With 10w-30 oil, I am seeing hot pressure at idle somewhere under 10psi and at 2000 rpm around 30-35psi. Thinking these numbers indicative of loose bearing clearances, I switched to 15w-40 (after rebuilding the gerotor pump, which made no difference). With the heavier oil I picked up about 5 psi at both idle and 2000 rpm.

Would it be prudent to move up to 20w-50, stick with 15w-40, or revert to 10w-30? This is a stock-style street-driven engine.

1954 Crestline Victoria 312 4-bbl, 3-speed overdrive

10/30, however why don't you put in a set of bearings?

I don't see any harm going up to a 20-50.  Been running that in a 302 for years summer or winter..  A 10-40  should be good to use too.


54 Victoria 312;  48 Ford Conv 302, 56 Bird 312
Forever Ford
Midland Park, NJ

who rebuilt the greater oil pump.if the alum jeroter has ware of the housing a newer and inner steal rotor will do nothing. with my 292 all new bearingscam bearings etc 1040 oil gives 25 pounds at idle,40 at2500 hot.. my issue with jeroter is content drips at mount gasket. the issue is over torque  trying to stop drips warp housing. have purchased a gear pump with cast iron body. haven't installed yet. will shortly. just my takeongeroter pumps

You could try shimming the oil pump pressure relief spring with a few small washers and see if that helps.



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Are you sure your gauge is accurate?



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Excellent point on checking the accuracy of the gauge.

The hot oil pressure specification in the 1957 service manual is 45-50 psi at 2000 rpm.  You do not mention how many miles are on this engine so if it’s relatively low mileage since it was last worked on, then it might be worth revisiting the oil pump.  I have found that the end play or bottom clearance on either style of pump is critical.

Here are the specifications for both the spur gear and gerotor (rotor) oil pumps when rebuilding them.  Per the manual, the oil pump to cover plate torques to 12-15 lbs/ft.
  

Lorena, Texas (South of Waco)

I do not know the engine’s history. I have had it for less than a year, it is not original to the car, and I am sure that the previous owner did not rebuild it. My best guess would be that it was removed from a 1956 Thunderbird to replace the car’s original engine sometime in the 80s-ish.

The pressure gauge is new, but of course that doesn’t guarantee accuracy. I installed it because my oil light was flickering on at hot idle with the 10w30.

I installed the rebuild kit in the gerotor pump. I checked clearances per a shop manual (I think I used the one from 1959) and resurfaced the steel plate. Everything checked out ok as I recall. The old rotor had some pitting at the rotor tips.

I don’t plan to overhaul the engine anytime soon, so I’m just trying to determine what oil will give the engine the best longevity as-is, until a potential future rebuild.

Presumably if observed pressure is lower than spec, the volume of oil reaching the end of the line (rocker shafts, correct?) will be reduced at a given engine speed because of internal leakage. More viscous oil may not leak internally quite as much, thus somewhat increasing the volume to the later parts of the oiling system and also the pressure at the gauge. I do not know how important the actual pressure or film thickness of the oil at the bearings is. I am sure that oil is getting everywhere in the engine, even with 10w30, but not whether increasing viscosity will actually reduce internal wear relative to a lower viscosity.


1954 Crestline Victoria 312 4-bbl, 3-speed overdrive

There is only wear if there is no oil. With the engine warm after running and you can easily remove the rocker arm covers, take one off and start the engine to see if oil comes out the overflow. I use a cardboard defector and there is very little splash. If there is oil on both sides I would not worry at all as all the passages are oiled and there is enough pressure to get oil to the rocker system.
 10 psi at idle and 30 when running is fine for most engines in light use.
 There are some brands of oil with lower pressure. Pennzoil always did that from my experience. 

56 Vic, B'Ville 200 MPH Club Member, So Cal.

block off rocker spill tubes, if you have a good flow ther is no need for the loss of oil flowing fact better lube to all rockers improve camshaft life,as well the oil leaking from rocker shafts get to front  and rear holes,if no leaks at all rockers rockers  farther from spill tubes are probably plugged with sludge.