johnfloyd82

ok ive been noticing when i start my engine up first thing it knocks before the oil pressure comes up, about two seconds after start up, then oil pressure comes up above 40 no knock, oil pressure remains normal at operating temp. this 4.0 has 192.xxx miles on it. would this issue be a worn oil pump losing its prime overnight? would the high volume oil pump be a good idea for my motor. does the oil go straight to the filter after the oil pump?

one more thing, since i did away with the mechanical fan ( got twin electrics) and replaced the roaring worn out ac pulley bearing i notice other noises.... when i idle it up to 2000+ rpm you can hear the rocker arms working, they all clatter( oil is comming up the push rods, oil pressure comes up with rpms) there is no lifters tapping theres no life threating knocks, the motor just sounds all around noisy. is this normal for these old inline sixes, my friend has a 2002 grand cherokee with over 200k on it. his 4.0 sounds quieter and smoother. just curious i wanna know that this motor is gonna be there for me, cant afford to rebuild it no time soon. appreciate any info.

kjc

Next oil change, try a quality oil filter.. wix or mopar for example. From what i've read and seen those filters (and others) have a spring loaded valve that prevents the oil in the filter from draining back out. Other filters, fram for instance don't have these check valves and the oil can drain out. Especially on many jeeps where the filter is at a funny angle.. sideways or even upside down. The short time it takes to refill the filter on cold start might be what you're seeing there.
And yes, many I6 4.0 have noisy lifters even with good oil pressure.

TurboPirate

You can try heavier oil depending on your area's temp, here in PR where the coldest temp is 87F in engines over the 100,000 miles I use 20W-50 and and oil treatment. If the noise goes away or if it gets less noisy with heavier oil then you can try changing the lifters.
TURBO

johnfloyd82

yeah i have thought about that upside down oil filter, sitting like that it would drain out, without check valve, i may try the mopar filter next oil change. i did and oil change with lucas and 10 40 on it last. it helped a little as the oil got miles on it the oil pressure delay came back

TheJerm

It really sounds like the oil filter check valve failed. 4.0L are noisy engines, mine sounds like a diesel

cruiser54

What brand of oil filter do you currently have?