2003 TJ oil pressure issue

[BOBDOUGIE]

I am brand new on the web sight. So pardon me if I l sound like the amateur that I am. I have an extensive career in the EQ Repair. I have worked on my vehicles as much as possible (90% of the time).

I have a 2003 TJ that lost oil pressure and the check engine light came on. Stopped and checked the oil level was good. Towed it home as no oil pressure is serious. installed manual gauge with the sender. When testing it worked fine until I got back to the house and then the oil pressure gauge on the dash dropped, not to the point that the ck gauge came on. But the manual Gauge showed 45 psi up until then. Then it dropped to 5 to 10 psi at the same time as the dash gauge went down. I am thinking oil pump or suction leak on pick up tube. But I don't want to pull all of that apart before I have checked everything possible externally. Is there anything else I can test before I pull the oil pan? All of this is based on my EQ experience.

Thanks for any guidance you can give

 

[Chris]

I am brand new on the web sight. So pardon me if I l sound like the amateur that I am. I have an extensive career in the EQ Repair. I have worked on my vehicles as much as possible (90% of the time).

I have a 2003 TJ that lost oil pressure and the check engine light came on. Stopped and checked the oil level was good. Towed it home as no oil pressure is serious. installed manual gauge with the sender. When testing it worked fine until I got back to the house and then the oil pressure gauge on the dash dropped, not to the point that the ck gauge came on. But the manual Gauge showed 45 psi up until then. Then it dropped to 5 to 10 psi at the same time as the dash gauge went down. I am thinking oil pump or suction leak on pick up tube. But I don't want to pull all of that apart before I have checked everything possible externally. Is there anything else I can test before I pull the oil pan? All of this is based on my EQ experience.

Thanks for any guidance you can give

Here are a few other things you might want to check before taking apart the oil system:

Start by inspecting or even replacing the oil filter. A clogged or faulty filter can restrict oil flow, leading to pressure drops.

Check the condition of the oil. If it’s old or contaminated, it may not be providing adequate lubrication, which could affect pressure.

You mentioned the oil level was good, but double-check it again to be absolutely sure, especially after the vehicle has sat for a while.

The sending unit itself can sometimes fail or give inaccurate readings. If you have a spare, try swapping it out to see if it resolves the issue.

Inspect the wiring and connections to the gauges and sending unit. Any corrosion or loose connections could lead to incorrect readings.

Look for any signs of engine wear that could affect oil pressure, such as worn bearings or excessive clearances.

If everything checks out and you still haven’t resolved the issue, then moving on to inspect the oil pump and pickup tube would be your next step. Good luck, and keep us updated on your findings!

 

[BOBDOUGIE]

Here are a few other things you might want to check before taking apart the oil system:

Start by inspecting or even replacing the oil filter. A clogged or faulty filter can restrict oil flow, leading to pressure drops.

Check the condition of the oil. If it’s old or contaminated, it may not be providing adequate lubrication, which could affect pressure.

You mentioned the oil level was good, but double-check it again to be absolutely sure, especially after the vehicle has sat for a while.

The sending unit itself can sometimes fail or give inaccurate readings. If you have a spare, try swapping it out to see if it resolves the issue.

Inspect the wiring and connections to the gauges and sending unit. Any corrosion or loose connections could lead to incorrect readings.

Look for any signs of engine wear that could affect oil pressure, such as worn bearings or excessive clearances.

If everything checks out and you still haven’t resolved the issue, then moving on to inspect the oil pump and pickup tube would be your next step. Good luck, and keep us updated on your findings!

Thank you for your response. The reason I don't think it is a sender or wiring is that the manual gauge drops at the same time as the oem gauge. The pressure does not drop until the eng warms completely up and then you go to idle. You can watch the pressure fluctuate as you rev the eng a bit. The oil was changed less than 1000 miles ago. But that does not mean the new filter is not bad. Have had new parts be bad from the factory. Kind of like the after market senders. There is no blow bye, no exhaust smoke or oil leaks. This jeep was driven by a high school Girl, It was in super condition when I got it. We figured if we had to pull the pan, we would look at a rod and main brg while there.

