Oil pressure in a 4.0

BigClay

BigClay

Knower of useless ZJ things
Joined
Sep 24, 2008
Location
Winston-Salem
What is the ideal oil pressure in a 4.0 (mine is a 98)? The motor has right at 200k miles, so I am sure tolerances are loose, but the oil pressure is running about 20 to 40, but usually closer to 20. There are no knocks or pings (not even any lifter tick!). Should I run thicker oil to increase the pressure? Thoughts and opinions?
 
Same here, Mine runs around 50 at idle when cold and maybe 10 when hot. About 2months ago, it was dropping to zero, out a sending unit on it and it doesn't get below 10 now. Motor is a little noisy when cold buy quiets down when warmed up. 140K on her and I will stroke it when she goes, if it ever does. Inline power!!
 
the smartest thing to do is put a mechanical gauge on it and check it.
my zj runs between 40-60 and if it drops below 40 i know it's time for an oil change.(just passed 250,000 miles)
try a heavier oil, and don't be afraid to try a straight weight oil (sae 30).
i also add half a bottle (one quart) of lucas to my oil changes on anything with over 100,000 miles.
if i had to estimate, 75% of the time the oil pump is not the cause of low oil pressure.
 
15w40 Rotella T, 10-15k interval, 40-45 cold idle, 50-55 cold driving, 30-35 hot idle, 40 down road hot.. ~302-212+155 = ~245k mi on the motor.

has a rod/piston slapping/knocking, spark missing, hard hot restart (surprised my starter and battery are holding on lol.. 30s spinning over before hot restart) it does hit 15psi while cranking and not starting.
 
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