have a 1999 dodge ram van 1500 with almost 90000 miles after being driven awhile and warmed up when coming to a stop the oil pressure gauge drops to 0 really fast. There is no abnormal engine noise of any kind. Could this be the oil sending unit and if so where is it at?

 

Try changing oil and filter first. You might have a cheap oil filter problem.

 

Change the oil. When I got my van, changing out whatever was in there with a Mopar filter and Mobil Super 5000 oil netted me 30-40 lbs. of oil pressure back.

 

The reason I installed a mechanical oil pressure gauge is because the dashboard ones are slow and inaccurate at best.

I was gonna buy a real tester but a dashboard gauge was less money. I 'T'd' the line so that my stock gauge still works. The Dash gauge is about 45 seconds behind the mechanical which responds nearly instantly to increasing RPM

When cold, the max PSI is 68 PSI at 800 rpm, or at 4000rpm. 68psi is the oil pump relief pressure.

When hot this drops to ~63 psi

But at 550 rpm hot as it gets idle, I get 18 PSI with M1 TDT 5w-40 in the sump.

63 PSI is reached, when hot, at 1900 to 2100 rpm.



My factory service manual says 8 to 40 psi at idle is acceptable.

Some oils shear out of grade with age and abuse.

Sometimes fuel dilution in the oil will thin the oil and reduce it's viscosity so less psi makes it to the sender.

 

I would say it's either low on oil or there may be a problem with the oil pickup. When mine got a little over a quart low last year my oil pressure gauge would drop to 0 on hard stops and the check engine light would flash on for a second. After a second the oil level would recover and the pressure returned. Safe to say I keep a closer eye on the oil level now

 

are you sure you aren't dumping coolant from the intake or head gasket into the pan? That would cause your problem. Just a thought..BTW coolant settles below oil...

 

A mechanical gauge will help you figure the problem, at
the moment the true oil pressure is unknown.

The factory gauge is just not trust worthy.