Oil Pressure Issue

[Capngeo]

Before I get everyone excited this is in my TJ, NOT the JT!!!

This is my dedicated trail jeep, a 97 TJ (Wrangler) with a 4.0 six in it. Suddenly on the trail yesterday (lots of water on the trail) she suddenly lost oil pressure on the gauge (mechanical aftermarket) but the engine didn't should like a "dry engine". Engine coolant temp was a bit high (210F), but thats typical for long pulls in low range. I actually saw the needle drop from 20 to almost zero. Shut it down as soon as I got out of the hole.

Oil level fine. no valve lifter tick, no knocks. I was 10 miles away from the trailer, and I'd rather blow an engine than walk that far through deep mud and water, so I ran it. Got to the (sorta) hard road and ran about 3 miles at 30mph. temp dropped to 180° and oil came back to 20-30# depending on rpm.

Got back to the shop, checked pressure gauge (accurate), thermostat (180 full open), coolant level (full), fan operational, radiator clear. I drove all over the ranch and couldn't duplicate the issue... BUT there was no deep mud here.

My mind is dancing around a lot of maybes, but I thought I'd bounce it off the brain-trust here. The engine is a fresh top end overhaul with cam about 5k miles ago, with zero issues before yesterday. Please save me from pulling the engine and tearing it down to look for an internal leak!

Sponsored

 

[agoldxj]

My 99xj 4.0 did this from 40k miles up to 220k when I sold it to my sister. Still did it to almost 300k when she traded it in. It would show 40-50 cold then when warm it would fluctuate between 0-30. Multiple sensors both Oem and aftermarket didn’t help. No noises no leaks no loss of performance. My 97 TJ 4.0 5 speed did the same thing but never went to zero, it was like 10-30.

 

[DylanM]

My bet would be on a small bit of crud temporarily blocked off the port to the pressure gauge and has now moved along, hopefully to the end of the tappet gallery.

 

[46flattie]

possibly a sticky plunger or piece of crud held the pressure relief valve open in the oil pump?

Also, what are you running for an oil filter? I had an oil pressure issue with the new non-Wix Napa Gold Chinese oil filters on my AMC 401 . (bought it not knowing WIx no longer supplies Napa).
Spun it off and replaced with a Wix and no more problems. All I can figure is the filter media was not flowing enough oil causing my pressure drop. I inspected the filter and could find nothing wrong with it, actually seemed pretty beefy.

 

[Capngeo]

My bet would be on a small bit of crud temporarily blocked off the port to the pressure gauge and has now moved along, hopefully to the end of the tappet gallery.

I had that thought as well, thanks!

possibly a sticky plunger or piece of crud held the pressure relief valve open in the oil pump?

Also, what are you running for an oil filter? I had an oil pressure issue with the new non-Wix Napa Gold Chinese oil filters on my AMC 401 . (bought it not knowing WIx no longer supplies Napa).
Spun it off and replaced with a Wix and no more problems. All I can figure is the filter media was not flowing enough oil causing my pressure drop. I inspected the filter and could find nothing wrong with it, actually seemed pretty beefy.

I bought a WIX to replace the POS Fram filter! Thanks!

 

[Jteakus]

Elec sending unit gauge or tubing?

 

[Capngeo]

Elec sending unit gauge or tubing?

Mechanical

 

[Capngeo]

So far, this is whats been eliminated from possibility: Gauge is confirmed to be accurate, no EXTERNAL leaks, tubing not blocked or kinked, pulled the distributor and ran the pump with a drill; pressure was normal. Waiting on oil filter delivery to confirm filter is not bypassing. Radiator fins clear, water pump in spec, coolant level good

What I am coming up with is thinking its heat related:
1] I changed the oil when I got the Jeep; I used a modern 5w-30 (too thin for a '97) going to change to 15-40 dino oil
2] Removed the oem crap fan and installed an electric (Thanks Eddy Baez)
3] Changed t'stat to 160°

Soon as I have time to work on all that I'll run it back to the Estates because I can't get it to run hot here on the ranch (no mud)... I'll let y'all know

 

[DylanM]

I think you're on the wrong track. Heat's effect won't make the oil pressure drop suddenly, it causes a gradual loss in pressure.

