I've started having issues with my oil pressure on the truck. When I start off, the gauge will read about 30, and will fade some after driving it for a while. However, it will sometimes drop completely when on an incline. This has mostly occurred in my driveway, when returning home after a drive.

If I shut the motor off, and give it some time to cool, the pressure reading will return to normal. I thought the problem was with the wire from the sender to the gauge (it was old and fraying). I replaced the wire, and all seemed well for a couple of days, and then the problem returned again today.

I checked the oil level, and while it was a little low, it was still within the "safe" mark on the dipstick.

 

I would put a mechanical guage on it to verify it's not the guage or sender. Good luck.

 

Are you running 12v? If so, how did you drop voltage to the gauges. 6v or 12v, I'd agree the gauge may be suspect, i.e. reading low all the time. If it's a real loss of pressure, it's time to tear the engine down.... could be a bad oil pump, more likely the bearings are at end of life.

 

Oil becomes less viscous as it warms up. A decrease in pressure is normal as the oil flows more easily through the lubrication system. How big of a drop are you seeing?

 

I'm running 12volt, with a runtz reducer on the gauge for the drop.

It starts off around 30, and may drop down to 15 while it's running. That doesn't worry me too much. It's the drop down to zero (or darn near zero) when on an incline that had me concerned.

 

Just a very WAG, but is your oil measuring dipstick positioned correctly? I mention this as I know of a very expensive International V8 where the guy had a similar problem..He though nothing of it until he blew the engine from low oil. The dipstick depth was wrong, the dipstick went in much farther than it should and gave an indication of having oil when there was not enough to reliably lubricate the engine.

 

Honestly, I can't say for certain that it is. I'll look into that.

 

What oil are you using? You should be putting in 5 qts, or 4.5 if the oil filter is still holding a half quart.

 

15w40. I'm pretty sure I put in 5 quarts with the last change.

 

Do you know how clean the engine is or is not, inside? Ross and I have both seen a flathead that was so coked with sludge under the intake manifold we wonder how the oil ever found its way back into the pan.

 

I never checked the top end. I did find sludge in the pan and in the filter can when I did my first oil change a few months back.

 

Yes....check the actual pressure with a test gauge!

If you are losing pressure, make sure that that the oil isn't thinned out by gasoline dilution. A bad fuel pump can sometimes cause raw gas to get into the oil & thin it out. If the oil is actually low & thinned with gas the level could look normal.

To verify, change the oil....mark the dipstick and test drive the truck. If the oil pressure holds with new oil....and the oil level doesn't increase, then maybe your old oil was ready for a change.

If the new oil doesn't solve the problem, the start looking for things like worn crankshaft bearings that let the warmed up oil leak out internally in the engine.

Dan

 

If your engine has not been reconditioned recently,
or original, I would not use a multi grade oil. I use
a 30W or 40W oil. Non or low detergent if it can be
found. If the engine is original and has been changed
to a high detergent multi grade oil than I suspect a
lot of gunk has came loose and is scoring brg's and
plugging passages. If so it's time for an over haul.
But I have got a few more years out of a Y Block by
just flushing her with Diesel than running 40W oil.
She is good till she starts knocking. JMHO and .02

 

The pressure dropping off on a hill is perplexing. Is this only on a hill where the engine RPM drops significantly or on any incline? Like if you were parked on your driveway at a slant, does pressure drop? The oil pump and pickup are at the rear of the engine, so if anything I'd expect it to drop going downhill, but that makes no sense either unless your oil level was WAY low.

 

It would be interesting to clarify if the incline is nose down or nose up incline. Side note: Y blocks in trucks are notorious for loosing oil pressure in a nose down or hard braking due to the nearly flat oil pan.