Thanks Bobdougie

 

[BOBDOUGIE]

Also Chris being new to the forum, am I in the category for this topic?

 

[ColoJeep]

Thank you for your response. The reason I don't think it is a sender or wiring is that the manual gauge drops at the same time as the oem gauge. The pressure does not drop until the eng warms completely up and then you go to idle. You can watch the pressure fluctuate as you rev the eng a bit. The oil was changed less than 1000 miles ago. But that does not mean the new filter is not bad. Have had new parts be bad from the factory. Kind of like the after market senders. There is no blow bye, no exhaust smoke or oil leaks. This jeep was driven by a high school Girl, It was in super condition when I got it. We figured if we had to pull the pan, we would look at a rod and main brg while there.

Thanks Bobdougie

How many miles on the engine?

 

[Bammo68]

I have a 2003 TJ that lost oil pressure and the check engine light came on. Stopped and checked the oil level was good. Towed it home as no oil pressure is serious. installed manual gauge with the sender. When testing it worked fine until I got back to the house and then the oil pressure gauge on the dash dropped, not to the point that the ck gauge came on.
Thanks for any guidance you can give

I can only share my experience with this issue but if you google you will find a lot of similar stories. I have a '99 with 90K Miles. Oil pressure sits about 21 psi when warming up or under gentle load. When hot and you come to a stop the indicated pressure drops to zero and check gauge light came on. I swapped pressure sender transducer and no change. A manual gauge showed similar results.

I know the later model TJ's have a "Dumb" sensor but that's not what is happening here. I built a new engine and installed it over Xmas. Oil pressure hasn't dropped below 40psi since and usually sits about 50psi. Tried both original sender and replacement and same same so it wasn't an instrumentation issue.

I'm going to pull the bottom end off the original motor to see if there is any clue as to the reason in the bearings - noting the engine itself ran perfectly and pulled like a bus load of Catholic schoolboys so whatever the issue is it didn't seem to be manifesting (yet) in the motor itself.

<EDIT> I built the new motor on a different block for fun, not because of the oil pressure issue. Will advise once I get the bottom end apart.

 

[BOBDOUGIE]

How many miles on the engine?

This Jeep has 185K miles.

 

[BOBDOUGIE]

I can only share my experience with this issue but if you google you will find a lot of similar stories. I have a '99 with 90K Miles. Oil pressure sits about 21 psi when warming up or under gentle load. When hot and you come to a stop the indicated pressure drops to zero and check gauge light came on. I swapped pressure sender transducer and no change. A manual gauge showed similar results.

I know the later model TJ's have a "Dumb" sensor but that's not what is happening here. I built a new engine and installed it over Xmas. Oil pressure hasn't dropped below 40psi since and usually sits about 50psi. Tried both original sender and replacement and same same so it wasn't an instrumentation issue.

I'm going to pull the bottom end off the original motor to see if there is any clue as to the reason in the bearings - noting the engine itself ran perfectly and pulled like a bus load of Catholic schoolboys so whatever the issue is it didn't seem to be manifesting (yet) in the motor itself.

<EDIT> I built the new motor on a different block for fun, not because of the oil pressure issue. Will advise once I get the bottom end apart.

I would really like to know what you see in the bottom end. I am not sure if there is a pressure relief on these pumps or not. I was also thinking suction O ring, as oil pressure is good cold and once to operating temp it fluctuates with the RPM. Or just the pump is weak? I am guessing this is a gear pump, if it is I would think if it was going to bypass it would do it all of the time?

 

[BOBDOUGIE]

I would really like to know what you see in the bottom end. I am not sure if there is a pressure relief on these pumps or not. I was also thinking suction O ring, as oil pressure is good cold and once to operating temp it fluctuates with the RPM. Or just the pump is weak? I am guessing this is a gear pump, if it is I would think if it was going to bypass it would do it all of the time?