Engine coolant temp of 210°F is the factory normal operating temp for a TJ. It's not high, nor of any concern. If anything, running at 180°F is too low and tells me you have the wrong thermostat installed or it's faulty (should be a 195° stat).

The factory spec'd oil for your TJ is 10w-30 or 5w-30 and there's nothing wrong with using modern or synthetic. Full synthetic 10w-30 is what I've been running in both my TJ and LJ for a combined total of over 350,000 miles with zero problems. The weight of oil you were running isn't too low unless the bottom end of your engine is worn. For a reference to gauge whether that is the case or not, the 4.0L when fully up to temp should have a minimum idle oil pressure of 13psi. Normal oil pressure from 1600rpm to redline in a healthy engine should fall within a 37-75psi range (75psi is the pump's relief pressure).

I won't get into the whole OEM vs electric fan argument, all I will say is it has been tried a lot of times by a lot of different people in the TJ and the majority ended up going back to the OEM.

 

[Capngeo]

I should have mentioned this is not a daily driver; it’s a dedicated mud jeep, which is set up for deep water……

I have trouble with the heat too, but the only time I can replicate the issue is above 200°. This is about as far from stock as can be, it’s been switched up to carburetor, HEI ignition, headers /intake, cam, ported head. There is zero OEM computers/ electronics/ controls. About 50k on the bottom, 5k on the top.

Incidentally, the low oil pressure came right after an oil change… I wonder if I got some mislabeled lighter weight than the 20/50 I usually use??

The fan conversion has been long on the wish list as I like the idea of being able to turn it off with a switch.

 

[46flattie]

Incidentally, the low oil pressure came right after an oil change… I wonder if I got some mislabeled lighter weight than the 20/50 I usually use??

As in 20w-50? I run Valvoline 20w-50 VR1 in my 401 during the summer and my issue was right after an oil change too. That's what led me to the filter. (After checking the oil pump relief valve and finding it to be clean and the spring good...on the amc v8 they are external). My issue was primary when the oil was cold, pressure would drop with an increase in RPM. Once the oil was up to operating temp, pressure was more normal, but a little lower than normal. As mentioned above, once I replaced the filter with a real Wix, all was back to normal.

Interesting....hope the filter change helps.

 

[Jteakus]

I run Rotella 15w40 in my AMC 360.

 

[Capngeo]

As in 20w-50? I run Valvoline 20w-50 VR1 in my 401 during the summer and my issue was right after an oil change too. That's what led me to the filter. (After checking the oil pump relief valve and finding it to be clean and the spring good...on the amc v8 they are external). My issue was primary when the oil was cold, pressure would drop with an increase in RPM. Once the oil was up to operating temp, pressure was more normal, but a little lower than normal. As mentioned above, once I replaced the filter with a real Wix, all was back to normal.

Interesting....hope the filter change helps.

That was a brain fart... I was looking at an ad for 20-50 and typed that. I meant 15-40. Amazon was suposed to have the filter here today... now they are saying monday; I guess I'm off to town tomorrow

I run Rotella 15w40 in my AMC 360.

I had a 304 in a CJ7... thats what it drank. I run rotella in everything here on the ranch mostly T6 & MV.

I got the fan all in today wired it with both a temp switch in the head and a DPDT toggle. Now I can leave it in "auto" and it will cut in and out as temp requires, or constant on, or off (for the really deep water)

 

[Jteakus]

That's how I ran mine on my mud Jeep.

 

[Capngeo]

After all that wrenching, I'm still at 210° and 3 psi at idle. I'll get 30-40 psi at higher rpms, which is an improvement no doubt, as I never saw over 15 before.

I suspect the 210° is actually higher because the temp sending point is on the radiator side of the T-Stat instead of the head side. If I shut off the engine at that temp it struggles to turn over.

Bigger radiator? More cfms on the fan? I've got to cool this peckerwood down IMHO

Sponsored