96 Explorer 4.0 - Low/No Oil Pressure

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FusilliJerry82

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Jun 3, 2006
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Location
Philadelphia, PA
1996 Explorer XLT 4.0 OHV, 186k

The oil pressure gauge plummeted to nothing one day despite no noises or sharp increases in temp. So I keep driving it and the gauge keeps fluctuating between normal and nothing (mind you the gauges in these trucks are dummy gauges, they read normal at any pressure except under a certain threshold at which they read 0). A bit and later, I start to hear a bit of light rattling conducive to low oil pressure, but not no oil pressure. I pulled over and sat for a while and tried it again, and pressure was fine, and the rattling gradually went away. Then it happened again and I kept stopping and going until I got home. I changed the oil out from some Quaker State synthetic with about 2k on it with 4 quarts of Quaker State 10w40 conventional and a quart of MMO. First, after a test drive, all was well and then it plummeted again. So I've been driving it because I have no choice and its odd. It will go for tens of miles without issue and then randomly do it again for a time, and randomly come and go. It seems the longer I let it sit, the less likely it is to do it for a while.

This has happened before but was "cured" with a simple oil change, which I presumed was a clogged filter. That was a few years ago.

So what are you're thoughts? I honestly can't justify doing anything involving removing the engine (which includes dropping the oil pan in this truck), considering it would probably cost more than the truck is worth.
 
More than likely it is a bad pressure sensor. Or a connection or wiring. Possibly the gauge itself.
An oil change can clean or change things at the sensor - this may be why it 'fixed ' itself for a while.
 
I think my first step would be to buy a manual gauge for 10 dollars and hook it up instead of the dummy light, so you know for sure what is going on in your engine.
 
Originally Posted By: FusilliJerry82
This has happened before but was "cured" with a simple oil change, which I presumed was a clogged filter.
The oil filter has a bypass valve that would open if the filter was clogged.
 
I replaced the sending unit a few years ago after it read zero at all times and it worked again. I don't think the sending unit is bad because I'm actually hearing some rattling in extended periods of low pressure.

I'm considering doing a seafoam in the crankcase and checking whether my thermostat is stuck open (it rarely goes above 1/4-1/3 up the gauge) causing any sludging.
 
Originally Posted By: FusilliJerry82
I already did with the oil.


Then it may be just the sender. Only way to know for SURE is with a REAL gauge.
 
I would do as mentioned and use a pressure guage to check oil pressure. If you have good pressure, then consider fixing the oil gauge of course. If you still have low pressure and/or noise, perhaps you have sludge blockage, which the MMO should help address. I would change out that thermostat. If it doesn't clear up then the engine probably needs disassembly and inspection.
 
So a couple months back, I tried using one, then two cans of Amsoil engine flush at a fast idle for like 30 mins and no difference. Changed the oil then tried overfilling it to see if it helped at all. 2+ quarts over really quieted it except the top-end continues to chatter. Other than that it still runs well though.

Seeing as this truck has basically now been written off and replaced in its role as a daily driver, I think I'm going to make a last ditch effort of filling the engine up (to the brim of the filler) with either kerosene, diesel or paint thinner, leaving it to sit for several days, cranking it for a few seconds, then draining and filling with 20w-50. If this doesn't work, oh well, but it would be nice to bring it back from the dead.

Any thoughts? What I should use to soak it?
 
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Also, this was all after, not too long after my post before the last, I had driven it in a snow storm one night (only 4x4 in the family) with the fluttering gauge, and have not once since then gotten any reading on the gauge. Got noisier too. That's when the Amsoil flush came in.
 
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The pan can't be removed without removing the engine, which requires money, experience and time I don't have.

I have a feeling its sludge because I don't think the engine would have lasted this long being beaten this much with truly 0 pressure.
 
I don't remember how the filter is mounted on the 4.0L (I haven't changed the oil on one in at least 8 months, lol) but what you COULD do is:

1. Remove the drain pan bolt.
2. Remove the oil filter.
3. Hook up a small hose or tube through the FEED inlet(s) on the oil filter housing (NOT the centre tube, which is the OUTLET; it feeds the engine filtered oil) and GENTLY pour something like mineral spirits or kerosene into this hose from a slightly elevated location.

This will back-feed the pump, and should flush the screen. You will be able to observe what it removes by what comes out the drain pan plug hole. Once it is dripping clean, maybe put the plug in and let the pan fill up a little and sit for a bit. Then drain again.

This would avoid putting the solvent/cleaner through parts of the engine where it could potentially cause damage, like the valvetrain.

As a final step, I would recommend dumping some oil down the tube when you are done your flush to preventing anything from "dry" starting.
 
Originally Posted By: FusilliJerry82
It's vertically mounted so I don't know how well that would work.


Yeah, without some sort of adaptor, it will make it difficult. You could always cut a hole in a filter and thread a fitting into it and feed it that way I suppose? That's a bit of work though.
 
Something that's a good solvent I imagine, LOL. Might try just doing a few inches of the oil pan first.... Could clean off the screen without getting solvent through the engine.
 
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