VCCA Home Forums TECHNICAL - 1945 AND NEWER 1949-1954 Oil Pressure Concerns

Hello All,
I've been experiencing a drop in oil pressure - particularly after a run at highway speeds. The engine is a '54 235 with hydraulic lifters on its third 10/40 oil change since I fully rebuilt it 12 month ago. Under normal driving conditions where the engine is unstressed the oil pressure gauge easily reaches 30+psi and idles at 12psi. After a short 60-70mph run however, where things get a little hotter, the pressure drops to 20psi when I settle down to a 45-50mph cruise and reaches no more than 7-8psi at idle. It will then only reach 25-30psi when I nail it.
So, my simple question is under these conditions should my Powerglide spec 235 oil pressure be higher than this or is this normal?
Thanks in advance for any guidance I may receive.

My 1951 Chevrolet with a 216 has about the same oil pressure as you describe. However, with a 235 full oil pressure system your oil pressure should be more. When the engine was rebuilt 12 months ago, was a new oil pump installed or did they reinstall the used oil pump?

Thanks for the response Junkyard Dog. Thing is, unlike the 216 the '54 235 Powerglide spec engine has a full pressure oil feed system so shouldn't it be making more pressure?

With the full pressure oiling in a 1953 PG and all 1954's your oil pressure should be around 40 pounds at 50 MPH with hot 10W-30 oil. Idle would be about 15 pounds.
I would suspect a problem with the oil pump or the pump relief valve.

Gotcha. Pressure relief valve spring too weak perhaps?

Or valve sticking.
What is the history of the oil pump?

Fully rebuilt with a new spring and the valve and bore were both in good shape. I'm going to take it out tomorrow however and see what's going on.

The cover gasket on the oil pump must be of the correct thickness. A new gasket should measure about .009". If too thick pressure will be low.

Today's news - I checked the pump over and all seemed well. I didn't peel off the new felpro cover gasket to measure it, replacement stovebolt parts are not easy to come by in the UK. However, I did perform an experiment; suspecting a weak spring I milled up a 3/8in shim and slid it into the relief valve piston to pre-load the spring. This has made no difference whatsoever. Please correct me if I'm barking up the wrong tree here (not for the first time...) but my best guess is that the pump has been rebuilt previously with too weak a spring (a lot of mend and make-do goes on over here). This could be making the valve cave in at the slightest hint of pressure irrespective of any pre-load I might throw at it.
Given I have a 600+ mile journey to make in a few weeks I'm going to have a new one shipped over. Anybody know where I can get hold of one?
Thanks, T

I would recommend replacing the pump. New pumps are available from www.fillingstation.com...their #RW-715 for $99.50 in my 2014 catalog.
The pump fits only 1953 Power Glides and all 1954 engines.

My futile search for a spring has led me to the same conclusion. Thanks your your help.
T

National Chevy in Minneapolis Minn. Specialize in early 50s Chevrolet.. Great help in my rebuilding my 54 wagon

The spring shows in my parts book to be 1-3/16" long. Might be good to measure yours to verify that is the problem.

For the work involved I would replace the pump and cover all bases.

I concur that there is a problem in the pump.

Regardless of the spring in the relief valve you should have observed a pressure increase when you shimmed it if the pump was working correctly. The fact that there was no pressure increase indicates that the pump is bypassing oil internally and cannot build more pressure. In effect it is its own "relief" valve.

There are 3 areas where oil will bypass.
1) Between the gear teeth.
2) Between the OD of the gears and the bores in the pump housing.
3) Between the upper and lower faces of the gears and the housing and end plate. The end plate is the area where oil bypasses when the gasket is too thick. This often happens when someone grabs the nearest sheet of gasket material and makes that gasket as a make shift. Gene's advice about that gasket is right on target as always.

I too have a 51 216,andam experiencing the same low oil pressure after highway speeds as Junkyard Dog in his 51. Is this normal?

The oil preddure should be about 14 pounds, hot oil , at 50 MPH. At idle about 7 pounds hot.
What is your pressure?

He told me that his oil pressure is 7 to 8 pounds hot at idle, which is the same as my '51 Chevrolet.

Just asking ,did you try another oil gauge?

He mentioned that his oil pressure is 7 or 8 pounds at idle when hot. That is normal so his oil pressure gauge seems to be functioning correctly.

Just asking, did you try another oil gauge? also wondering if you get any valve clicking with that low oil pressure when its hot at idle?

What is considered too low oil pressure range using 10w-40 oil in a 54 235?

If it is below the range then I think I would replace the pump if all other inspections indicate that it is the culprit.

If in in within the range, then I would leave it alone until it gets out of range or blows up whichever comes first.

I think Chevys of the 40s also carries oil pumps. And one can use the chat parts wanted site. Gene probably has one.

Best,

Charlie