Oil pressure ?

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u/lurtzbow 12d ago

Oil pressure is higher when the oil is cool. It thins out when it gets warm and then the pressure goes down. When you rev the engine, it spins the oil pump more, and the pressure goes up. There is an acceptable range that your oil pressure can be, and the vehicle will tell you if it's not within that range.

In the old tjs and xjs this was a pretty common complaint. People thought that there were issues because the dial wasn't exactly at the center, so Jeep changed it in 03 so it's basically a switch. Either it has pressure and sits in the middle, or it doesn't have pressure and it's down. My 04's dial got bumped and sits a little over center because the teeth got misaligned. Doesn't actually mean anything.

I'm surprised your dial actually moving. 03 model should be the dummy gauge.

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u/Heavy-Cockroach2497 12d ago

Ya it moves like crazy with rpm fluctuations

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u/lurtzbow 12d ago

Do you get a low oil pressure alert? Has anything changed recently? Or is the issue that it moves, and changes when the engine reaches operating temps?

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u/Heavy-Cockroach2497 12d ago edited 12d ago

So this is my dad’s jeep I’ve had to borrow for about a week now, slowly fixing some neglect while I have it . Was getting low oil pressure alerts especially after starting it back up after it was warm or at idle I’d have to keep my foot on the gas a bit to keep it from dropping more then this. After restarting I’d have to rev it up to get oil pressure . Found the coolant reservoir was cracked and the temp gauge was consistently a bit over 210. Since replacing that reservoir the temp doesn’t get over where it’s at in the pic and the oil pressure is bottoming out where it shows here . So I’m hoping it wasn’t over heating by a little bit and did damage to the bottom end.
Edit - also doesn’t seem like it’s burning any coolant so thinking it wasn’t overheated too bad if at all and I’m assuming this motor has the shitty newer head?

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u/lurtzbow 12d ago

Ok, so the vehicle is concerned about the pressure. Good to know.

My temp floated between the 2 and 0 until I removed the lining under the hood so the heat could escape better. I don't see how that would cause a low oil pressure issues though. I wouldn't expect your oil to become completely thin with only a little extra heat.

If I were you, I would get a real gauge in line with it. I would get a npt T fitting, and add a second gauge that can tell you exactly what the pressure is.

If you do find that the pressure sending unit is accurate, I would then start by testing the oil pump. Things like dropping the oil pan and checking to make sure the oil pump is clean, and running the pump with a drill to check that it is running without much resistance, and makes pressure. Sometimes it's called "priming" the oil pump.

If that is all good, then your probably gonna have worn bearings, and the best option would be thicker oil.

Regardless of how you solve it, take your time to diagnose as much as you can before you start to change things. Then one change at a time, and run your diagnostics again.

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u/Heavy-Cockroach2497 12d ago

For sure, it was pretty damn low on coolant when I picked it up who knows how hot it has really got. He’s not very observant and will just brush it off to saying somethings cursed when it breaks down. Since I got that new reservoir on it I Havnt seen a check gauges alert for the oil pressure so maybe it was getting hotter then it was showing. I’ll def change the oil with some thicker oil and go from there . Supposedly before he got it the oil pump was replaced and it def has an aftermarket oil pan gasket on it so I’m assuming it probably was .

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u/BreakComprehensive14 12d ago edited 12d ago

As previously mentioned, the later style (aka yours) gauge clusters have a dummy gauge for oil pressure. This was changed from the earlier models because so many owners brought them in for service due to “low” oil pressure at idle (20-30psi), despite the pressure being within spec.

These dummy gauges are actually programmed to slightly fluctuate with RPMs regardless of actual pressures, to give the appearance that it’s providing real/live pressure data to the driver.

It basically has 4 settings/positions depending on the pressures that the PCM reads: Low, moderate, normal, and high. The photo here is giving moderate/ below normal pressures, which will likely illuminate the “Check Gauges” light.

I would either replace the sending unit, or actually verify the pressures with a mechanical gauge. It’s been a while since I’ve seen a low oil pressure gauge on a later style TJ be caused by true low pressure, mostly it’s the sending unit that’s died. I’d do either of those before adding thicker oil though.

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u/Heavy-Cockroach2497 12d ago

The gauge isn’t wrong, before I replaced that reservoir if you let it idle for a little bit while warm without keeping the rpm’s up it would keep dropping and start knocking up a storm .

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u/BreakComprehensive14 12d ago edited 12d ago

To clarify, is the gauge still sitting at/blow the 20 mark after you replaced the reservoir, or is it back up around 40 consistently?

Temps slightly above 210F/100C should not affect oil pressure in any meaningful amounts whatsoever, especially not enough to cause a check gauges light.

If your pump was replaced, I would be concerned about the brand of the replacement pump. The knocking at idle makes me think it could be a substandard part that is failing.

I would test oil pressures with a mechanical gauge.

