Steep climb oil pressure drop?

While wheeling a couple of weeks ago, I had a few long, steep inclines that I had to make high RPM runs at. When at the steepest part of the climb, my check gauges light came on and the oil pressure dropped to zero. I backed out each time and the pressure would return to normal. Fresh oil change and good level. Crawled through some trenches where it was just about laying on it's doors with no issues so it is definitely a nose-up issue. Guessing the oil is just running away from the pickup? Pulling the pan to check pickup and screen. Not ready to drop $400 on Morosso deep sump pan. Almost as much as I paid for Jeep.


98 XJ 4.0

I would say that there is something wrong with your p/u. I've been up/down on the steepest trails and never had a issue.

Are you sure the oil return galleys are not clogged with sludge ? A below Zero winter cold start likely causes more wear than a moment of two of low oil pressure on a steep climb. If you didn't pay much for the Jeep, just run thicker oil and call it fixed.

Run&Gun said:

While wheeling a couple of weeks ago, I had a few long, steep inclines that I had to make high RPM runs at. When at the steepest part of the climb, my check gauges light came on and the oil pressure dropped to zero. I backed out each time and the pressure would return to normal. Fresh oil change and good level. Crawled through some trenches where it was just about laying on it's doors with no issues so it is definitely a nose-up issue. Guessing the oil is just running away from the pickup? Pulling the pan to check pickup and screen. Not ready to drop $400 on Morosso deep sump pan. Almost as much as I paid for Jeep.


98 XJ 4.0

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The oil pickup is in the rear of the pan, so if you are climbing uphill, the oil would run TO it, not away from it.

One reason I am not a fan of high volume oil pumps...over time, the drain passages get clogged, and the pump can do as yours seems to be doing,....pump oil up top to the head faster than it can drain back down to the sump.

Running a thicker oil would make it worse if it is a drain issue.

Now, if your oil pump pickup has gotten loose at the pump, it could start sucking air on a climb, which would give you the same issue.


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TRCM said:

The oil pickup is in the rear of the pan, so if you are climbing uphill, the oil would run TO it, not away from it.
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Most definitely; more oil there on a climb on a 4.0L.
No reason for a deeper pan - just more stuff for the front axle to hit on the way up.

The OP didn't say he has a HP pump, or what his base oil pressure is.

OBDII XJs like to play a game where the gauge at fault will drop to zero.
Since it sounds like $400 is just about what he paid for the Jeep may imply high mileage. In which case, the oil pump may be working to the best of it's ability, and the mains are worn to the point where at normal load the oil pressure is enough to keep the PCM happy, but under extreme load, the oil pressure drops below what the factory has deemed normal and the PCM kills the gauge and turns on the CEL.

Either way, a fancy new oil pan won't fix it. Sounds like it's either time to pull the pan and look around, or drive it like you stole it and accept it that the engine may not have a super long service life in it's future.

I would pull the valve cover, make sure there is no excessive sludge, and then drive it like it was stolen. Lots of Jeeps have driven lots of miles with low oil pressure.

WB9YZU said:

The OP didn't say he has a HP pump, or what his base oil pressure is.

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Neither did I...............I was just stating one issue with a high VOLUME oil pump, especially when someone replaces ONLY the oil pump in an other wise high mileage engine. Suddenly the pump can move oil faster than it can drain back to the pan.

Then later on, they wonder why they have oiling problems.....like he seems to be.

No high pressure pump. Original stock engine, 200k on the clock. Gauge reads 40 when cold, 25 after a long day. I'll pull the pan and start there.

I've been offered another 4.0 with a spun bearing for free. Probably should take it and start a rebuild so I have a spare when/if this one tanks.

Cold pressure reading has no significance. 35-50 psi at 55 mph and 10-20 psi at warm idle is what you should be seeing, assuming the Oil Pressure Sensor is functioning correctly.

might try replacing the oil pressure sensor 1st....may be cheaper...or hook up a mech gauge to see what you are really getting for pressure on those climbs