My 1969 Mini 1275 usually shows 75-80 on the Oil Pressure gauge when I'm at the high revs. The other day I drove it on the freeway at 55-60 mph for 30 minutes and the oil pressure dropped way down to 20 or so. The temp gauge was showing under the Red, but close to it. After leaving it parked for a couple of hours it seems to be back to normal. Is this simply due to the oil getting too hot, and thin? Anything to worry about?
Ed. in L.A.

 

There are many things to consider. I personally would look into why your running a bit on the warmer side. Ive always ran a cooler thermostat. What temp are you currently running? On older cars in general they seem to perform there best with the coolest anyways. Hotter running engines do tend to drop in oil pressure.

 

It was running at and into the red until the radiator was flushed. It tends to run in the mid-range when the weather is cool (for So. Cal.) and only gets way up there on hot days when I'm on the freeway for awhile. I am concerned about the oil pressure drop since it never did that before, and I was wondering if any problem might be developing.

 

Personally if your living in a warmer climate like So.Cal I would be running 160 degree thermostat or the coldest possible.. But onto your oil pressure thing it could be several things. Currently what type of oil are you running in this classic gem? I would keep an eye on this because of you drastic swing in pressure. Another thing you could also do is change out your oil sending unit. That could be getting weak.

 

The thermostat only regulates the flow of coolant while the liquid is cold. The degree of the thermostat determines when it opens and allows the coolant to move through the radiator. Unless the current thermostat is stuck closed, a new thermostat would do nothing to help reduce the running temperature of your mini. (And thermostats usually fail in the open position)

An easy way to check a thermostat is to pull it out of the car and throw it into a pot of water on the stove. It should open as the water boils.

How a thermostat works

I had a similar problem with oil pressure in my 1275 A+. It would take longer than normal to build pressure at startup, but would be fine while running. After the motor was at temp the pressure would drop. It would get down real low at idle ~10 (but only when the engine was warm). It turned out my oil pump was going and I had to replace it.

For low oil pressure I'd check these in order:
1) Correct oil type. The A-series oil slump is shared between the engine and the transmission and requires a heavier oil. 20w-50. There are plenty of threads on the best oil to run in a classic mini. You can use the search and read through them but I run Valvoline VR1 20w-50 because it has high levels of ZDDP.
2) The oil pressure relief valve tends to scar and stick. They're cheap and easy to replace. I'd replace the spring at the same time just because they're also cheap. A replacement on minimania
3) Last to look at is the oil pump. Most expensive option here and would be the last resort.

Good Luck