Question95 JGC 4.0L 146,000 miles. Had 5W-30 in it, would start with 50 lbs of oil pressure, but drop to about 20 as temp increased. OK at highway speeds, slow, long uphill caused pressure drop to 10 and coolant temp to go from 190 to just over 210. Small oil leak possibly from pan gasket but has been there over 1 yr without problem. No oil consumption to speak of. Sending unit failure? Oil pump? My mechanic seems to think it's normal mechanical wear and increased tolerances with decreased pressure. Suggested heavier oil as bandaid treatment before rebuild. Any suggestions?
AnswerHello Andy,
Just did a follow up on all of my answers and noticed I had recomended using 5W-30 oil instead of 10W-30 at some point in my answer to your question. I meant 10W-30. Good luck with the JEEP! --Jeep4x4man
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Hello Andy,
First off, the oil pressure drop, and coolant rise is a common problem reported by Jeep owners, so for a older 4.0 it is starting to sound normal. However, continued operation like that, can cause excessive wear and break down of lubricants and engine/transmission parts. Thicker oil is not the cure, I can say this first hand, as I tried it once, and all it did was cause loud ticking from the hydraulic lifters, and more heat. Jeep recommends using 10W-30 oil in the 4.0, anytime the outside temps are 0 to 100F. I have had the best success with 10W-30 in my 4.0's. As far as the oil leak, it is a very common problem, to the point of a bumper stick that has come out about it. About a year ago I experimented on nearly every oil leak stop treatments, and found that CD-2 Heavy Duty oil stop leak works excellent. Again, it is a band-aid type of treatment, but it is helpful. I would have to say that the coolant's rise in temperatures is directly related to the low oil pressure, and not another problem of it's own. Before removing and replacing parts, I would try 6 quarts of 5W-30 oil and a new filter, such as the NAPA Gold, or WIX. These filters work well with the Jeeps. As I'm sure you've noticed, when you first change the oil, the pressure is good, but a week later it isn't quite so good. This is due to the oil breaking down or thinning, and it happens often on high mileage 4.0 engines. If the oil pressure problem isn't cured, have a mechanic just hook up a pressure tester to the oil flow and see what exactly the pump is putting out, in case the gauge and sending unit are faulty. If the pressure is low, try a bottle of STP oil treatment, in the blue bottle, this is a thick treatment, but is better than using thicker oil. If the oil pressure goes up with this, then it is a sure indicator of worn parts, including possibly the pump. I hope this helps you. Let me know if you have any other questions. Good luck with the Jeep! --Jeep4x4man
