oil pressure dropping as RPM increase

[chrisj750]

'95 F350, been sitting for about 2 years now. Finished fixing my UVC Harness and glow plugs last night. Runs really smooth. BUT NOW the oil pressure guage in the dash starts to drop as the RPMs reach 2000 and by 3000 it hits the low end of the dial. Same in neutral or driving, power does not seem to diminish. Oil level is middle of marks on dipstick. Any ideas?

[JSchuricht]

Is the oil and filter 2 years old? IIRC that sensor is located in the reservoir for the HPOP, you might try cleaning/replacing it.

[chrisj750]

New oil and filter. Will clean the sensor tomorrow.

[Patrick Feeley]

Unless you have an aftermarket gauge and sender, note that the factory setup just has an "idiot" gauge triggered by a switch (on the HPOP reservoir). The gauge is supposed to read mid-scale at any pressure over the switch setpoint (something like 6 psi). Cheers!

[chrisj750]

That's the funny part, it tracks the higher RPMs repeatably and always at the same location on the dial.

[chrisj750]

Thank you JSchuricht,
A wise man once told me "the more positive you are you are right, the more probable you are wrong. "
Rechecked the oil we put in the truck,,,(awkward silence) it appears when I said synthetic oil I neglected to say DIESEL OIL. Synthetic 5w- something CAR oil!!! 3 gallons of the right stuff and another filter later and this truck problem is fixed.

[chrisj750]

One of these days I am going to check the output of the oil pressure switch and see if it is a pressure sender and modded dash dial to turn it into a proper analog dial.

[madpogue]

Originally Posted by chrisj750

One of these days I am going to check the output of the oil pressure switch and see if it is a pressure sender and modded dash dial to turn it into a proper analog dial.

Do some poking around online; I think this has been done. IIRC, it requires desoldering a resistor on the back of the dial, and a real sender rather than just an on-off pressure switch on the motor. It's on one of the forums; I just don't know what you'd use as search terms.

[chrisj750]

Actually there is a 20 ohm resister you need to short (solder a wire across it) and use a pressure sender unit from a vehicle with a real gauge.
Biggest hassle is getting the dash out.

[Patrick Feeley]

Here's the article: "Real Oil Pressure Gauge". I did this mod on my old 94 many years ago and it was OK, but not great (not a lot of range on the gauge). I eventually went back to stock on that gauge and put in an aftermarket OP gauge. Cheers!