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2000 jeep grand cherokee no oil pressure when warm

23K views 13 replies 5 participants last post by  Doug4230 
#1 · (Edited)
I just bought suv, at cold start engine has about 40 psi as engine warms psi drops to zero , i have changed oil pump, pressure sensor, put 20w50 in it changed filter, put mechanical pressure gauge on to confirm low pressure, everything looks clean when i had pan off, I STILL HAVE LOW OIL PRESSURE, TODAY I AM GOING TO TRY THE LUCAS OIL STABILIZER, any help would be greatly appreciated
 
#2 ·
if this is the 4.0l I6 they have a problem with a cam bearing walking out of the journal thus causing low oil pressure. there is no repair for this other than replacing the block due to the oversized journal... not sure what a machine shop could do for you if this is the case.
 
#4 ·
I could not tell you for sure but I will tell you that they walk out because of the journal is machined too big, so pushing it back in wont do anything for you
 
#5 ·
dropped the pan again today and looked at the cam bearings, i can see each one, they seem to all be in place, soooo to try to get the oil pressure up i replaced the pressure relief spring in the oil pump with a stiffer one, at first i tried 20w50 with one quart of lucas oil stabilizer, but after the engine reaches 180 degrees at idle the pressure drops low enough for check gages light to come on and alarm ding, i tried something thicker so i changed the oil to 85w140, but i still have the same problem, does anyone have any ideas for me to try next?
 
#8 ·
Drove the jeep to my sons house about 20 miles away today, cold the pressure was 60 psi as it warmed up during the trip it steadyly dropped, at a red light 20 mins into the drive the pressure finally dropped enough to cause the check gages light to come on and ding, after an hour at a resturant we headed home psi was about 30 psi so i decided to take the interstate home, 5 minutes on the interstate at 65 mph the pressure held at about halfway between 10 and 20 psi, as some as i stopped on the exit ramp pressure droppped to zero i pulled over, checked everything , every thing was fine, no noises, engine running smooth, i drove the last 6 miles to home at around 55 mph the oil pressure never raised above zero, when i got home i put the mechanical gauge back on, it also states zero oil pressure, i could see the oil in the oil line to the gauge, it wasn't moving, i revved the engine alittle and i could see the oil move slightly, but still zero pressure, still no engine noise, i removed the filler cap and looked inside, i could not see much, but i did not see oil splashing around but that does not mean anything like i said i could not see much, and i did not hear any lifter noises, or rockers tapping, everything seems to be running smooth and quite, so i thought maybe the port for the sending unit maybe blocked, so i removed the oil line and blew 150 psi of compressed air through the port, i put the mechanical gauge back on and no change zero pressure.
Does anyone know if there is another port that i could try the pressure gauge on????
 
#9 ·
Wow, I have the same problem. It was like this when I bought the Jeep six months ago.....I finally said to heck with it and just drive it. However mine does come up to about 20 psi at cruising speed. I can see oil circulating through the oil fill cap but it is very little unless I rev it above idle. I do plan on dropping the pan to look at the mains and cam. A bad main makes the most logical sense because there would not be any noise with just ONE bad main.
 
#11 ·
What kind of oil filter are you using? If it's a Fram, change it out and put in a quality Mopar, Mobil, or Pure One filter, for the filter may not be allowing pressure to build up (drain back valve issue).
 
#13 ·
Well, today i bought a napa gold oil filter, i changed the oil again for the sixth time, i test drove the vehicle after a 20 minute drive the oil pressure was holding around 35 psi at stop signs and red lights, until i stopped to get a soda, when i started it back up the oil pressure rose just enough for the check gages light to go off, i drove another 10 minutes on back roads starting and stopping pressure was low around 10 psi but no check gages light, so i stopped by a friends house for about 10 minutes, when i started it back up, no oil pressure the check gages light would not go off, so i started easing back home, at about 2000 rpm the check gages light would go off then come back on, the closer i got to home the more the check gages light would come on until about 2 miles from home it just stayed on.
Still there is no engine noises, no lifters tapping, just a smooth running engine, its like the more it runs the thinner the oil gets, the lower the oil pressure, its like the pressure relief spring gets hot and gets weak and loses tension, i checked tempature of the engine at the oil filter with a tempature gun temp is 175 degrees, it seems that if the problem were worn bearings the pressures would be consistanly low
 
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