Hello. I have a 2001 Wrangler with a 4.0. It has 112k miles. We purchased it for our son. Last spring it was having cooling issues, and discovered that it had a cracked head. We replaced it, all good. Recently, my son called me to say that it didn't have any oil pressure. Ugh. Reading some threads, decided to replace the oil pressure switch, and to clean the passage leading to it...no luck. Purchased a mechanical gauge, and corfirmed that while cold, pressure was good, but upon warming up, dropped to 6 to 8psi. Ugh. I don't want to face reality that the motor is probably toast, can someone offer any encourgement? If not, how about a decent used motor. I have the room to do a swap, although I have never done a jeep...any help would be appreciated. Thanks, Mark.
Bad motor?
- Thread starter Baydog
- Start date
Pumps don’t always just fail and crap out entirely. They can slowly start to go bad.
As mentioned, I did strain the oil and diasect the oil filter, and I did not see the metal that I expected to see if the bearings were toast.
Numbers vary with altitude and temp usually. More important is how the numbers compare.
If you’ve got most cylinders reading around 190 and one reading at 100, then you’ll have an obvious issue.
sgtjdgelinas
TJ Enthusiast
Oil is thicker when its cooler, once it heats up the space in worn oil pump gears would allow the more viscous oil to pass. That's why any hydraulic system needs to be tested at operating temp.
Thanks. I think that I have a compression gauge. Man, I really hope that it is it. I have read so many posts about others with the sender issue, but not many oil pump issues
Realistic compression numbers should be in the 130 to 160 range, but as Chris said, it is more important that they be fairly close together. Make sure you perform both wet and dry tests on each cylinder, that all plugs are out before you start and that the throttle is held wide open when cranking.
You got the answer, right? Cold oil is thicker, so as it warms up, a worn pump had a harder time generating the required pressure.
Regarding the compression test, does the crank case need to be filled with oil? I haven't refilled it since draining it and inspecting the filter.
Jeepaholic
TJ Enthusiast
Oil pressure and engine compression have nothing to do with each other. You can have good compression and bad oil pressure. A compression check will not verify a bad oil pump. If the engine isn't knocking yet, and you don't see metal, drop the pan and check for metal. If you find nothing, no fuzz at all, you could try changing the pump. Maybe you caught it before any real damage has been done
I don't know if I would crank the engine over for the compression test before you refill with oil,
Jeepaholic
TJ Enthusiast
I wouldn't bother compression testing it. If it ran fine and wasn't idling really rough, compression is usually good. If it wasn't running very good and had no oil pressure though, doesn't hurt to check it. Since it is drained, I'd replace the oil pump. You can comp check with no oil, not the best thing to do though, and I wouldn't do it myself with no oil.
I would do the pump first, even if you get a reman motor it might not come with it, it is not too expensive, I would then run the next batch of oil with seafoam in it, use a motor flush and redrain after a few hundred miles.....assuming it is not so low on oil pressure that you don't want to drive it....although at that point who cares anyway.
I have, on my first car. 1982 Cutlass Supreme with the 3.8L 6. There was nothing "supreme" about that engine. Anyway, the oil pressure was low, so my dad and I replaced it, bump the oil pressure up so much we found a bunch of oil leaks! It was kind of a crappy car, but I learned a LOT from it.
DISCLAIMER: I'm not a genius with engines, but this is how I've understood oil pressure. Oil pressure usually decreases as engines get older, which is where my intuition comes from when it comes to what I'm saying in this post.
Oil pressure usually doesn't have too much to do with the pump actually. What creates pressure is the clearances in the engine. This video explains that pretty well.
In summary, the flow restriction is what creates pressure (the restriction being the clearances in the engine). This why oil pressure is such a good indicator of engine wear. Whenever I've seen an engine with low oil pressure, the diagnoses is usually a worn engine, not a worn oil pump. At only 112k, I'm surprised your engine has such low oil pressure, but it could have had a bad life before you got it.
Changing an oil pump might do something, or might do nothing, but I don't think it will fix the issue in this situation. I've very rarely heard of oil pumps dying or wearing out. My 4.0 at 225k miles still has way over 40 pounds when cold and even when warm, depending on RPM.
Oil pressure usually doesn't have too much to do with the pump actually. What creates pressure is the clearances in the engine. This video explains that pretty well.
In summary, the flow restriction is what creates pressure (the restriction being the clearances in the engine). This why oil pressure is such a good indicator of engine wear. Whenever I've seen an engine with low oil pressure, the diagnoses is usually a worn engine, not a worn oil pump. At only 112k, I'm surprised your engine has such low oil pressure, but it could have had a bad life before you got it.
Changing an oil pump might do something, or might do nothing, but I don't think it will fix the issue in this situation. I've very rarely heard of oil pumps dying or wearing out. My 4.0 at 225k miles still has way over 40 pounds when cold and even when warm, depending on RPM.
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