1946 Flathead Low Oil Pressure

[wicho46]

Seeking advice from fellow Cadillac members.
When engine is Cold 30psi is pressent at gauge, once engine warms up to temp my oil pressure falls to 8psi. AT IDLE. 
When engine is at 2800rpm the oil gauge only goes up to about 11psi. when engine is at running temp. I cant seem to figure this out.
When running cold 30psi present but gauge starts to drop down to 11psi even though car is running at about 45mph. Running straight 30w non-dtergent oil since I have NO aftermarket oil filter. I will drop the oil pan and inspect the oil pump.
I have a spare oil pump I came accross, but those gears inside are cut straight. VS the original's that were cut at an angle. anything I should look out for? What should I check for? Would the other gears work? I'll take any advice. Thanks.
Thank You
L Lopez

[Fred Pennington 25635]

If you are using the dash gauge, I would verify the readings with another gauge before tearing into the engine.
Low oil pressure is more indicative of worn bearings, but the pump can also be the problem. It is easier to repair and might give you some time before you have to do the bearings. The main issues with the pump is wear or scoring of the bottom plate. Often times you can just smooth out or replace it. That's the shade tree method but it works better than most people would admit too. The pumps and kits are readily available and the job can be done in an afternoon.

One last thought, the pick up screen could be full of sludge, one way or the other you are dropping the pan.

Good Luck
Fred P.

[pauldridge]

Seems to me if the pickup screen were clogged you'd have low pressure at startup as well.

If it were me I'd pull the pan, get some plastigage and check main and rod bearing clearances as well as that pickup screen.

Rig up a remote starter switch to get rod caps at straight down positions. You'll want #1 piston near TDC to remove the pan or that crank throw will prevent the oil pan from clearing the drag link.

If you can get it on a lift the whole job can be done in 3 or 4 hours

[Doug Houston]

Leave the rod caps alone!!

The worn bearings, if there are any, will be the CAMSHAFT bearings, which can't be replaced from the bottom of the engine.

While the oil pan is off, check the regulator plug in the oil pump, and if it's stuck. That will make the oil pressure behave as described. If new oil pump gears are to be had, buy new ones, and a new regulator valve.

If this doesn't bring oil pressure back to normal the cam bearings are probably gone.  That would signal a rebuild. (and NOT a Chevy small block replacement!!)

And also no 12 Volt conversion, either.

[Glen]

This maybe totally off the wall but…. Some diesel engines I work with have low oil pressure when the oil is worn out.  I watched the oil pressure and if it went low at idle when at operation temperature I knew it was time to change the oil.  Fresh oil always brought the oil pressure back up. 

It cheaper to change the oil than any other option.   

[gary griffin]

  I know oil gets dirty but does it wear out? Is it possible that it gets contaminated by fuel from the combustion chambers?  I know diluted oil is likely to have less oil pressure. I went to a Navy diesel mechanics school when I was in the army reserves (1959) and I seem to recall that as engines wear there is more blow by and thinner oil would show up as low oil pressure. My knowledge is limited and not current but also many diesels are 2 stroke and could bypass more fuel than 4 strokes would.

  Diesel evaporates at a lower temperature as Gasoline so gasoline residue would accumulate in the oil contaminating it but not diluting it. 

[wicho46]

I removed the oil pan. Pickup screen was clean. I repaced the oil pump with a spare that I had, the 2 oil gears are cut straight on this one. Put back into engine  and  35psi on this when cold, dropped down to 18psi when hot at idle. Yes when engine is driven I get a good 30psi on gauge.  Looks like problem has been resolved.  Glad to get my daily driver back on the road.
1946 Cadillac 4dr. 61series
L Lopez

[1937 LaSalle coupe]

Hello L Lopez. I have used the product ' STP Oil Treatment ' for over 40 years. I do oil changes at 3000 miles and you can still feel the  slipperiness of the STP at the time you change oil.  This is a good thing if you can prevent friction which prevents heat and that is good for engines. You were right in dropping the oil pan and checking the screen. Glad you had a cheap fix... John Lehman... CLC# 26365...

[Whit Otis, 1188]

Amen on the cam bearings, Doug Houston.

Whit