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Pathy87

Low to no Oil Pressure

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Hi there, I have an 87 3.0 pathy with 212,000 miles on her. When I start it up, oil pressure is great, as the engine heats up, it drops lower and lower. Once at running temp, the oil pressure is at 0 and the oil light comes on. 5 days ago I changed the oil and filter, as well as a new sending unit put in (old one shorted out and was maxing out the oil pressure gauge).

 

When its low, I don't hear knocking or anything, performance wise nothing changes. My pathy is running very rich right now, but not so rich that it thinned out the oil that quick.

 

Rock auto has a cheap sending unit, and an expensive one, I tried the expensive one first, that did the same thing until a bare wire touched metal then shorted out the sending unit.

 

This time I bought the cheap sending unit.

 

Should I run thicker oil? Anything else I should look for? During my next oil change, should I have the filter and oil inspected for excess metal? I figure this old dog is just tired and about to die.

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Verify the actual oil pressure. Harbor freight has an oil pressure test kit for pretty cheap. Make sure there is actually a problem before you spend more time and money chasing this.

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+1 for double checking, but if both the oil pressure gauge and the idiot light (I'm assuming the sensors are separate) indicate a problem, I'm inclined to believe them.

 

Was it doing this before you changed the oil and filter? And did it continue doing this immediately after, or do alright for a while and then develop the issue all over again?

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I would double check the pressure. If it really had no oil pressure the top end would be ticking like crazy. Could be a worn oil pump, worn bearings, or just a ****** sending unit. I believe it is the same unit for the gauge and the light.

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https://m.harborfreight.com/engine-oil-pressure-test-kit-62621.html

 

There you go. We had our 150kw mobile generator at work that was showing low oil pressure. I told the guy working on it to verify the problem and bought this kit to check it. Went cheap because it will probably be the only time we use it. As suspected, the actual pressure was fine, but one of the wires on the back of the gauge was loose, tightened it and everything was back to normal. Point being verify the problem, and the kit is good quality for the price.

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Thank you all for your suggestions! I will purchase that kit and see what I find. I sure hope its just a faulty sending unit or loose wire.

 

To AdamZan : When I first start the truck in the morning it has ticking for the first 3 solid seconds or so until the oil gets slung up to where it needs to be, after that its fine.

 

To answer SLARTIBARTFAST :

 

When I bought the rig the sending unit didn't work at all. The pressure displayed 0 but no oil light was illuminated. (odd)

 

I then purchased a $40 sending unit, put that in, showed 60psi until it reached operating temperature then it would drop to 0 and idle and about 10-15psi while driving. A wire came out of the sending unit plug and touched the frame, which then made the sending unit display 120psi. (again, no oil light illuminated). I drove it like that for a year or so.

 

I finally bought another sending unit, eliminated the sending unit plug (made my own connection and soldered it) The oil pressure reads 60psi until it warms up and then drops to 0 at idle (oil light illuminates now when at 0), and shows maybe 15psi while driving after it has reached operating temperature.

 

I'll buy that testing kit and update you guys with the results!

 

Thanks again!

 

 

 

 

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Thank you all for your suggestions! I will purchase that kit and see what I find. I sure hope its just a faulty sending unit or loose wire.

 

To AdamZan : When I first start the truck in the morning it has ticking for the first 3 solid seconds or so until the oil gets slung up to where it needs to be, after that its fine.

 

 

Yeah, that is kind of normal as they age if the oil hasn't been changed religiously. Not a big deal. Mine does it every now and then.

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+1 on the startup ticking being fairly normal on these. Also makes sense that it should be ticking like crazy if it truly has no pressure at idle--and it certainly wouldn't have survived a year of driving with no pressure. Hopefully the pressure test clears things up and it's just bad wiring or a bad gauge rather than the bearings or pump being on their way out.

 

For reference, the 89 manual suggests at least 9 psi at idle and 67 psi at 3200 rpm with the engine warm. (The 94/95 manual lowered the 3200 rpm spec from 67 to 65, for some reason.)

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Update: I know this is old, but the oil pressure switch works fine. At low idle, it doesn't like to register much, but once up and going, the gauge reads good.

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Joy of joys - may latest winter camping trip to CO this past Dec, my idiot light started dimly turning on.  So dim I wouldn't have noticed but for it being at night.  Then got brighter, dimmer, off.  Dim, bright, off.  Pulled over to check oil level - had just done an oil/filter change week before the trip.  Level good.  Was in the middle of BF nowhere between Wichita Falls and Decatur, middle of night on a work night, so no help on the way lol.  But as someone mentioned, there was *no* racket from the valve train.  I've run it a bit before on low oil, low enough for the sump to slurp air and yes, it will begin cyclically tapping up top if pressure drops too low.  So I strongly suspect a bad sending unit, or the wiring (the wire has yanked out of the spade connector multiple times, so I know it's a potential point of failure, could be grounding).  The behavior mine exhibited - on throttle up, light would brighten.  Chop throttle at highway speeds light would go off.  Also, light would flicker in sync with road bumps and whoops.  So hopefully my intuition is correct.  Have a set of Auto Gauge gauges to install to day for a second opinion.  The light issue is still intermittent after getting it home, but as you can imagine it's been parked almost the whole time since getting her home, minus taking it to get inspected.

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Check the wire and sensor. My original was cut up and sensor was faulty from all the oil and grit covering it up over the years.

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Dim light/fluctuating with bumps sounds like a wire or sender issue to me too.

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Seems 30-ish years is the lifespan of 2-door Pathfinder oil pressure senders.  Not too bad.

 

Unfortunately OEM replacements are impossible to find, and the aftermarket replacement options are inconsistent at best.

 

When I bought my truck the pressure gauge would show zero at idle and barely register at cold start and when warm revving.  Light never came on.

 

The first replacement sender I got worked better, sort of, shooting up to 60 on cold starts but still zero at warm idle.  At one point the oil light came on and stayed on, even tho the gauge still would show good pressure when driving.  So after a mini heart attack, time for another sender and mechanical pressure test while I'm at it.

 

Mechanical test showed excellent pressure from cold to hot.  The new sender I put in now makes the gauge max out at 45 on cold starts, 15 at warm idle, and around 20-30 driving around.  Still bugs me that it doesn't show true OP.  Sometimes I play around with the idea of removing the sender and routing a mechanical pressure gauge to the dash.

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