Reader Question: Fluctuating Oil Pressure Gauge

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Here’s the latest reader question, along with my reply! 

John asks: I have a 2000 Ford Ranger, 4.0L. The oil pressure gauge, when off throttle, rapidly falls to low pressure then to normal. It returns to regular operation when I open the throttle (or increase the RPM). Could this be a faulty gauge or sending unit?

My reply: Most modern cars have electronic gauges – i.e., they receive a signal (from the sending unit) and this is translated into a reading on the gauge.

It is more likely than not that an erratic reading is the result of a sending unit problem or the gauge itself rather than a mechanical problem with the engine/oiling system.

However, oiling problems can be very serious problems and should never be taken lightly.

I would avoid even running the engine until I knew the oil pressure was ok.

First, check the oil level. Sounds simple – and it is. But people sometimes forget and the engine gradually runs low due to routine consumption and that can easily trigger a noticeable change in the way the gauge reads – as well as bigger problems to come, if you don’t top it off!

Next, check the sender – and wiring – and the gauge itself. I’d start with the sender because it’s easier and more likely to be the source of your problems.

But, whatever you do first, avoid running the engine until you figure out why the gauge is reading erratically!

. . .

Got a question about cars – or anything else? Click on the “ask Eric” link and send ’em in!

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  1. In the mid-late 1990s Ford switched to a oil pressure ‘gauge’ that was binary. It reads either normal or nothing. Now maybe the ranger retained a real gauge longer? I don’t know. Anyhow the logic apparently was that too many idiots were bringing their cars in under warranty for the normal changes in oil pressure. Ford decided to ‘solve’ the problem by making it the gauge binary.

  2. This probably is the sending unit or connection or gauge problem. He doesn’t mention if it happened suddenly or got worse over a fair amount of time.

    Yes,I’d definitely plug a manual gauge into it and be sure. The way it goes up and down with the throttle is indicative of worn main bearings……if the gauge is correct.

    My 2000 Z 71s oil gauge does a fast fibrillation that bugs me but it stays in the proper range. Every gauge on it except the coolant…..thankfully. To say it has trouble codes is an understatement. ABS is always on and should be since it doesn’t work, just as I prefer. In the ‘information center”, or as I call it, the “disinformation” center or maybe more accurately, the “propaganda center” constantly goes from one error message to another. Check oil level constantly even though it’s always full of Amsoil Premium 5-w30. Check 4wd, check coolant level even though it’s full and has a new water pump, low fuel warning even though you just topped it off. I know there’s a problem with the sending units on several years of these POS so no sweat
    This truck and others friends have has changed the way I think of GM light trucks. Recently a friend had the crank break on his Duramax with 154,000 miles. That’s inexcusable even if it has led a hard life which it hasn’t even though it has a work bed and sometimes pulls a tandem dual gooseneck with some heavy loads.

    I’m desperately looking for a 90 to 95 GM pickup, preferably the 6.5 Turbo Diesel which I suspect a Dodge 7 speed manual would fit. GM nearly cornered the market in the 90s so they’re making up for it with cheap cheap cheap.

    At one time CEOs knew some specifics about the company. Those days are long gone.

      • Eric, my oil gauge does that fibrillation but I can’t imagine the pressure changing 2 to 3 lbs a few times a second. I have seen engines with badly worn bearings fluctuate quite a bit. When you back off the throttle and the pressure makes a quick rise and then falls off it can be indicative of worn bearings and if mine did that I’d check it with a manual gauge.

        Honestly, I don’t recall having a vehicle I didn’t put a T where the oil sensor is and hook the idiot light or electric gauge and add a manual gauge. GM had that same weirdly shaped idiot light sensor for the idiot light for oil pressure for decades.
        No doubt my special socket that fits it will survive me…unless someone just chunks it not knowing what it is. I’ll be beyond caring.

    • My silverado’s oil gauge fluctuates a bit under and off throttle but it is normal. My Xterra does not and it stays in one spot (a previous eric article asked if it was truly measuring anything at all if gauges do this?)

      • If you have an LS engine the oil pump is “variable”, one of the reasons I’ll be surprised if any will survive half a million miles like the old flat tappet TBI 350.


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