I have a 99 1500 with 90k on it. Fresh oil change 1500mi ago.
Gauge reads fine then will slam to zero then will jump back to normal.
problem only occurs at lower than 2000rpm (65 mph- gauge works fine).
no other idiot lites... except for Check Gauges.

Even when gauge sits at zero for 30-40 sec... no increase in engine temp,
no peculiar sounds from engine...I'm thinking it has to be the sending unit or a flap of sludge on the unit's sensor
that increased flow due to rpm will keep it lifted off sensor.
if it was the pump and I truly was getting no oil flow- then engine temp would be rising, correct?

I've also heard I need to buy a special socket to get that thing out... is that true?

Thanks for any input!

 

Its the sending unit. Happened to the old mans truck. Same story. Its hard as hell to get to cause its basically on the firewall along w/ the motor. Use a mirror to help locate it. i dont think there was a special socket (not sure tho cause we have so many tools it might have been "special") Best way to find out if you need a special socket, go to the parts store, get the sending unit, and ask the guy at the counter. If he doesn't know, walk over to the tools area and try sticking a socket on there. good luck, and be carefull not to break it off in there, its like a spark plug!

 

its on the extreme back edge of the block, about the center of the motor. just beside the distributor. i changed mine when i had the intake off simply because i could see it. if you remove the air filter box you should be able to feel it. a short wrench should be all you need, other than longer arms and extra eyes...

here's a pic, except it sits vertical on the back of the block.
http://info.rockauto.com/SMP/SMPDetail2.html?PS291.jpg

 

Auto-zone carries the socket to fit the sending unit.

 

put the new one in... turned engine on- went up to 65 on the gauge... sat there for 10 sec. then dropped back to normal- just under 40. Then... BAM.... slammed back to ZERO.


Any suggestions on what to do next? had a 3mo/3,000 warranty that expired 500 mi before all this : (

 

a few thoughts, some may be stupid.
i think oil pressure is determined by the pump's volume pushing against the tiny oil passages in the bearings.
flashbacks from high school were something about pressure and volume...
this is a fixed thing based on big hunks of metal and tolerances, etc, etc.
you have good oil pressure at times, so that indicates your bearings are normal.
i've read other posts on here with similar problems, but i don't think anyone ever posted their solution, other than a sending unit or an oil pump.
i can't see any reason why the oil pump would kick in and out. its all iron. it should either work all the time, or not work at all.
i'm wondering if a piece of sludge is sitting in your sending unit passage, occasionally blocking pressure to the unit. just a thought. if so, could it be dislodged by removing the sending unit and running the motor to let it pump it out. again, just a stupid thought.
you might want to rig up a real live external gauge and see if it reads the same. your dash gauge is controlled by the pcm, with the sending unit as an input. its not a direct feed.
you might try a motor oil flush, where you add it and let it run for a few minutes and then change the oil. -even with this i would be tempted to remove the sending unit and let it pump out a little.

 

I think the ol' bulldog is onto something here. Sounds like an intermittant blockage either at the sending unit or the pick up tube/screen. Try removing the sending unit and rig up a plumbing fitting and hose to a jug or something with a screen/sock in it and try flushing as he says. If no boogers fly out then it may well be in the lower end bouncing around the pick-up.(less likely)

 

Sounds like a tough problem.

It was correct to suspect the oil pressure sender because many have gone bad.
It still could be a broken wire that is occasionally losing contact.
You could rule out the broken wire possibility
by hooking up the mechanical pressure gauge.

Dropping the oil pan will let you look at the oil pickup inlet
which can become clogged with debris.

A mostly clogged inlet
and a big piece of debris that sometimes floats over and totally
blocks the inlet could cause these symptoms.

I guess it is also possible that the oil pump drive shaft
could have wallowed out the socket enough that sometimes
it gets driven when cold then begins slipping when it gets hot.

 

Thanks for all the info- am flushing and getting a OC today and will flush out the sending unit channel.... will update afterwards...

You guys are great- all the help was much appreciated...

 

was also a touch more than a quart low... never suspected that 1500 mi into an oil change and NO LEAKS... but a leaking plenum gasket AND hauling a few heavy loads might be able to explain the oil loss... but flush and change and the gauge is performing tiptop. Thanks Again.