I've got a 91 F-150. Over the last few times I've driven it, I've noticed that the oil pressure gauge reads lower and lower. At first I began to think bad oil pump but the engine runs fine and has not had any issues which leads me to believe it is possibly a bad gauge. Had anyone else experienced this issue?

 

Hate it when the oil pressure shows low! Pucker-time starts, but might be nothing.
But it might be low oil pressure too!

How low does it go? Do the fuel and temp gauges read a bit lower as well do you think? Or do they look normal?
Did you do anything recently, such as change the oil?
Just throwing out thoughts as they pop into my head. Never had a gauge go bad on any of my Fords (just jinxed myself probably) so don't have any personal experience.

But you can test it. First by removing the wire from the sender and grounding the tip to see which way the gauge needle swings.
Someone else will have to tell you what it should read. With the old gauges, grounding the wire would have slowly (the gauges were heavily dampened) rise to above full. I know they changed the values/ohm-range of these things though, so don't know what yours would read.
But at least it would tell you that the gauge is doing something correctly or not.
You can test the sending unit as well, but I'll have to read up on what the readings should be.

Did you happen to change oil recently? If so, what filter did you use? Again, I've never experienced a bad one, but people talk about them all the time.

Good luck. Sorry I didn't have any direct answers for you. Just commiserating while waiting for some genius to say, hey, reconnect that wire under the hood!

Paul

 

you 91 has an oil pressure "idiot light" gauge. it is not a real gauge. it will either show pressure or not. as long as it has over around 8 or 9 psi oil pressure the gauge will show oil pressure.. if the oil pressure drops below the switch setting it will read zero.

 

It started around almost the middle, now it is just past the "L". Fuel gauge reads accurate but temperature does not. The temperature gauge is my Tempo does not work either which is another factor that led me to possible bad gauge. Oil was changed over the winter, late January/early February. I took the truck down to Florida over the winter and the gauge read close to the middle.

 

Based off what you're saying, everything should be fine?

 

I'd never heard that. But if it's true it's a good thing to know!
That's just the type of statement that's ripe with potential for sarcasm of course, but I don't think he was being that way. And it looks like Tom/tjc would be in the know. What with "almost too many Fords" to his name!
Now, in that statement, I do sense some sarcasm brewing!

I just wonder at Ford or any OE doing such a thing on purpose, when an actual gauge is simple, would give the operator much more information, and is inexpensive to produce. Just "not as inexpensive" I guess would be the answer to that question. After all, dollar saved here, times tens-of-millions of vehicles will definitely add up.

So I guess you'll never see pressure rise to too much, or lower to too little, until the gauge goes to zero. Shame...
But does that lower reading mean that something is wrong with the instrument face itself then? Like more resistance lowering the needle's reading? Maybe whatever is going on with your water temp is related to what's now going on with the oil pressure.

Hope it's a simple issue to deal with. If nothing else, it's annoying as hell to have gauges read different from what you're used to as "normal" running!

Paul

 

I had the same issue with my Oil Pressure Gage, changed the sending unit and it came back into the "Normal". Sending units are cheap so I recommend changing it before opening the Gage cluster

 

yup, as long as the gauge is not sitting all the way left and not moving at all, it is fine.

i agree it that can be seen as sarcasm, but i ain't that casual with sarcastic hints!
when i get sarcastic, you damn well know it!!
we see this question every now and then in the IDI diesel forum with people freaking out about "low oil pressure" when they put a real gauge and sending unit on their engine and then freak out because it "is low" but the stock gauge says it is "normal". anything over 7-8 psi at idle on a hot engine is perfectly fine.
ya got to remember, once you increase the RPM's ,the oil pressure goes up too.

agreed. a sending unit is cheap enough at around $15.
the old one may be failing and changing the Resistance of the sender causing the gauge to read differently.

 

If this makes things easier, this is my current reading at idle. It stays there when driving as well.

 

Do you by any chance know the location of it?

 

I believe it is located on the driver's side of the block, just above the oil filter.

Edit: The sending unit has pipe threads, (I believe it is 1/8 NPT male threads) I installed mine with Teflon thread tape, wrap the tape tightly in a clockwise direction looking at the threaded end, start the tape at least 2 threads from the end. That way there is no chance of Teflon fibers getting into the lube system. Good Luck!

 

Well known and well documented. Follow Subford's links in this thread.

https://www.ford-trucks.com/forums/1...ure-gauge.html

Tom? Sarcastic? Nah!

Correct and to add a little accuracy, front of the block, just behind where the mechanical fuel pump used to live.

Ford actually went to a great deal of trouble and expense to make the fake oil gauges and they were commonplace in the era. It was a response to unsubstantiated warranty claims when the idle oil pressure dropped after break in on a new vehicle. Really not a problem, but somewhat characteristic of the Ford design.

The gauge clusters were actually modified with a cut to the printed wiring and a resistor added to make the gauge read center scale when the sender closed. You can test yours by grounding the sender wire at the engine. If the gauge reads center, your sender has developed some internal resistance. If your reading remains low, the gauge itself may be faulty. If it reads high, I would suspect somebody has already attempted to make a real gauge out of the factory cluster and has bypassed the resistor.

The gauge type oil senders look like a bell and are noticeably larger than the switch type senders which look like a small plastic bump on top of a hex nut.