steve.caruso1

The symptoms:
* In and around town oil pressure stays constant around 30-40 while driving, drops to about 13-15 while stopped at lights.
* Long highway driving (20 minutes +) OP drops to zero and check gauges light comes on. Tap the gas, goes back up to 10-12, light goes off.
The history:
* Few months ago I replaced a cracked head and intake.
* Replaced the oil pressure sensor with a molar replacement
* Oil change with the correct oil/filer

Is the next logical step to replace the oil pump and pick-up?

SteveMongr

I'm no expert but am in a similar situation. Knowing that the head was cracked, the loss of oil pressure at hot idle is a sign of worn bearings in the engine. It is best to verify the readings with a mechanical gauge. Oil pump will not help if it is the bearings that are worn. Will eventually require an engine rebuild or replacement.

XJRed96

I'm more inclined to suspect a faulty sensor, even though you said its a mopar sensor. Try giving the sensor itself a few light taps next time the gauge bottoms out and see if it makes a difference. If its still under warranty I would try and get a replacement. If it was a mechanical issue id be more inclined to say you would have low oil pressure all the time not just sometimes, and when the pressure did drop, it would not want to jump back up and stay up. while you have the sensor out, as already suggested, I would hook up a mechanical gauge and get some legitimate readings. also back track the harness as far as you can to make sure there are no damaged wires or anything.

moparado

Was the oil pressure also 13-15 hot idle and drop to 0 for long trips 'before' the head replacement? Any engine knocks or ticks?

As others said, measure the pressure with a real gauge to verify the cluster gauge.
If it turns out the sender is accurate, your engine is not long for this world.

steve.caruso1

Are you talking about the main bearing?

tjwalker

Mechanical gauge oil pressure test must be performed next.

Gotta know true oil pressure readings.

steve.caruso1

The oil pressure did not drop to zero prior to the cracked head. I don't know if the two events are associated but I suspect they are. When the oil pressure drops to zero there are no associated symptoms. No knocking, pinging, just the gauge reading zero.

Thanks for the feedback, I'll get an independent gauge today and test it out, hopefully it's a faulty gauge.

I checked the wiring harness from the oil pressure sensor back to the firewall, no cuts or damage.

I was planning on dropping the pan this weekend to see if the pick-up may be clogged but you make a good point. If it were clogged it would show sporadic feedback at normal operating temperature, not only when it's hot after a long long drive. So let's say I drop the pan and as expected everything looks fine, what next?

BlueRidgeMark

No, no, no. Quite jumping to conclusions! He clearly said he replaced a tooth!

See?


This car needs a dentist, not a mechanic!




Okay, kidding aside, Steve, you can get a decent Bosch gauge for under 20 bucks. I did this last year and it took me all of about 5 minutes to disconnect the sending unit, connect the Bosch in its place, and get a reading. I just laid the tube across the engine compartment and put the gauge on the cowl where I could see it from the driver's seat. Fired it up and found I had decent pressure.

In your case, I think the evidence points to a bad news story. Cam bearing or main bearings, or both.

steve.caruso1

I appreciate the dentist joke! That's what you get for typing on the phone. Yes, the sensor is a MOPAR not Molar. I'm going to stop at Napa on my way into work and pick up that other gauge. That's a good idea about just keeping Outside. I'll let you know tonight if the pressure reads the same. Thanks again.

killbox916

It takes about 20+ minutes for the oil to get up to full temp and the oil to thin out. How long did it run with a cracked head?

If I had to guess, you may have mixed some coolant in with the oil and cooked the main bearings. Or cooked them from the heat.

As the other person said you are due an engine rebuild if your oil pressure is really that low.

steve.caruso1

The head was cracked for about 2 weeks before I noticed what was going on. There was water in the oil when I checked it then replaced the head and intake.

BlueRidgeMark

Yeah, that's not sounding very good. This engine's gotten a little long in the tooth. You might just have to bite the bullet and rebuild it.

But don't go getting down in the mouth - it's a good project you can sink your teeth into.

Brace yourself for some weekends turning wrenches. And to crown it all, you'll have a fresh engine ready to go another 400,000 miles!


/ducks/

XJRed96

i'm still of the inclination that its electrical, likely the sensor. because i'm still of the mindset that if it was mechanical it wouldn't come and go like it is. however there are extenuating circumstances that may allow for that.. most mopar oil pressure sensors (and their aftermarket counterparts) are generally of weak quality. 10-12 psi at a hot idle(which is spec) is low enough for a faulty sensor to register a zero. this goes for town and countrys, pt cruisers, neons, jeeps, etc. but speculation shall soon come to and end once we get some actual readings.

I knew i had a cracked head shortly after i bought my jeep and drove it for a while like that. no coolant or oil contamination just a starting issue after long drives when coolant would be allowed to enter the combustion chamber. it never overheated and kept the coolant level topped off to avoid this. But i also have a similiar issue you are experiencing where after the sensor got nice and hot and sat for a little bit it would often read zero. a few quick blips of the throttle the pressure would spike and the pressure reads fine. if i got out and tap the sensor with a wrench or something it would read normal.... sometimes the hammer(or hammer like object) can be a great diagnosis tool. starters. fuel pumps. window motors.

steve.caruso1

Update:

Ok so I went ahead and had the oil pump, puck-up and rear main seal replaced to hopefully fix this issue; I had a local 4X4 shop do the work because I simply don't have the time. I trust these guys and they do great work at a fair price. While the mechanic had the pan off he took a look at the bearings and crank, said everything looks great. Again, this 4.0 only has 90,000 miles on it so that's kind of what I expected. I'll take it on a long drive over the weekend but he's confident the new high volume pump will fix this issue.

So onto another issue! When the engine is hot and I stop then restart the motor it *****es and wines like a SOB. Then I get the check engine light with error code 301,302,303. Any thoughts on what may be causing this? Fuel Pressure? Injectors?

BlueRidgeMark

If a high volume pump "fixes" the issue, well....