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gregsredlaredo 08-22-2012 08:55 PM

1999 4.0 lifters and oil pressure
I bought an old 99 JGC Laredo with the 4.0 engine with 182,000 miles on it for something to keep me in the garage and out of the wife's way. I paid a bit less than what the market is getting for these old high mileage JGC,s so I expected some repairs. My wife has a 99 JGC Limited V8, I have a 97- 4.0 and now a 99- 4.0. So yeah, we like our Jeeps. .

When I test drove it, the engine had the same 4.0 "tick" my old 97 JGC has with a 150K miles on it, so I paid it no mind really. It ran strong, no smoke, so I was pleased with my shadetree mechanic engine inspection. :rolleyes:

Got it home and start doing my service cleanup on the Jeep. It had very black, dirty, thick oil in it when I drained it. Put in new 10w30 Valvoline conventional and Purolator Pure One oil filter. Started it up and now I have what sounds like a "diesel" engine in my Jeep.:lol: The lifter noise on start up is loud, but the noise does lessen a lot after accelerating and driving ...

I read on this and other forums that I should do a internal engine cleanup to clean up the lifters. So, I drained a qt. of the 10w30 out and added a quart of Mystery Marvel Oil. On a cold start, it sounded like the lifters were draining dry of oil while sitting overnight. So after some more forum reading, I switched the oil filter out to a NAPA Gold. Next morning on a cold start (75 deg F.) the lifters were not dry sounding any longer, but still noisey until accelerating...

Ran this setup for 200 miles and changed the oil out to 3 qts of Vavoline MaxLife 10w30 with two qts. of 20w50 VML and topped it out with a qt. of Risolene and another NAPA Gold filter. My oil pressure at idle has now went from 38 psi to 44. Is this normal ?....

I was thinking the oil pressure should drop as the engine cleaned itself up, is this right or wrong thinking ? What should normal oil pressure readings be for this engine ?

I realize the PO probaly put sawdust or 140 W gear oil in the engine just to sell a quieter engine, but I am persistent and would like to see if its worth trying to save. I can live with some of the typical 4.0 valvetrain noise, but not a diesel in a JGC. :o After running this Risolene treatment for 200 miles, my next and final effort is going to be a Seafoam job.. Once the cleanup is done, what brand oil/weight/ or additive would you recommend to put in this old engine ?

The rest of the Jeep is really nice and solid and I feel worth my efforts and the $$$ to try to save the engine, but I also realize it may be impossible to do without a new cam and lifters being installed . $$$$$$ ! ....

Not sure I would do that on a 182 K engine though without a total rebuild. Sorry about my first post being so windy. :sleepy: Thanks in advance for any additional info in helping to make my " diesel" engine sound like a gas engine again. :lol:

JeepMe 08-27-2012 08:06 PM

Re: 1999 4.0 lifters and oil pressure
I'm not sure what the oil pressure should be, but adding thicker oil will increase the pressure.

Have you considered pulling off the valve cover and checking out the condition of the lifters?

TheStreet16 08-27-2012 11:36 PM

Re: 1999 4.0 lifters and oil pressure
I have an '00 with a 4.0. My oil pressure sits at about 44 when I am running. Occasionally if the motor has been working hard or been running for 45 mins or longer, the pressure will drop down to about 38 while I idle. Once I accelerate, it will climb back up to 44.

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