Like a few other F150 owners I’ve spoken with, my 1997 F150 was plagued by an erratic oil pressure gauge. Specifically, when cold, the gauge would work normally. However, after the truck was completely warmed up (I commute about 25 miles each way to work), the gauge would begin dropping down, sometimes to the point of setting off the oil pressure light. Sometimes I could get the needle to begin reading normally again by fluctuating the engine RPM, but this “fix” was hit or miss. Although I was quite confident that the gauge was indeed malfunctioning, I could not completely ignore the fear that I really was dealing with an actual pressure drop.
A few days ago, I traced the wire leading from the oil pressure sensor (located very near the oil filter) to (behind) the dash. What I found was that the wire, encased in a high temperature insulator, was routed VERY close to the exhaust manifold (within an eighth of an inch). I theorized that, although not burnt, the wire’s electrical properties were being changed by the ambient high exhaust heat. I rerouted the wire completely away from the exhaust system (after encasing it in new loom/split casing), crossed my fingers, and went driving.

Problem solved!

A final thought – I do still believe it to be a VERY good idea to install a “real” oil pressure gauge as many on this board have recommended; I plan on installing a mechanical one in the next week or so. Anyhow, sorry for the long-winded post, but perhaps it’ll help someone, as reading many of you all’s questions/responses on this board has helped me.

Take care all,
Greg

 

my 2000 f150 does the exact oppisite. when it is cold the pressure gage bounces from normal to low and sets off the light. once it warms up it goes away. it is really driving me nuts and I hope that someone knows what the problem is and how to fix it.

 

I don't bother to install a "real" pressure gauge on my vehicles with dash gauges. I did spend the $40 on a oil pressure test gauge. On most engines it only takes the time of an oil change to do the test. It sure beats driving around wondering if you are destroying an engine.

Was this wiring problem caused by improperly routed wires? Does this possibly happen when someone pulls on the wire further down the line? Thanks for the tip, I'll look at the routing on mine the next time I do an oil change.

 

Could be...

Sending unit.
Clogged oil screen (In oil pan).
Oil pump.
Bad bearings.

NCHorseplay,

How many miles on your truck?

Does your oil look dirty?

What viscosity oil do you use? (5w30)?

Do you use Synthetic oil?

 

adaycj,

I can't answer in complete certainty whether the wire was misrouted - I bought the truck used, so it could have been molested by someone along the line. That said, I really don't think that the wire was moved. Before I relocated it, the wire was nicely nestled amongst other wires in what appeared to be an undisturbed factory loom. In fact, I had to remove it from this loom in order to reroute it. Additionally, the wire is encased in a high temperature wire protector/casing, suggesting that the wire was factory routed in close proximity to the exhaust.

regards,
greg

 

When cold, mine will fluctuate but will eventually read normal after warming up. Note: I just changed my oil and used 5W20. It had almost cured the problem completely except for one time right after the oil change. Its a lighter oil and maybe this points to a failing pump. I dont know.
Im thinking that maybe the fluctuating was caused by low oil level rather than a bad pump or sending unit or wire ............

 

Lighter oils are recommended for cold temperatures. The pump is going to have a hard time pumping thick oil. If the gauge goes normal when it is warmed up then maybe the oil warmed up and can flow good.

 

Well it is pretty Damn cold here in Boynton Beach Florida, gets down to like 55 at night.

 

Then oil was not your problem unless you were running 75w90 gear oil in your engine LOL. sounds like something slightly gummed up.

 

temp1

my truck has just under 60k.

oil looks good, it still does it right after an oil change

yeah i use 5w30

i use synthetic or synthetic blend

 

NCHorseplay,

I can only guess about the sender, oil screen, bearings or oil pump so good luck if you dink around with it and also if you end up taking it in for service.

Larry

 

The only thing not mentioned so far is what seems (no proof, but nothing else fit the symptoms) to have killed my 5.4; the oil pump bypass valve.

If it is sticking, you will get indication of falling and/or loss of oil pressure. Which is what is happening, because when the valve opens, it dumps the pump output to the pan.

And, just for academics, when you lose oil pressure the first thing to go is the right side camshaft bearings.

This occurred in my truck after the Dealership re-did the leaky right side head gasket. The assumption was that during that repair something fell into the oil galleries and fouled the valve.

Hope this helps.