Maybe even stick a snake cam down one of the drain back holes and look for crud in the pan or drain all the oil an look in the pan they are so cheap.

Can't hurt to try.

 

Being slightly over doesn't cause an issue. I run about a quarter inch over the full mark as a habit. I'm pretty sure you're not a whole pint over as that would send it much higher on the stick. It would take much more than a pint to get to the point where the oil reaches the crank. If you reach that point, the oil gets whipped into a frothy foam which cannot lubricate your engine properly.

 

Sorry for the lapse in response... They have me working 10 hour shifts starting at 2AM, ugh. Did jump in and fire it up today, leaning away from the pump now (thank god). Let it idle a few then pumped the RPMs up and tried to bounce them a bit. Even 4500+ my oil pressure never dropped out. I didn't get a chance to cruise it to full temp, but if it was the pump or intermediate shaft I'm sure bouncing it some would have made it give up the goose. So good start! I'll try to get some time this Saturday to take it for a careful spin, get it up to temp, and see what it does. I'll have to pickup an oil change and figure out WHERE I can change it... :/ but beforehand I'll run a cleaner.

What suggestions you guys got? Seafoam, Marvels, Gumout?

 

Most of those want you to put about 500 miles on the engine before changing them out..... I would also be tempted to plumb in a mechanical gauge as well.... a 'backup' for the gauge in the dash, so to say.

 

Was able to do more of a test today, initially while cold everything was fine. Even at WOT and hitting redline to shift, everything was great. After getting up to temp and the oil warmed up (when you normally see the slight drop in pressure as the oil thins a little), then I was able to make the pressure drop out by getting into the pedal. First time I got it to happen, I pulled over and had to quickly turn it off and back on, then no problem getting it back home. While parked, I held 2000+ RPMs for a few seconds and it dropped out. When I let go of the gas and let it drop back down to idle, it took maybe 5 seconds before the oil gauge shoots back up to regular pressure.

 

Have you checked it with a mechanical gauge?

 

I have not, any real work/tests are almost impossible for me now. I moved into an apartment with strict "No vehicle work" clause in the lease. I used to be able to work on my vehicle at work (last thing I did was change the fuel pump in the back lot) but it went out of business because of Covid so I have nowhere I can actually pop the hood and work on it. I'm currently struggling to find somewhere to even change the oil without going to an oil change place (never used one, never will). Saw someone get their truck towed off while they were in the middle of changing the rear diff oil. They dropped the pan to let it drain and someone took them to get the oil while it was draining, it was gone when they came back. So I'm not gonna chance actually being under the hood for awhile doing tests.

Only place I really have is my brother's place, which is over 2 hours away and I'd have to plan a weekend or such to go out there to work on it, at my new job I haven't been there long enough to accrue any time off and I generally work at least one weekend day and can't get 2 days consecutively.... and it's getting colder... Ugh. So I'm gonna try the cheap maintenance ideas first before digging in, it already needs an oil change so tossing a cleaner or flush in isn't much. I know I *have* a sending unit socket, I just have to FIND it.

Can always hope the cheapest/simplest things are the fix right?

While we're on the subject though, I cannot find an accurate answer to the oil capacity of the 3.9L on a 98 (though the previous owner changed the engine, I think it's actually a 96 at least according to the paint pen writing on the block). I always thought something was wrong with the dipstick as what I generally find online and in the chilton manual says 4 quarts, but the dipstick reads right at the low line with 4.5 quarts and takes almost 6 quarts to reach the "full" mark of the safe zone. I generally try to aim for the middle of the safe zone (right at 5 quarts), but as I mentioned already I did accidentally go over it by about 1/4" on the stick after "topping" it off for a long trip.

EDIT: While trying to research possible causes, I keep coming across someone mentioning the exact same thing and it often says the oil filter. Found a post on a chevy forum from 2012 that says the exact problem I have. "I had a situation a few years back where my oil pressure on a 94 Dodge Dakota was running at about the mid point on the gauge at idle, but anything over 2000 RPM the oil pressure would drop to zero." they said it was apparently a bad batch of Fram filters.

Said post is here. I can't remember if last time I put a mopar or fram ultra on it, maybe the filter has gone bad? Too clogged?

 

The only way the filter should be able to affect oil pressure, is if it leaking. There is a bypass valve down there, so if the pressure differential across the filter is greater than about 7 pounds, oil will simply bypass the filter altogether. Changing the filter would be a quick and easy fix though...... and it likely wouldn't hurt in any event. Pay the oil change place if you have to. Cheaper than a new motor.

 

3.9L oil capacity copied from another site.

"From the FSM's:

'97-'98 is 3.5 qts w/filter.
'99 is 4.0 qts w/filter.
'00+ is 4.5 qts w/filter."

I've seen guys working on their cars in the parts store parking lots in certain parts of town. Choose your location wisely, pick a spot where you're out of the way and try to be quick.

The motor flush I occasionally use is Motor Medic five min flush.

 

out behind/aside a parts store is one option. O'R is usually pretty good about it. Ditto for side lot at a gas station.