VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1937-1945 oil pressure 1939 chev

does any body have a chart or know what pressuers we should get at different rpms on the 39 engine thanks tony

Tony,

I've never seen such a chart. It would be interesting to see one.

Anyway, absent such a chart, the best I would guess is:

Cold Peg the needle (30 lbs plus)

Warming up: Slowly decreasing to 20 lbs

Fully warm (170-180 degrees and no cooling issues and moving: 18-19 lbs

Idling: 8-10 lbs

All above are approximate and based on a 41 216.

My dad once told me that on these old engines, when the pressure starts increasing from the norm it may be an indication that the tubes in the pan may be be getting stopped up. Don't know about that.

Best,
Charlie

The factory says 13 pounds at 2600 RPM. This would be with hot #20 oil. The maximum blow-off pressure is 75 pounds.
At idle the 1937-1939 will show only about 3 pounds with hot oil. This was improved in 1940 with the larger gears. The pressure at idle was more than doubled.
My '39 with the original pump matches these pressures.

That's an interesting question. A gear pump pumps volume versus rpm so the curve should follow the overall pressure drop in the oil distribution network. That network could create an almost straight line pressure curve versus rpm (if the network has little restriction for all flow volumes) or it could rise significantly at higher rpms (if the network is restrictive). The variable is the oil distributor spring, is it considered the relief valve that only opens at 75 psi? What is the highest pressure you have seen in your 39 and at what rpm?

Brian

Just some info. from various Chevrolet material.
The 1937 was the first year for a gear type pump..Chevrolet said the advantages of the gear type pump was "the action of the whirling gears was the same as as the two tooth (vane) vane type pump. The vane pump delivers two slugs of oil per reveloution where as the gear type delivers seven due to the seven gear teeth.This makes the oil flow continuous rather than surging. The smoother oil flow creats greater pressure at higher speeds."
The blow-off valve for 1937-1939 is a spring loaded ball in the pump. It prevents the pressure from exceeding 75 pounds when the oil is cold which could cause breakage and leaks.
It is mentioned that the oil pressure gauge reading at lower speeds will vary little from the 1936 (vane pump). However at over 20 MPH the gauge will show a higher pressure passing 18.5 pounds at 70 MPH with a warm engine.
The reason for the higher pressure at lower speed (above 20 MPH) was to get the trough oil pipes to squirt oil directly into the dippers sooner. For 1940 the low speed pressure was increased by the larger oil pump gears for that reason. (the 1940 and up oil pump had a sliding spring loaded valve for relife rather then a ball and set at 60 pounds)
All of the engines/gauges will peg the gauge at 30 pounds with cold oil.
I have never experimented with a higher reading gauge to see what the actual pressure was.
The oil distributor valve merely splits the oil pressure, sending the high pressure to the main bearing gallery and the low pressure to the points with open ended tubes such as the trough oil pipes and rocker arms. In 1939 they revised the rocker arm oiling sending the rocker arm oil from the high pressure side but restricting the flow to prevent over oiling. They said this was done to get oil flow to the rockers faster - to make less valve train noise.
At top speed with hot oil My '39 reads about midway between 15 and 30 pound marks. That would be at the 4000 RPM range.

Thanks Gene, that makes sense, the distributor spring must act as a simple pressure controller that keeps the pressure higher at low rpm and flattens the curve slightly at higher rpms. That would put the hot idle pressure at between 2 and 5 psi if the spring has a constant "k". The spring would also generate a higher pressure when cold which would put more oil in the right places before the engine warms up.

Brian

hi i counldnt tell you the rpms as i dont have a tacho but at idle the gauges just off the low stop on gauge more or less zero it might be reading a wee bit at 30 mph with a 3.7 diff i get about 5 to 7 psi it dosent seem to be revving much i will have to have a look at a faster speed i only just got it going again with the 3.7 diff and some motor work was done i was hoping for more when cold the gauge is maxed out to the stop so the pump is pumping

The 6th edition of the Motors Factory Shop Manual has this in the Chevrolet chapter:

hi my oil pressure might be about right for the speed im doing i will go for a faster ride and check i could fit a rpm gauge as well what would be the max rpm you would go to out of interest

I get 14 pounds on the open road...If you do get an RPM gauge let us know what your max is...er, was...Check the speedo while your there...Sounds interesting, cheers.