samsmith084

Recently bough a 2001 XJ with the 4.0. Had this engine before in a wrangler and loved it. the engine is running well without any noises, but the oil pressure seems to be acting up.

Before describing the situation, I should explain I have replaced the Oil Pressure Sensor, as well as cleaned the fitting and the entrance to the sensor.

When idling, the gauge reads zero. When driving, it begins to rise at 1700 and above or so. It gets to about 20-25 max, and always returns to zero once stopped.

I've been driving all day, and no noises have come about, however anytime the oil pressure reads low readings, concerns follow. What could be wrong?

Thanks in advance.

BlueRidgeMark

First step is to...... wait, no. The first step is to say welcome to the forum!

The second step is to verify the oil pressure with a good mechanical gauge. You can buy a , or you can pop over to your local auto parts store and pick up .

When I needed to do this, I got a Bosch from PepBoys. Less than twenty bucks out the door. Once I got home, I disconnected the factory sending unit, set the Bosch up on my cowling where I could see it, connected it to the sending unit port, fired up the Jeep and had an accurate reading. Revved it a few times to see what it did up to redline. Then I shut it down, and put everything back to stock. All of that took about 10 minutes.

That was 2 Cherokees ago and I still have the gauge.

Aftermarket sensors are notoriously inaccurate. Any problems with oil pressure MUST be verified. If the oil pressure is fine (it probably will be) but the guage is flaky, it's either a bad sending unit, or there's a problem with the wiring to the sending unit.

Bugout4x4

This brings up something I always wanted to ask about. Someone mentioned that bad O-rings in the adapter could do this also. But... it has always been my experience that once a system is up to pressure it should be the same pressure throughout the whole system as long as there are no big leaks of course. What are your thoughts on this? Is this possible?

samsmith084

Thank you for the Welcome and the quick reply!

I'm assuming you mean yo attach the gauge to the actual sending unit toward the rear of the motor, not the oil pressure senor I replaced, which is on the side above the oil filter?

Also if this helps narrow it down, I put in some of the Lucas chemical to thicken the oil, but the gauge activity didn't change

KenR

Unscrew the existing oil pressure sending unit, screw in the new sending unit that came with the mechanical gauge. Make sure the tubing is attached to the new gauge. Start engine, look at pressure on gauge and look for any leaks. 20psi or better? Great! 0psi? No freaking good.
Please report back.

BlueRidgeMark

Thanks, Ken.




I don't see how bad o-ring could do that, but I'm open to hearing other viewpoints on it.

Not on this guy's thread, though!

Bugout4x4

If the O-ring issue could also cause his "what could be wrong" issue then it does apply correctly to this thread Mark. I was hoping you might have the answer off the top of your head to either eliminate the possibility or confirm the possibility of this also being a cause for his particular situation. Trying to cover ALL possibilities to help him man.

samsmith084

Unfortunately, After installing the gauge, I found it red 3psi at idle, and 25-30 at 4000RPM....

Into the garage she goes! So, next question. where to go from here? Some information about the jeepy, its got 185000 miles on it. So the fix, if in-depth, which I know it will be, what can we do to be as complete as possible while inside.

00t444e

Does it make any noise, and what kind of oil and filter are you using? You could try switching to a 15w40 Diesel motor oil and a good oil filter like a Purilator, Mopar, Wix, or Motorcraft, and see if that helps.

Bugout4x4

I waited for Mark to reply before I jumped back in. Because this just became a whole lot more complicated. Now the engine may have to come out and apart. Even if it is just the oil pump there is also probably already damage from the low oil pressure issue.

This is why I was curious about the filter adapter O-rings, it would be one of the last "easy" fixes left. My engine is newly rebuilt and doing almost the same thing yours is but not quite as bad. So the adapter curiosity is for myself also. I was hoping to hear that the O-ring issue WILL cause pressure (reading) problems.

There are a lot of other things that could cause this. But they are all internal. How deep are you ready to go? It could mean a full rebuild. Have you ever done this before? Are you up for it?

There is a lot of help here for that if you are willing to do the time and work, but at this point it is worst case scenario. First thing pan off and inspection. This can be done while in the vehicle, but it's a bit of work to get it off if it is stock.