MG Car Repair: 77 MG Midget High oil pressure, oil pressure gauge, pressure relief valve

Question
Howard,

Thank you for your previous help with my brake problem. Turned out the piston in the new master cylinder was sticking. All is well now.

I have 250 miles on a professionally rebuilt engine. The oil pressure was consistent at 40-50 psi. This week start-up pressure rose day by day to 70-80 psi The mornings are quite warm here in the south USA.

Warmed-up pressure generally drops to about 60 psi. Slow idle drops drastically to 20-30 psi. And there is evidence of oil dripping from the pressure relief valve when parked.

FYI The dual water temp. and oil pressure gauge was also professionally rebuilt, but I suspect there may be a problem with the water temp also - it reads quite low. Possibly a faulty gauge is adding to the confusion.

Following your 'one thing at a time' approach, how do you suggest I proceed?

Thanks for you help.
Conrad  

Answer
Hi Conrad,
First I would get a known good hydraulic oil pressure gauge, even if you had to purchase a new gauge and keep it as a test tool. This will confirm the gauge reading. A slow idle of 20 to 30 PSI and a cruise speed of 60 PSI is fine. Some times a cold oil and a start up may have a sticky pressure relief valve and show a high reading. That is not uncommon. The oil pump is capable of 300 to 400 PSI if the pressure relief valve were to stick closed.
Don't gauge the pressure with cold oil, warm the engine oil up first (which takes longer than the coolant temp) Then test the pressure. A 1000 RPM idle should show you 25+ PSI and a 2500 RPM should show you 45 to 80 PSI depending on grade of oil and how tight the engine builder set the bearing up at.
Checking with a second gauge will tell you of any gauge problem.
If you suspect a relief valve problem the piston and the spring are available from several suppliers.
Howard