hey i have a 98 dakota with the 3.9. it is on it's second engine because of the same oil pressure problem.......pressure just drops off after a while......no pressure at all! then it will come back if it sits for bit....then maybe go away foe a few months after fresh oil, then drop off again. really strange because it's happened on two different engines around the same miles....?!?!?!?!!?
WHY!!!!???!!!!!!????

 

well I'm not sure if a new engine included all the other parts (aka a new oil pump and new oil pick up) if it didn't then i would think that they'd be the culprit. If both those things were replaced as well then I have no clue.

 

yup...all of those things were replaced.

 

How much oil is in it before you change it and it comes back

 

oil levels are all normal.
i have been told sludgy oil build up clogging the pump screen, faulty check valve in the pump itself, holes in the valley wont let it drain back down to the pan fast enough, ect...ect.... BUT why would it do the same thing on two different engines???

 

Another thing that could cause it would be overfilling with oil causing slosh by the crankshaft which in turn causes the oil to foam and show no oil press since it's full of air.

 

hmmmmmm well since everything mechanical was fixed then I would lean more torwards the gage or sensor being bad.

 

Zanethan has a point, could be a faulty pressure switch and or sending unit

 

i had thought about that too.......but when the oil pressure drops you can also hear the result of the oil loss in the engine. it starts ticking and sounding pretty bad if you dont stop right away.

 

I know this is probably a dumb question but are you using the right weight oil?