Scary start-up noise-again....

[CJS]

I finally got around to pulling my oil pan (90' 4.0 non-HO , aw4, etc.) and realized when they changed the rear main they didn't clean the pan as it was full of sludge. I cleaned the pan out and now have good oil pressure (25 psi at idle fully warmed up). The only problem is when I go to start the jeep after it fires for 1-2 seconds the motor still sounds as if there is no oil in it. If anybody could enlighten me it would be great. Basically it only lasts 1-2 seconds when the motor first fires and run at fairly high rpms. I'm not sure what else would make the sound, it has to be the motor (could a bad water pump sound that bad??).

[Hawaiian Style]

How many miles? My 4.0 sounded like that before I had it rebuilt. Kind of a grinding/clanking unhappy noise. The verdict in my case was the engine was shot. Don't want to scare you but it only happened for a couple of seconds after start and when it was under a higher load... I'd get it checked out by a good shop.

Good luck

[old88xj]

I agree with Hawaiian....sounds like that bc a bearing is not getting any oil and is running dry IMHO....had the same sound and turned out to be a rod bearing spun, along with a main bearing and scarred crank..no fun...gonna buy a new motor and install it

[Hawaiian Style]

I've heard this problem described as "the bottom end getting hung up". I describe it as a rebuild. Oh well, when I got the Chief done it was amazing the kind of power a "new" 4.0 has. Best of luck to you...

[CheapXJ]

what kind of oil filter are you using?

depending on the filter, it may not have the proper anti-drainback valve in it.

Mine would do that the ONE time I used a fram filter. switched to purolator... problem solved

[CJS]

I'll try changing the oil filter. I just have a hard time believing the bottom end is junk, it runs awesome just sounds bad on start-up.

[Hawaiian Style]

Perc. filter? Aren't those no better than Jiffy Lube filters? I've been running Frams for years with absolutely no problems.

As for the bottom end thing, that was the deal with mine under same conditions. Hopefully not for you. Have a requtable engine shop take a look at it.

[Neil]

Try running synthetic oil you can get viscositys from 5w to 50w I have 227345 on my rig and I run 5w 50 synthetic. No noise great oil pressure cold and hot, best of all no sludge. Try not to rev the engine during the first 2 minutes of operation, it does take a little time for oil pressure to build up.

[CheapXJ]

Originally posted by Hawaiian Style
I've been running Frams for years with absolutely no problems.

As for the bottom end thing, that was the deal with mine under same conditions.

absolutely no problems :confused:

[Hawaiian Style]

I guess I'd better clarify that... I bought my Chief at 149k with an overheating problem and with the bottom end problem. I've had it for 2 years now with a fresh rebuild 4 months after purchase. No engine problems and Fram since rebuild. All my other cars since I was 16 have had Frams. None of them have had any engine trouble. Key to engine happiness is temp and oil (of course being nice to it and not flogging it too often helps).

[Jeep914x4]

This may be way off but my 91 cherokee was making a similar noise I thought meant I needed a rebuild or different oil filter. It turned out to be the four bolts holding on the flex plate. It was rattling around and making noise. Maybe a long shot but check it out.

[old88xj]

Jeep914....i have heard that also, it is a cheaper less time consuming thing to check and fix. Definitly worth checking

[XJEEPER04]

i cant believe nobody asked what oil he is running....if its too thick that maybe the problem...its a longshot but just trying to help

[Neil]

I sugested the 5w50, if he is running the 20w50 his engine can go for up to 2 minutes with no oil. The pressure will read fine but the oil is so thick at start up that it can't get into the small oil passages, like lifters and crank and cam berings. I know the synthetic is more expensive but the 5w50 is like water when cold, and on the hotest days (105) my oil pressure is still at 65-70 psi

[CJS]

I am running 10W30 castrol syntec (partial synthetic). Do you think 5W50 would help?? Probably couldn't hurt any.