In searching google I am seeing that I need to cut my exhaust to remove the oil pan? I am guessing find a splice and U clamps to put it back together?

 

[BOBDOUGIE]

188K. I noticed when I put it on the rack that the sensor had oil on the bottom of the connection like oil was leaking through it. I am going to go ahead and change it before I go after the pump.

Bobdougie

I can only share my experience with this issue but if you google you will find a lot of similar stories. I have a '99 with 90K Miles. Oil pressure sits about 21 psi when warming up or under gentle load. When hot and you come to a stop the indicated pressure drops to zero and check gauge light came on. I swapped pressure sender transducer and no change. A manual gauge showed similar results.

I know the later model TJ's have a "Dumb" sensor but that's not what is happening here. I built a new engine and installed it over Xmas. Oil pressure hasn't dropped below 40psi since and usually sits about 50psi. Tried both original sender and replacement and same same so it wasn't an instrumentation issue.

I'm going to pull the bottom end off the original motor to see if there is any clue as to the reason in the bearings - noting the engine itself ran perfectly and pulled like a bus load of Catholic schoolboys so whatever the issue is it didn't seem to be manifesting (yet) in the motor itself.

<EDIT> I built the new motor on a different block for fun, not because of the oil pressure issue. Will advise once I get the bottom end apart.

Any luck on the bottom end of the old engine yet?

 

[JKP]

The oil pump pressure relief is 75PSI.

Min pressure at idle is 13 PSI per the FSM.

 

[ColoJeep]

188K. I noticed when I put it on the rack that the sensor had oil on the bottom of the connection like oil was leaking through it. I am going to go ahead and change it before I go after the pump.

Bobdougie


Any luck on the bottom end of the old engine yet?

What weight motor oil are you using ? Hot thin oil= low pressure at idle.

 

[BOBDOUGIE]

Castrol GTX 5W-30, with 400 miles on the oil with no issues. I turned in a sample today to see if anything is going on.

 

[ColoJeep]

Castrol GTX 5W-30, with 400 miles on the oil with no issues. I turned in a sample today to see if anything is going on.

Just curious , why 5W-30 in AZ. when 10W-30 is the norm ?

 

[DuckNut]

A while ago i watched a video on YT about this. I believe it was called there did the oil pressure go...or something similar.

 

[Bammo68]

A while ago i watched a video on YT about this. I believe it was called there did the oil pressure go...or something similar.

Yeah - someone here with more experience than me may chime in so happy to be proved wrong but I think a lot of people's concerns with oil pressure in 4.0's might not be grounded in an actual issue. Sometimes you just need to send-it and sometimes you need to stop and carefully evaluate the situation. You hear LOT'S of stories about this type of intermittent oil pressure loss when hot, when coming to an idle.

You know what you don't ever hear? Stories about how the 4.0 threw a rod after the oil pressure dropped one day - its a very, very reliable engine and there doesn't seem to be a strong correlation between low oil pressure indicators and seized engines.

Fresh oil change and keep an eye on it would be my thought.

 

[DuckNut]

Yeah - someone here with more experience than me may chime in so happy to be proved wrong but I think a lot of people's concerns with oil pressure in 4.0's might not be grounded in an actual issue. Sometimes you just need to send-it and sometimes you need to stop and carefully evaluate the situation. You hear LOT'S of stories about this type of intermittent oil pressure loss when hot, when coming to an idle.

You know what you don't ever hear? Stories about how the 4.0 threw a rod after the oil pressure dropped one day - its a very, very reliable engine and there doesn't seem to be a strong correlation between low oil pressure indicators and seized engines.

Fresh oil change and keep an eye on it would be my thought.

Our oil pumps are mechanical. A couple gears rotating in a meshing fashion to move the oil is about as fail proof as it gets.

A lot of the issues are self inflicted. These are not precision instruments but 1 step away from a tractor engine.

