The Stovebolt Site Forums The Shop Area Engine Shop Oil Pressure Question

Although this isn't GM, we were wondering if any of you experts out there can help us. We have a '47 Diamond T model 509 with a Hercules JXC L-head (flat head) engine. When cold and under load, the oil pressure gauge drops to zero. This is not RPM dependent, as it is fine during idle. If pulling a grade when cold and you let off the gas, the pressure goes back to normal. At all other times, the pressure remains 30-40 lbs., which is optimal. Some have told us that this may be worn bearings. What do you think?

Does it have an electric guage or an actual oil line to the guage?
Is there anything interferring with the wires/oil lines from the sender/fitting to the guage :confused:

Only when cold is the weird part. Are you sure you have the right oil in it?

The pickup screen on the oil pump needs cleaning!
Every couple months if your usin the truck
I bet no one has done this in years on your truck

That sounds like a good chance. But, are you telling us you drop the pan every couple of months?

Change your oil every six months if your not driving it or every 1500 miles

Clean the pickup screen every 6000 miles or twice a year.

Water!!!! will also clog the screen....is the oil
milky?

Clean the pick up screen every 6 months? Geez I am years behind on that on every vehicle I ever owned. I once had a Dodge van, the slant six wouldn't pick up oil pressure when it was cold outside The engine had so much blow by, the excessive condensation would freeze on the oil pick up, which was allready pretty sludged up.It finally cured itself when a rod made an unscheduled exit through the block.It was easy to examine the pick up through the hole.

Thanks for the replies, but please read our question carefully. The oil pressure is fine at idle, but drops when pulling a grade at an RPM that is higher than idle. This does this only when the engine is cold. Therefore, it seems unlikely that it would be the gauge (which has a line to the gauge, not electric). Also, a clogged screen would seem unlikely since the pressure is fine at idle and at running speed as long as the truck is not pulling a grade. But dropping the pan and cleaning the screen might not be a bad idea in any case. The oil, non-detergent 30W, is clear.

The only difference between hot and cold is the viscosity of the oil. So, a clog seems like a good guess since when the oil is hot it has no trouble getting through the blockage.

I once had a Chrysler Town and Country station wagon. The transmission ended up doing the same thing when the filters clogged. It would work fine once warmed up.

Tony this is a Herc not a GM motor.They have a small pump and not much screen area.
But I do understand....Anyone that's still using H.D. oil might have some kindda hard time understanding good advice....Bet you believe in Plastigauge and Bonne Ami
Seriously you might have a loose or cracked pickup
tube but I'd bet it's the screen

If my Diamond T was doing that I'd pull the pan

Could it be that there is a small portion on the pickup that is NOT clogged, and while going up a grade, the oil does not reach that spot ?