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Since changing the oil in my newly bought MG Midget 1275, the oil pressure goes
down to about 10-15 at warm idle. There is no excess smoke from the exhast, and I don't think
it is the oil pump or the instrument.
I used normal 20/50, but I spoke to my local MG garage who told me that oil pressure should be
at about 40-50 on tickover and 60 at 3000 rpm. Can anyone clarify that? Particulary as they
told me that I need a new engine now and its dangerous to drive it.
Any other ideas?
Answers:
60 at 3000 rpm is what my 1500 runs at. When the engine is cold it runs about 70 at 3000 and when it's warm, (after an hour or so) it may be as low as 50 but tends to average at 60. I have a high performance cam in mine so the idle is set high (1000-1500 rpm) to keep it from stalling at stop lights and smooth out the lumps. The pressure still runs about 40 at idle. I'm using 20W50 oil as well.
My 948 mark II Sprite used to do the same thing and I drove it that way for quite some time. The problem was the relief spring was getting old and lost tension when hot, allowing the oil pressure to drop. A new relief valve spring corrected the problem. If it does not, then you will have to, at some point, rebuild the engine. Wear on the rod and main bearings will also lead to a drop in oil pressure as the engine warms up. Since the spring is the easiest and cheapest part to replace, I would start there. If you are not hearing any rod nock, etc. I would not be unduely concerned at this time.
If your engine does 40-50 PSI on idle when hot, I think you
should keep it as an exhibit. (Or maybe your idle speed is
2,500 rpm?!) I think you answered your own question.
Wnen hot - and this means after 30 mins plus use, when the *oil*
is hot:
10 psi on idle is OK
20 psi on idle is fine
50 psi or more at (say) 3,000 is OK.
When the engine's warm, any and all of these numbers could be
60-80.