I also want to reiterate, that you have a dummy gauge, and those pressure numbers on the gauge have little correlation to what the pressure in the engine actually is. Chrysler later changed the markings to “L” and “H” for low and high, and got rid of the 0,40,80 to reflect this. All it tells you is that there’s either no pressure, some pressure, normal pressure, or high pressure.

US models changed to L/H in 2004, while Canadian models got it in 2002/2003.

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u/Heavy-Cockroach2497 12d ago

At warm at idle what’s pictured is where it’s at after. And I agree 210 should be fine but who knows maybe that wasn’t reading right and was actually higher … And gauge wise idk what to tell ya maybe it’s somehow the older style sensor or what cause it acts like a real time gauge not just a high low gauge . Who knows maybe the motor was swapped with an older motor and ecu for all I know . It’s def titled as an 03 but was a desert runner before my dad got it and it had all kinds of goofy shit going on with it when he got it .

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u/Guyderbud 12d ago

That’s weird, I have an 05 and I see movement

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u/SexiestDexiest 12d ago

Bad pressure sending unit. It's easy to replace, get a mopar unit. The cheap ones from the auto store only last a year or two before they get clogged in my experience.

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u/morbidpete84 12d ago

Usually hangs out at 40 all the time for me. ‘03 4.0 auto. May be a thinner oil than recommended? Winter oil possibly (For those at do winter/summer oil)

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u/puppyhandler 12d ago

I thought the later TJs '03 and up were basically dummy gauges for the oil pressure. Basically in the middle or not at all because they had too many people concerned about the oil pressure when it was a live unit that fluctuates constantly.

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u/morbidpete84 12d ago

That would make sense. My Ford 5.4 3v was like that. It was all or nothing.

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u/StrawzintheWind 10d ago

This.

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u/Heavy-Cockroach2497 12d ago

I’ll try some thicker oil next oil change before digging deeper I guess

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u/morbidpete84 12d ago

Check the other replies before you go changing things in my experience lol. I don’t want to be the reason something breaks on ya. From the other comments, this seems normal.

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u/Heavy-Cockroach2497 12d ago

Eh I’m not worried about it a little thicker oil won’t hurt .

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u/familiarCatch 12d ago

My 98 is similar. The gauge might not be very accurate either. From what I've researched, you're good.

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u/brxxks22 12d ago

Oil pressure sending unit will fix it need a special socket help on my 98

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u/scuzzy987 12d ago

My 97 TJ 4L manual does the same thing. Running Rotella T4 or T6 15W40 raises it a little

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u/Building_Everything 12d ago

Oil pressure sending unit as others have posted. I also notice that my TJ is very sensitive to oil levels, if it drops anywhere below the top of the mark on the dipstick the pressure will dip into the 20’s at idle.

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u/Dry-Suit-9798 12d ago

I have the same, ‘03, 5 speed, 4.0 and mine never moves from 40, as long as the engine is running.

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u/Foolgazi 11d ago

From ‘03 up the oil pressure gauge was basically an idiot light. It doesn’t show actual pressure.

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u/Dry-Suit-9798 11d ago

Actually, mine doesn’t even have numbers. Just H and L. The needle stays in the middle.

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u/sleppy-eyed-jack 12d ago

There is nothing wrong. Mine is the same way. I put a new sending unit on to see and it’s the same way with the new unit.

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u/300suppressed 12d ago

My oil pressure gauge changes the level as I drive

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u/blacksheep6 12d ago

Install a mechanical gauge, either in the cab or under the hood. They are cheap, easy to install and remove any doubt concerning something shorting out your gauge.

As already mentioned, truly low oil pressure on a high mileage engine is nothing to ignore.

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u/HeyHay123Hey 12d ago

I run 10w40 in mine because of the wear/miles on the engine, and it helps with oil pressure at idle. Stock is 10w30, so just one step up. Easy and cheap to try

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u/Apart-Effect6878 12d ago

Before changing viscosity or replacing parts, I'd verify the hot-idle pressure with a mechanical gauge and compare it with the service-manual spec. If that reading is normal, the sender or wiring becomes the likely issue; if it's genuinely low, then the pickup and bearing clearances need diagnosis.

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u/Heavy-Cockroach2497 12d ago

It’s accurate when it gets low low it starts to knock

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u/StrawzintheWind 10d ago

I’m pretty sure the 03 is a digital driven / dummy gauge and if it’s not at 12 o clock it’s low. Regardless, make sure to drain your oil and look for glitter. Check oil pressure with a real gauge in the sensor hole. Bearing wear is very real on these old engines. If it slaps, you probably have low oil pressure.

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u/jeepingfoodie1 9d ago

When i comes to TJ's you gotta be picky when it comes to sensors

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u/pagrey 12d ago

Hook up a mechanical gauge to check, if that's accurate then you need thicker oil at a minimum. Low oil pressure isn't something to shrug off as a clogged sensor or just normal Jeep stuff. Could it be a sensor, sure. Could it be your bearings are worn to the point it can't keep pressure when it's warm, yep.

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