I just bought a jeep N the guy said he put in a slightly larger cam and a high flow oil pump. I'm reading 10psi on the stock dash gauge for every 1000 rmp... Ie 10psi at 1000, 20 OSI at 2000, etc... But it drops really low at idle and the check gauges light comes on. Would this have anything to do with the high flow pump? Or maybe that mixed with the stock gauges, Idk if they work together or not. The engine also has ample power, no knocks, idle is smooth, fluid levels good, doesn't overheating, and no smoke out the tail pipe. Also is a high flow pump bad or hard on a mostly stock engine.

 

Coming from a Hot Rod shop background, I have never been a big fan on High Pressure or High Volume oil pumps. A properly set up engine needs neither. That said, we did, and I still shim the pressure spring of the oil pump with a Holley Carb jet. Doing so gives you 5 to 7 PSI over stock, nothing major, but with that 1 tweak, a slightly worn engine is much more forgiving.

Get a manual gauge and check your pressure, or switch to 10w40 and see if that helps. Im betting your bottom end clearance is 2 to 3 thousandths too much. Probably no knock, but too much clearance for good oil pressure.

YMMV
Ron

 

Yea I'm affraid its worn out too and that's why I'm not getting the proper pressure, the engine only has 122,000 on it but maybe it just wore bad. I'm getting a gauge to hook up to the engine soon and changing the oil to full synthetic, maybe ill up the oil weight or maybe get a oem pump and put it in.

 

Is the engine using any coolant? You have an 01, which has the "infamous" 0331 cylinder head. This head can crack between cylinders 3-4, because of a casting defect.

If/when that happens, coolant mixes with the oil and if not caught quickly, can toast the bearings resulting in LOW oil pressure.

It is not that uncommon.

But as mentioned, you should always verify low oil pressure with a "mechanical" oil pressure gauge, which can be rented from many parts stores.

Good data = Good decisions.

 

I've only had it a few days but I haven't noticed a drop in coolant and the oil is nice and clean on the dipstick and not milky. I'll know more when I change the oil or maybe drop the pan. But ill keep the head in mind for sure, thanks.

 

I am considering an oil pump replacement also. Are you able to drop the pan without a hassle? 2wd.
Also, I tried synthetic in another high milage car and it was worse. In simple terms, The synthetic lubricates in a thinner manner. If you think the bearings are getting some clearance it may actually start to knock. I agree with the 10-40 regular.

 

I just checked the oil pressure with an external gauge and its reading only 16 psi at 1600 rpm, and 30 psi at 3000 rpm. I think I'm supposed to ne getting 37 psi at 1300 rpm. Guess ill have to keep looking into this. Hope the internals aren't completely worn if that's the problem.

 

Up the weight of the oil, it will buy you some time.

Ron

 

I recommend using a thicker weight motor oil also, to get a little more life out of those bearings. A good conventional 10w-40 or a Diesel 15w-40 might bring up that oil pressure a bit, probably not a whole lot, but the thicker oil film between moving parts will help them last longer. Jeep 4.0s like 40 weight oil anyways. Ive got a 2001 SilverStone Metallic with a low mileage 4.0, and Shes got Quaker State 10w-40 in her sump. If you are willing to spend $25 to get a oil analysis done, this would tell you if your bearings are shot, and if it was done by coolant in the oil, that would show that the head might have a crack between numbers 3 and 4 exhaust ports. If the crack has been around long enough to have coolant built up on it, you should be able to see it straight below the oil fill cap, on the exhaust side. Blackstone Labs is one of the best Oil Analysis companies around. They even send you the kit you need to send them a sample for free.

 

I put in a regular 10w40 and it brought the pressure up about 10 psi but not much of a change when hitting high rmp but over all I think its the way to go

 

I have a 2000 sport. I had the same low oil pressure at idle. When I bought it, the oil was clean, clean, clean. Too clean. The whole dang vehicle was clean. It also had a cracked head! I replaced the crank and rod bearings, new oil pump and put a clearwater head on it.
I walked into a bad deal, but with a little work, I made it right. Now my oil pressure is fine. Check to be sure you don't have coolant in your oil right away. It might not be too late to repair the damage without a huge hit your pocket book. Let me know.

Good luck.

Edit: Just reading your OP again. I wonder if he has the right bearings in? It does sound like tolerances are out.

 

This is interesting stuff to me. My buddy had a renix kee and I have a renix kee.they both read about 20 at idle. Mine hits 55 to 60 by 3000 rpms though.....sound normal? Most vehicles I've owned and worked on idle.around 30 to 40.... I don't worry about it too much because the pressure snaps right up as soon I rev. My buddy had a problem with his oil pressure going from 45 down to like 10 while driving after about.three hours.... anyone else have similar symptoms?

 

Sorry can't edit on the app... I was going to say I thought 20 was fairly normal at idle for these engines.... I actually have TWO friends with stock Cherokee that run around 20 at idle.

 

20 psi at hot idle is quite normal. My 99 has run there since the day I drove it off the lot 13 years ago.

Here is the oil pressure spec for the 4.0

*Not less than 13 psi at hot idle
*Between 37-75 over 1600 rpms

If you're in this area, you're fine.

 

The Peep runs 800 to 1000 miles weekly. When hot, after runnin 2hr or more, on beat up oil at midlife or end of life (4-5000mi) I see oil pressure drop at 500rpm idle to 20psi, 45 psi min at 50 mph or around 1500 rpm. When the oil is fresh hot pressure at idle is 25+ psi and 55+psi at speed (pressure is 60+ when cold). 10w30 name brand and fresh filter each time. 512000 km (31700+mi) on 89 Renix. Don't like to promote the snake oil additives out there but I have been watching results with the Lucas oil stabillizer (3/4 liter in the mix). Has consistantly added 5 to 10 psi thru the life of the oil on past 6 services. My current plan is to run the Lucas additive with the standard name brand oils rather than the hi-mi oil options. If you select to run 10-40 or 20-50 to get some pressure in a worn bearing situation, that won't hurt you.