89 Dakota Oil Pressure Drop - New Engine

Hello, I’ve got an 89 Dodge Dakota with the 3.9L V6. I rebuilt an engine (new bearings and all) back in December and dropped it in. It has run flawlessly for about 3000 miles. I left for vacation for a week, returned, and noticed the oil pressure dropping while I’m not on the gas pedal. The sending unit had oil all over it, so I replaced it. I’m still having low oil pressure reported at times, even though it’s running strong and I don’t hear anything amiss. I know the usual causes are worn bearings and pathways for oil, but the engine only had 80k miles on it… looked to be in great shape, and that was before I rebuilt it. I really doubt there is excessive wear after only 3000 miles of break in driving. What should I do?

The first thing to do is to install a calibrated, mechanical gauge and observe the actual pressure. You probably need to keep it attached until you get the engine and oil fully warmed up.

After you have the actual numbers, you will have to decide if the idle oil pressure is out of tolerence or too near to the bottom limit.

Get back to us with the numbers and your assessment of the situation.

Thanks for the reply. I’ll see if I can rent one from O’Reilly tonight.

Well, they don’t rent them but they have one for purchase for $15.99. I’ll just buy one and see how it goes.

Ok, all they had was an 8.99 one, so I installed it. The needle isn’t even budging at all… although since it’s just dangling in the engine compartment I can’t watch it and drive at the same time. Is an 8.99 oil pressure gauge a waste of time, or do I really have 0 oil pressure?

Your Dodge needed a “rebuild” at 80K this is the first red flag. Now 3000 later oil pressure problems,did your rebuild fail to address the cause of the 80K engine failure?

Oh, I should have explained. I bought the truck with a bum engine from a farmer for 500 bucks. I bought an 80k mile engine out of a wrecked truck at a junkyard and disassembled it and rebuilt, since it was super easy with it in the garage and on a stand. While I was rebuilding I noticed the condition of the junkyard engine was very clean and well maintained… it probably didn’t even need a rebuild.

I just picked up a high volume oil pump and will try to get it installed in the next few days.

Again what told you to rebuild a 80K junkyard engine? just because it was easy to get to? I would maybe have pulled the pan and a rod cap,more likely just put it in and ran it. What I am getting at is the problem is probably something you did or didn’t do at rebuild time.

If a new oil pump does not correct the problem you will have to check the clearances on the main and rod bearings. How did the crank look any scoring ? If there was any scoring on the crank it will trash the bearings. Was the screen on the oil pump clean ? Strange thing is you said everything was good until the vehicle sat for a week.

One of the hardest things about doing this type of diagnosis is deciding what info that the OP provides is just clutter and should be rejected.

Some of my favorites are “ever since I hit a pot hole” or “ever since I had to brake hard” and then there is the great " I put in 10w 30 when I called for 5w 20 and now my car won’t start",just have to filter it out (not the oil, the info.)

Well, I hope the high volume pump takes care of it. There wasn’t any scoring or other damage inside… it looked like a very well maintained engine. I rebuilt it because it was easy to do and parts were relatively cheap. I figured starting over at 0 was better than starting at 80k.