Ok everyone, need some help again with our 2000 Durango 5.9l.

As some of you may remember, we had just rebuilt the 5.9l and got it running last Friday. We replaced the oil pump (being thorough) on the rebuild and used 10w30 Mobile 1 Full Synthetic (but not a Mobile 1 oil filter, dad cheeped out).

Upon start up, the oil pressure gauge goes to about 50 on the gauge, then settles down to about 40 under normal conditions. When the engine gets up to operating temp (210 deg) and we come to an idle/stop the oil pressure gauge drops to 0 and the check gauges light comes on and dings, give it a little throttle, and it comes back up to 40 psi as if nothing happened. Checked the oil level and it is perfectly filled and looking clean.We have put about 300 miles on it and it successfully passed Nevada smog Saturday with flying colors....no excess noise from the engine area, she's purring quite nicely. I also checked the plenum with my bore scope, no sign of oil so that is ruled out....any more suggestions?


Also as a minor side note, the passenger side freeze plugs appear to be "weeping" saw it for the first time this evening and it is a very minor amount,,,engine was too warm to get into tonight, but will be looking at it tomorrow...
Thanks in advance.

 

Replace the oil pressure sensor. That is a pretty common failure mode for them.

 

I've done the sensor exchange and substitution.

I've come to the conclusion...
The input device goes directly to the ECM, and the output device 'gauge' is driven over the network by the ECM.
In between is some code - probably set at book levels - say at less than 6 at idle for example ding the bell and show the gauge at zero.
(So a 5 at idle would be actually be fine, but the computer 'decides' it's bad.)
I also think the now 20 year old circuits have become a factor - some aging on the devices and reference voltages, and some corrosion on connections, and some rusty grounds - wouldn't be hard to lose a bit of voltage...

I do notice mine NEVER shows a decaying pressure like a real pressure gauge - it steps as though the ECM says 'show 80%, 40%, 20%, 0%'.

 

What brand sensor did you get? Wouldn't be the first time I got a bad part, right out of the box. Yours is showing typical behavior of a failed sensor......

 

Put a mechanical gauge on it. See what the pressure truly is.

 

Going to be doing that this afternoon when my dad gets here...he has the mechanical gauge...on a side note, I changed the oil filter to a Mobile 1 Synthetic grade filter...the generic one (cannot remember brand but think it was a Napa "house" brand), what came out of the filter was pitch black and the filter was quite heavy...starting it in the driveway, it acted more "normal"...i.e. upon startup about 60 on gauge, idle 40ish and with throttle pressure rises to about 50-60 ish...