Alright I posted a bit ago about the problems I was having and I still haven’t figured it out so any advice is appreciated.

I have a 2001 Cherokee with ~106k miles and have recently put in a new radiator and spark plugs.

My oil pressure gauge has been dropping after around 10-15 minutes of driving and then jumping up to ~20 while accelerating, then back down to 0 at idle. I thought this might have been a fuel pump or sensor issue so I replaced both just this week to no success. A mechanic recently advised me to get a transmission fluid change as it was brown but I don’t think that would be related right? I’m going to try some injector cleaner for good measure too but I’m just not sure where to look next, was really hoping the fuel pump was going to solve it.

Strangely, the car was taking longer to turn over before the fuel pump replacement and then immediately after the new pump it has started fairly quickly again but the gauge still drops as stated above.

What else could this be???!

Fuel pressure would not affect the oil pressure. I would try with a new oil pressure sender.

I replaced the little oil pressure sensor above the the filter, is there another part I need to replace?

This answer should be a sticky for 2000 &2001 my
1) put a mechanical oil pressure gauge on it and see what the oil pressure actually is. Stop messing with sensors


2) if , with the mechanical gauge, you get the sort of numbers you are getting now Google jeep 331 cylinder head. Look for the crack.

The numbers you are getting now are typical of an engine with bearings trashed by coolant getting into the oil

Edit: I looked at your earlier post and you said you were loosing coolant and people suggested checking with a mechanical gauge and mentioned the 331 head. Probably time to actually do some of what was suggested back thene

What @exasemech said. Also check your oil to see if it's milky (another sign of coolant in the oil).

Okay so I have been dealing with unexplained missing coolant, this is pretty certain for the 331 crack then? I asked the mechanic to look for this and they said it would be more catastrophic if it was cracked. But it’s looking like this may be the case, what does this mean long term? Only way to fix it is engine replacement?

If it is caught early enough, a new cylinder head will fix it. If it is ignored and allowed to become "more catastrophic" as your mechanic stated, then yes a new engine is the only repair.

Coolant doesn't mysteriously disappear. If there is no puddle under your Jeep, there is really only one other place it can go and that's the engine.

The head on my 2000 was replaced 150k miles ago and I'm still going strong, however the coolant loss was dealt with immediately.

Ah alright, thank you, I’m curious how much the cylinder head ran you and if it is worth the price rather than another option?

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it's pretty obvious you don't want to think about replacing the engine but put a mechanical gauge on it before you throw any more money at it. If the pressure is really 0 at idle and 20 max the engine is toast
And to address any possible confusion, replacing the head will do nothing to improve the existing oil pressure.

Alright the mechanical gauge reads around 8 at idle when the meter in the car just drops to zero. I also took off the oil cap and looked inside and didn’t see any gunk or signs of coolant or any obvious cracks but I attached two pictures just in case. My mechanics are saying it’s showing good signs of life even after I talked to them about the 331 head but I don’t know, I'm obviously pretty suspicious about the missing coolant and the pressure drops.

The next step if you're interested in finding out what's happening would be getting an oil analysis to see if there's coolant in the oil.
that would settle it

That is a great suggestion, and will stop all the guess work. I have used Blackstone in the past.

To answer the earlier question of how much it costs, I have no clue. it was well over a decade ago and I just can't even begin to remember. It was replaced with a TUPY head.

The fact that your dash gauge and the mechanical gauge are giving different readings give me some hope your engine can be saved, but you really need to stop driving it except to get the engine hot enough to take an oil sample. In the event your head is cracked, the longer you drive it the greater the odds of needing an engine vs a cylinder head.

Just throwing this out there on the oil pressure. My 2001 in past life (before me) must of had the dreaded cracked head. Can tell head has been removed before and believe cam bearing are worn due to my low oil pressure at idle verified with a mechanical gage. I got mine at 114k now has 156k idles hot at 10 psi and down the road doing 65 around 40 psi. I run 15w40 motor has the usual chatter but runs good and looses no coolant and I don't think it's gonna die anytime soon and plan on keep running it like this. When it goes then I'll do something.