you checked the oil pressure relief valve...it's on the lower left hand side of block....don't know if it could cause the pressure to go to "0" or not. When operating normally it is supposed to limit oil pressure to 85 psi I think. If pressure exceeds that, then the valve opens and bypasses.

Also, could there be the possibility that there is some small restriction in the line to the gauge that's expanding when hot?

Doug
Douglas Keene

This thread was discussed between 16/10/2002 and 18/10/2002

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