I've been periodically working on this 99 durango 5.2l for 5 years. I will think I figured out the issue and I drive around the block and ding goes the cluster. So I'll list the new parts and a short run down on what's been done. First was a cleaning of sludge oil pan off and pan gasket replaced then timing chain with waterpump, thermostat ect. Got a mechanical gadget instead of the oil sensor to get real reading and same outcome. Then new oil pump have used different oils and additives so if anyone has any advise it would be a durango saver.. thinking of putting an ls1 in it somehow. Couldn't be as much work as this 318 has needed ..

 

If a mechanical gauge is telling you that you have zero oil pressure when warmed up, it's time for a new motor.....

 

Did you put a stock or high volume pump in the engine? How many miles on the engine? If you got the pickup screen clean, a high volume oil pump might get some extra life out of the engine but it's probably nearing the end of its service life. Note, high VOLUME is good. High pressure will blow the seals out inside and they are probably worn already.

 

So no on the high volume I went oem . 180,000 on the engthe.ive had the pan off 2wice now and cleaned and lubed everything up the bearings had no movement besides a Lil side to side play the cylinder walls looked great I was actually very surprised I did cut the wind age plate in the pan out cause the limited space to get the pan out I wanted the pickup tube exactly were I put it . What can cause the engine to loose pressure after the thermostat opens . Plenum gasket just arrived so off comes the top of the engine

 

By "gadget" you mean gauge? What psi are you seeing at start up/operating temp? What oil are you using?

 

Well the plenum had one bolt broken on the frontleft or right sitting in the truck. But it had been able to seep air. And now the aluminum is rotted by the hole I'll include pictures the engine has so much carbon build up in it and doing a diesel flush just broke it all loose.

 

40 psi at start up and with throttles jumping to 60 and after the thermostat would open and water circulated pressure would drop to 5psi to low for the electric sender to read. It never chattered with valve noise could the oil have gotten stuck in the top of the engine from all the build up

 

Clean it out thoroughly, put it back together, see if the problem is gone....

If it was just a matter of oil being trapped in the top of the motor, that would happen LONG before the engine got up to temp...... Putting a mechanical gauge on it, and running a test would tell you if its a simple problem or not. (bad sender..... it happens.)

 

I checked the dipstick prior to starting it and then I cranked the engine over and it wasn't starting but I grabbed the lipstick again and the oil level had dropped to about half way point between add line and tip of stick. So it's not returning as it should I think so engine running warms the oil and it flows better... idk it's got me totally frustrated. I have valve covers off is there anything I should do in there. Besides seals .

 

Looks like there is a oil tube hooked up to it so I would assume it has one.
With that amount of stuff up top I would drop the pan and see what the pick up screen looks like. Bet you will find crud in it.