VCCA Home Forums TECHNICAL - 1945 AND NEWER 1946-1948 Oil Pressure

The oil pressure gauge in my '48 Fleetmaster (216 six) reads "0" most of the time it's running unless I'm accelerating in 1st gear, and then it moves close to 15 but moves back down when cruising. Is this normal for these engines? I have to remove the cluster to have the "gasoline" and "battery" gauges repaired as they are totally inoperable, and need to know if I should also have the repair place look at the oil pressure gauge as well. This car runs very well, no obvious lubrication issues other than some small leaks.

Do you have 10w30 oil in it? Is the oil fairly new?

It sounds a bit low for a 48 and I'd be tempted to connect another gauge to the block just to see whether it's a gauge problem or an actual pressure problem.

The correct oil pressue would be 14 pounds at 50 MPH.....about 10 pounds at 30 MPH and 8 pounds at idle. (with hot oil) . The oil pump screen may be plugged.
I would suspect the by-pass valve in the oil pump is stuck open.The dash unit very seldom has a problem. Continued operation can ruin your engine.

Wow! I am using a multi-weight oil. I have a mechanical gauge I'll hook up to do a test. I've been driving this car since I got it in 2015 with no issues, but really not at any great distances. If the test gauge nets me the same results as the in-car gauge, I guess I'm pulling the oil pan. Thanks to all!

The by-pass valve is on the left side of the engine block near the exhaust manifold outlet. So this is not work you do just after running the engine!

If your test shows that the oil pressure is low I suggest you check the valve first. You do not have to remove the pan to do that. If the valve is working correctly then you probably do need to drop the pan and check out the oil pump.

The by pass valve that can stick is built into the oil pump. Its function is to limit oilpressure with cold oil.Usually is set to open at 80 pounds of oi pressure. The pessure regulator valve (in the block in 1948) regulates low pressure to the rocker armsand oil pipes in theoil pan and I would not monkey with that.
The by pass valve in the pump is a ball and spring up through 1939 and a sliding spring loaded valve from 1940 and up. Thev sliding valve can stick with varnish.

So, just to be clear here, if my gauge test shows no or little oil pressure, I should drop the pan and check the screen and the bypass valve. I looked at my parts manual (1929-1954) and on page 133 there is a beautiful exploded view of the oil pump. Looks like the valve and spring are in the cover. Am I seeing this correctly? Thanks for all your help! Also, just as seperate question, can a 12V fuel gauge work in a 6V system? I have my doubts but just thought I'd ask...

Yes, you are seeing ot correctly. It is very important to have the cover gasket the correct thickness of .012" also.

Good idea to clean the oil pump screen and pan also. Hold a graden hose against the main oil pipe in the pan to make sure no oil trough lines are plugged up.
Make 4 1/4" studs (by cutting off bolts) and screw into the pan bolt holes in the block. this will helpto keep the gaskets in place. The side pan gaskets are installed first. I use grease to holld them in place and the end corks last.

OK, I plumbed in my new oil pressure gauge, and got the exact pressures Gene described above. That made me very happy indeed! So now I will remove the entire cluster and send it out for repair. Really doesn't look like any of the four gauges are working properly! Thanks again for all your help and guidance.

I would try to find a NOS gauge. Fits 1942-1948.

Maybe see if you can get compressed air through the tube once you disconnect the gauge at the cluster. Could be some crap plugging it.

I agree with Tim’s recommendation before I would replace the gauge.

Disconnect the thin steel line at both the gauge end and where it connects on the engine. Then blow air from under the dash out to the engine. Put a rag over the engine end.

You might be surprised what comes out.

I expect that the threaded port on the engine is clear because you got good readings with the separate gauge.

I apologize for my confusion on the 2 valves. I forgot that the regulator valve was downstream from where the pressure gauge gets it’s reading.

You probably should start a second thread about the 12v fuel gauge in a 6 volt system. You get get a better response.