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Q & A: Low Oil Pressure

As a relatively new owner of a 1957 MGA 1500, I’ve found some conflicting information on the subject of oil pressure and was hoping you could help clarify it. It seems that most people I’ve spoken with have recently rebuilt engines so they aren’t necessarily a realistic reference for one that’s got a lot of years behind it. While I’m sure it’s inevitable that I will need to have it rebuilt, I would like to drive the car for at least this season, if possible, if for no other reason than to recharge my enthusiasm after far too many surprises while trying to make the car reasonably roadworthy (but still not much to look at).

I am using Castrol GTX 20W/50 oil with a Fram filter (Moss spin-on conversion). My dual gauge is new, which I hope means it is reasonably accurate. On startup, the oil pressure is around 65 psi. The oil pressure stays reasonably high for some time after the coolant temperature has reached a normal level (180 deg. thermostat), but by the time I’ve run it for maybe a half hour, it is down to around 20 psi or slightly below at 1000 rpm idle and at 40 psi or slightly below at 2500 rpm. I haven’t had it out in temperatures above about 70 deg. so far, so I’m imagining things getting worse as summer gets here. I’m not sure at what point the alarm bells should be going off in my head though. In the original workshop manual, they say the oil pressure should not be less than 10 psi at idle and it should not be below 30 psi at “road speed”. Most of the comments I’ve seen on the internet seem to suggest it should never be lower than 50 psi at 3000 rpm, however, so I don’t know who to listen to.

I’ve had some people tell me it should be fine for a few thousand more miles and some suggestions that adding an oil cooler would help. I’m planning to make a 600 mile round-trip in July to attend GT-33, my first NAMGAR event, but I may reconsider driving it if there’s an imminent catastrophic failure of some kind. Even though roadside breakdowns make for some great fireside stories, I’d rather avoid them and be a boring conversationalist.

Your bearings are bad. Do not drive your car until they get changed. You need to change the 4 rods, center main, and oil pump. All of which can be done from under the car. There is no substitute to calling the shop for help. John has his technic... read more