why does my oil pressure go to zero?**UPDATE** - Off-Road Forums & Discussion Groups
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post #1 of (permalink) Old 04-14-2003, 07:15 AM Thread Starter
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why does my oil pressure go to zero?**UPDATE**

Prelim info: 1980 CJ7 with 4.0L just swapped.

I just swapped the 4.0L into the Jeep and have a couple of road outings on the engine and all was well. The longest trip was about 20-25 minutes long with a combination of country roads and a little city thrown in. The oil pressure was actually on the high side, about 60-80 psi. The engine has a lot of power and did not burn or leak oil. I decided to add some Sea Foam to the oil to try to clean the inside of the engine a little. I thought that it couldn't hurt. The next day, Saturday, I take it for it's first off road trip and that is when it started acting up. I drove 30 minutes to the trails and then 3 hours on the trails. Towards the end of the trails, I notice the pressure is down to 20psi. On the trip home, it actually dropped to zero. I immediately shut the engine off and coasted to the side of the road. I let it sit for a few minutes while I tried to call for some help, but couldn't find anyone home. So I fired it back up to see what would happen, and the pressure is back at 40psi. So I throw it into gear and take off. Within 5 minutes the pressure is back to zero. I repeat the process. Turn the engine off, immediately restart it and the pressure is back to 20psi. I drive 2 more miles and repeat. I did this a few more times and I finally get home.
I'm baffled about why the pressure goes to zero and then I turn the engine off and then immediately restart it and it's back up to 20-40 psi.
Could it be something as easy as a clogged screen on the oil pump or am I looking at a new oil pump?
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post #2 of (permalink) Old 04-14-2003, 07:21 AM
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Re: why does my oil pressure go to zero?

It could be as simple as a clogged pickup, or it could be clogged return holes in the head. Of course you cecked the level, right?

Pull the valve cover and have a look. Then pull the pan.
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post #3 of (permalink) Old 04-14-2003, 07:53 AM
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Re: why does my oil pressure go to zero?

1. It could be the oil pressure sensor being flakey.
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post #4 of (permalink) Old 04-14-2003, 08:24 AM Thread Starter
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Re: why does my oil pressure go to zero?

Yes I checked the level first thing. It was OK. The gauge is OK also I think because the engine started to rattle and clank right before I shut it down. It's a mechanical gauge.
If it is the screen, can it be cleaned out or do I have to replace it?
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post #5 of (permalink) Old 04-14-2003, 08:59 AM
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Re: why does my oil pressure go to zero?

I would reason that if it's the screen ...it can't be clogged all the time. If that was so ...you would still have poor oil pressure upon restarting. That is, if it is in fact debris clogging the screen ...it must fall off upon shut down and then re-accumulate after so many gallons of oil are drawn through it.

If I'm correct in this (I'm always open to opposing points of view).....changing the oil right after this event takes place should expel most of it out the drain plug hole ...unless you've got some really big flake of something in there. Repeat as needed.
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post #6 of (permalink) Old 04-14-2003, 09:16 AM Thread Starter
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Re: why does my oil pressure go to zero?

I'll change the oil and filter tonight and see what that does for me. That was my thinking also that the screen gets clogged up and then the particles fall back into the pan when I shut it down, only to be picked up again when I restart it. Maybe that Sea Foam broke up alot of gunk inside there and its laying in the pan.
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post #7 of (permalink) Old 04-14-2003, 09:41 AM
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Re: why does my oil pressure go to zero?

what weight oil are you running?

what was your engine temp during saturday's trail riding?

its my guess that the sea foam, coupled with the engine heat of trail riding, thinned your oil significantly to the point where the oil pump was cavitating and not maintaining normal pressure. that and the effectively thinner oil would be collecting in the top end, so when you shut it down it would drain back down and repeat the situation when restarted.

changing the oil should remedy this problem.
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post #8 of (permalink) Old 04-14-2003, 09:50 AM Thread Starter
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Re: why does my oil pressure go to zero?

oil is 10W40
Temp was right in the middle (stock gauge) halfway between C and H
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post #9 of (permalink) Old 04-14-2003, 12:55 PM
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Re: why does my oil pressure go to zero?

im with leve..
this has happened to me 3 times.. every time i freaked out...
every time it was the sensor.. i unpluggfed it, cleaned it out with alcohol, and reconnected it.... problem solved.
i'd look long and hard at it if the engine isnt making strange noises,. [img]images/graemlins/cool.gif[/img]
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post #10 of (permalink) Old 04-14-2003, 03:06 PM
 
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Re: why does my oil pressure go to zero?

I'd go with what GeeAea mentioned. This occurred to me on an older vehicle. There was lots of oil sludge built up, but pressure was fine. I thought I'd get cute and add one of those solvents to clean out the gunk. End result was that a quarter million leaks suddenly popped up and loose sludge clogged up all sorts of oil passages in the block. It was disposed of soon after.

Granted, this is "worst case," but still possible. Definitely check the sensor first.
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