I have seen an onslaught of questions recently that are so bizarre that I scratch my head in disbelief that the question even was asked. Sometimes I would like to say sell it and buy a Schwinn because you are too dumb to own a car, but I don't.

Keep the fuel, oil and coolant systems clean and it will last another 25 years (unless rust devours it beforehand). I am by no means an expert but I do possess a little bit of mechanical understanding.

 

[5TTTj]

Yeah - someone here with more experience than me may chime in so happy to be proved wrong but I think a lot of people's concerns with oil pressure in 4.0's might not be grounded in an actual issue. Sometimes you just need to send-it and sometimes you need to stop and carefully evaluate the situation. You hear LOT'S of stories about this type of intermittent oil pressure loss when hot, when coming to an idle.

You know what you don't ever hear? Stories about how the 4.0 threw a rod after the oil pressure dropped one day - its a very, very reliable engine and there doesn't seem to be a strong correlation between low oil pressure indicators and seized engines.

Fresh oil change and keep an eye on it would be my thought.

I think that's good advice, but I always get nervous when I see low oil pressure and I know I shouldn't .

I purchased an old Ford truck that wasn't taken care orby the PO. I started using it on the highway and after the second trip ( 200 miles from home ) I noticed the oil pressure around 20 psi accelerating and at highway speeds, 0 at an idle. the motor never rattled or knocked so I thought it was a faulty sender. I drove it home on the interstate with zero pressure by the time i got off the interstate. When I got home i installed a mechanical gauge and guess what ???
I had very little oil pressure. I pulled the pan and found the oil pump pickup below 1" of sludge on the bottom of the pan. cleaned out the pan, installed a new pump, pickup and oil pump drive and I'm back to 65psi cold and 40psi hot. I'll be driving it this morning.

 

[BOBDOUGIE]

I think that's good advice, but I always get nervous when I see low oil pressure and I know I shouldn't .

I purchased an old Ford truck that wasn't taken care orby the PO. I started using it on the highway and after the second trip ( 200 miles from home ) I noticed the oil pressure around 20 psi accelerating and at highway speeds, 0 at an idle. the motor never rattled or knocked so I thought it was a faulty sender. I drove it home on the interstate with zero pressure by the time i got off the interstate. When I got home i installed a mechanical gauge and guess what ???
I had very little oil pressure. I pulled the pan and found the oil pump pickup below 1" of sludge on the bottom of the pan. cleaned out the pan, installed a new pump, pickup and oil pump drive and I'm back to 65psi cold and 40psi hot. I'll be driving it this morning.

Pulled the pump yesterday, Did not see anything obvious. Pan was clean, nothing in the screen, very clean. Filled the pump with oil and held the drive shaft withe a screw driver so its would not spin. Did some testing on the relief and it seemed like it was leaking by all of the time, and using air pressure as low as 5 PSI. The piston looked good, the spring looked good. Put a bore scope in the bore of the relief. Did not see anything obvious in that seat. The only thing I was. Concerned with was the area between the suction and the pressure port seemed pretty thin and could possibly crack? Will pick up the new pump today and do the same testing to it, to confirm what I found. I will let you all know.

 

[BOBDOUGIE]

Well I tested the new oil pump the same way I tested the old pump. The pump held to 20 psi then started leaking by. Put the TJ back together. Went for a test drive, got up to operating temp. The lowest pressure at idle was 20 PSI at 500 rpm (45 psi going down the rd). So I think I figured it out. Of course the idiot gauge in the dash didn't change. If you look at the pic below you can see how I tested it. When you put air pressure to the pressure side of the pump (After putting oil in the pump) and hold the shaft. You can look down inside the relief port and see it bleed by. It was actually pretty easy to test. I did notice in my last thread that I said that the the land between the suction and the pressure ports was thin. But it is actually the suction and the relief ports that are parallel to each other that is really thin. Thanks for everyones input on this.

Bobdougie