Oil Pressure mystery........

[KevinP73]

I've got a 2000 Dakota with a 4.7 automatic 2wheel drive. The engines has 198000 on it. Rebuilt at 146000 and it's been trouble free since then. Recently I noticed the oil pressure gauge doesn't show any more than 40lbs at speed. Now here's the mystery. Lately the gauge will drop, at idle or after a sudden deceleration, to 0lbs and the "check gauges" light will come on. It will most often regain pressure once I accelerate again. Sometimes it doesn't. Checking the oil shows I'm full on the stick. Even when running with no pressure indicated there is no change in the sound of the engine. I'd expect some noise if I were running 60mph for ten minutes with no oil pressure at all. I've replaced the pressure switch but that didn't change anything.
What do you think the issue is?

[LEAKYSEALS951]

I have a friend with a boat with the same problem.
He always assumed it was the oil pump.
Turned out it was the sender.

Your sender is new.

I will throw out a longshot idea short of getting a new pump.

The oil bypass valve has crud in it. Also check the ground on the sender.

Happened to my 951/bypass.- but it cut off all pressure- and the lifters did collapse after a while.


Long shot thoughts.
Good luck.

[Dan J]

Check with mechanical gauge?

[masraum]

Originally Posted by Dan J

Check with mechanical gauge?

^ This, cheap mechanical gauge from a parts place.

[fanaudical]

I've read that the Dodge 4.7 V8 has an esoteric problem: When the engine oil fill housing gets gunked up with oil emulsion stuff it somehow blocks the PCV valve which in turn somehow causes low oil pressure readings. It can't hurt to clean it. (I ran across this while researching used trucks last summer.)

You might also check the wiring from the pressure sender to the gauge; make sure nothing has affected the resistance (like a bad connector or something).

[Gogar]

Is it possible that there is a "Pressure Switch", i.e. Idiot light, and then -also- a pressure sender? maybe you replaced the pressure switch but the pressure sender is actually the culprit.

Sort of like a 911.

[KevinP73]

Originally Posted by Dan J

Check with mechanical gauge?

Would be a logical step in resolving the problem but......... I'm convinced it is developing sufficient oil pressure. Just don't know why the stock hardware/sensors/gauges isn't reading it. And that's the issue I'd like to solve.

[KevinP73]

Originally Posted by Gogar

Is it possible that there is a "Pressure Switch", i.e. Idiot light, and then -also- a pressure sender? maybe you replaced the pressure switch but the pressure sender is actually the culprit.

Sort of like a 911.

Checked this before I replaced the switch. There is only one switch related to the oil pressure.

[KevinP73]

Originally Posted by fanaudical

I've read that the Dodge 4.7 V8 has an esoteric problem: When the engine oil fill housing gets gunked up with oil emulsion stuff it somehow blocks the PCV valve which in turn somehow causes low oil pressure readings. It can't hurt to clean it. (I ran across this while researching used trucks last summer.)

You might also check the wiring from the pressure sender to the gauge; make sure nothing has affected the resistance (like a bad connector or something).

I've heard the same thing. The housing was all gunked up at the last oil change and was removed and cleaned. The rest of the PVC system might be due to some routine cleaning.

[fred cook]

Try pulling the connector off the oil pressure sender and spraying the inside of the connector with some electrical cleaner spray. The company that I worked for had some Chrysler product pool cars and they experienced the same type of problem from time to time. Good luck!

[yetibone]

Is the oil pressure switch a Mopar part, or aftermarket? I've always had to get oil pressure switches for Chrysler vehicles from the dealer, because they're the only people that carry the correct type.

Every aftermarket oil pressure switch I found for a Chrysler was actually a variable resistance sender with two terminals, but the OEM sender is a single wire switch that grounds it's terminal to it's brass casing. The aftermarket sender will provide enough continuity to make the light flicker when there's drastic drop in pressure, like coming down to idle. The OEM switch doesn't have any continuity at all until ~3 psi.

If in the past some oil leaked out of a bad oil pressure switch and walked up into the casing of the wire, that can also contribute to the continuity necessary to light up the warning on the gauge cluster.

[cstreit]

I'd definitely validate if you're actually losing pressure or it's a sensor malfunction. You have to know this first. Mechanical gauge.

[asphaltgambler]

^^^^^^^ THIS^^^^^^^^^^^^^^^^

You can only rule out the impossible by actually confirming what is going on, piece by piece, then only the possible cause remains.........................................