[theducksguts]

I have been battling low, but acceptable oil pressure on my 2000 XJ. I have a couple questions. Hopefully collective knowledge will prevail.

1. It idles hot at around 13-15(sending unit replaced, no change)which I believe is acceptable, however, when idling hot, it sounds like their is a little Gnome trapped in my valve cover and he is knocking on it with one fist to get out. When I give it some gas, he gets tired of knocking and stops. Any ideas?

2. When starting hot the 4.0 will growl and rattle a bit until I give it some gas. Then it stops. What gives?

3. I would like to switch to full synthetic oil. Could you recommend some brands and viscosity that would help or a be a good match for my system? Or, what about switching to Rotella 15W-40?

I recently replaced the cylinder head after the original one cracked. I caught it early, cleaned out the engine.

It runs like a champ, gets 23 mpg on hwy trips. Just these lingering symptoms. Not such a huge deal. I am just a perfectionist.

[Chris_Walker]

How much oil pressure does it have at cruising speeds (1500-2000rpm)? 13-15psi at idle is where it should be when hot. Do you have a lot of sludge buildup in your engine that you know of? If you think it may be sludge or a partially clogged oil passageway, you could adding using Seafoam into your oil. I've always experienced good results with it.

[theducksguts]

Originally Posted by Chris_Walker

How much oil pressure does it have at cruising speeds (1500-2000rpm)? 13-15psi at idle is where it should be when hot. Do you have a lot of sludge buildup in your engine that you know of? If you think it may be sludge or a partially clogged oil passageway, you could adding using Seafoam into your oil. I've always experienced good results with it.

Thanks for the tip. When driving normally/non HWY it runs at about 35 so it's in pretty good shape there. Someone else I spoke to mentioned Restore engine treatment. Anyone know about that?

[Chris_Walker]

Your oil pressure is fine then. You probably just have a small blockage not letting enough oil get to one or two of the rocker arms. I highly recommend Seafoam. I've used it on all my cars, family, and friend's cars. A few of them had really terrible valve train noises, and within about 20 minutes after adding Seafoam the noises stopped completely. When I worked at Autozone, people I've recommended it to came back to me with good results. I know a lot of people on this forum swear by it. I don't have any experience with Restore though.

[theducksguts]

Anyone have comments on Synthetic oil vs. 15W40 Rotella?

[Chris_Walker]

You don't wan't to use Rotella unless your having problems like me. In the summer time it might be okay, but in the winter, it's too thick and you can blow out seals or cause engine damage. I'm running it because I have a worn oil pump that I haven't got around to replacing yet. With 10W-30 I would get 0 oil pressure at idle when hot, and about 15 under load. With Rotella it's back to normal. However, on cold days, I can't drive it until the engine warms up. The Rotella is too thick and when cold it causes the oil pressure to spike around 70psi. It also rattles like a diesel until it warms up.

If you want to run synthetic, here's my recommendation for next oil change:

6 Quarts Mobil 1 High-Mileage Synthetic (Mobil 1 HM has ZDDP in it)
1 Can Seafoam
Mobil 1, Bosch, or Mopar filter.

If you run something other than Mobil 1 HM, pick up a bottle of STP Oil Treatment, it contains ZDDP, which is necessary for metal-to-metal lubrication on flat tappet engines like the 4.0L. Most oils used to have it up until a few years ago when it was removed for environmental reasons.

If you don't want to spend that much money on Synthetic, there's good synthetic blends like Kendall, and Motorcraft oils.

[theducksguts]

Originally Posted by Chris_Walker

You don't wan't to use Rotella unless your having problems like me. In the summer time it might be okay, but in the winter, it's too thick and you can blow out seals or cause engine damage. I'm running it because I have a worn oil pump that I haven't got around to replacing yet. With 10W-30 I would get 0 oil pressure at idle when hot, and about 15 under load. With Rotella it's back to normal. However, on cold days, I can't drive it until the engine warms up. The Rotella is too thick and when cold it causes the oil pressure to spike around 70psi. It also rattles like a diesel until it warms up.

If you want to run synthetic, here's my recommendation for next oil change:

6 Quarts Mobil 1 High-Mileage Synthetic (Mobil 1 HM has ZDDP in it)
1 Can Seafoam
Mobil 1, Bosch, or Mopar filter.

If you run something other than Mobil 1 HM, pick up a bottle of STP Oil Treatment, it contains ZDDP, which is necessary for metal-to-metal lubrication on flat tappet engines like the 4.0L. Most oils used to have it up until a few years ago when it was removed for environmental reasons.

If you don't want to spend that much money on Synthetic, there's good synthetic blends like Kendall, and Motorcraft oils.

Synthetic W-30 or -40?

[Chris_Walker]

I ran Mobil 1 10W-30 in my XJ.

[jeepkid03]

I wouldn't run 15W-40 its too thick. My friend runs rotella T synthetic 5w-40 in his '89 XJ year round. Hes got about 260K on it now and it has great oil pressure. Its okay in winter because of the 5W rating when cold and the thicker 40 when hot. This means for cold starts it will be thin enough to get oil to the rockers, but when the engine is hot you will have better pressure. For my next change in about 800 miles i'm switching to this. My friend swears by it.

I would:
-add seafoam to old oil and run for 15 minutes in the driveway before changing
-change the oil with a good Wix, Napa Gold, Purolator or Mopar filter
-use the Rotella T synthetic 5W-40

If you still have that pesky little gnome in there after the change, then I would add some engine restore to each oil change after and see if it helps.

[nwautoxer]

Try Mobil 1 High Mileage 10W-40; I had significant improvement in hot OP under normal and heavy load conditions when I made the switch. Also, Jeep offers a high volume oil pump for the 4.0L which I would like to try in the future. All else being equal, a higher volume of oil is more desirable than a higher oil pressure.

[theducksguts]

Well I ran some seafoam in the oil, drained it and added 6 quarts of Mobil 10W-30 full synthetic with a Mobil 1 filter. Oil pressure is now lower than it was. It never drops below 13 which is fine, seems to be lubricating well. Am I just out of my mind over this? Is this really a big deal?

I did blow the head a couple months ago but everything tested out really well after I installed the new head. No issues what so ever. Main bearings seem fine. Cam bearings seem fine. It freaks me out because it runs so different than our 99. On the 99 it will vary between 30 and 40 the whole time. The 00 is just different I guess. Different head, different everything.

What do you think. Am I just over reacting?

[Wiskey]

I have a 91 with about 900 miles on an engine with brand new main and cap bearings,.. and my pressure varies between 19 or so, and 40.

I don't think you have anything to worry about at all, your not that much lower than me.
Whiskey

[the_weirdo]

I think it sounds like you have a typical XJ. I wouldn't worry about it.

[koolaid5]

I'm in the same boat with my '92 only I'm a little lower. I'm sitting at around 10psi and I get a bit of a knock at idle when the engine is warm and the rpm's are under 1000. Let me know if you come up with a fix for the pressure.

[koolaid5]

Originally Posted by the_weirdo

I think it sounds like you have a typical XJ. I wouldn't worry about it.

I disagree and I'm with the OP... I wouldn't worry about it if there was no engine noise with the low pressure, but the engine noise worries me