I recently picked up a nice 97 F-150 XLT Mark III from a co-worker w/ 90k miles. It's pretty clean for it's age. I put it into storage for the winter while I was away. After picking it up in February, the oil pressure has been acting funny.

I've put on several hundred miles, maybe a thousand, since Feb/March with these symptoms. I can't figure out of it's an electrical or mechanical issue. Oil was changed with 5w30 2 weeks ago (6 qts).

-In the morning, the gauge is at around 70%, which is where it normally and has been before normally (for the previous owner also).

-After a bit of driving, the pressure will drop to 25% and, while driving, slowly work it's way back up to 50% - 70%.

-Sometimes it will drop to 0% and the light will go on. If it turn it off and on, it will reset the pressure and I continue on. Usually it will work itself to the 50% - 70% range.

-Braking, slowing down, or putting it into N with some gas will get the pressure back to 70% momentarily.

-This morning, as I got on the highway, it dropped to 0% with the light coming on. I pulled over, restarted, and continued on. It did it again but slowly creeped up to 50% after a few minutes.


So my plan is to get a new pressure switch, possibly a mechanical gauge, and to hopefully borrow a ODB module someone has that hooks up to a laptop to do some real time readings. Is there anything else I can look into?

Thanks.

 

It sounds electrical.... I believe your gauge is binary either 0 or 1. Unless the Mark 3 actually has a real gauge. A real one will bounce around from 20 to 90 psi as you drive around in the mornings to fully warmed up. If you gauge stays at a constant pressure when cold and warm without dropping its definitely a dumb gauge.If you are getting readings halfway, its not pressure related. Sounds like the sensor is going.

I installed a mechanical oil pressure gauge last year and the factory gauge doesnt "track" the dummy at all. But I have a basic F150...

 

Thanks. That's a bit reassuring. I guess a new sending unit is the next step.

Concerning the oil pump, are these known to go bad or anything?

 

Quick update:

In the afternoon (warm day), the pressure was all over the place. 0....20....50....70. Eventually it leveled out at 50 on the highway. On the way home at night (cool, rain), it was constantly pegged at 70 the whole way.

So are these symptoms of possibly a bad switch/connection? Or should I be worried about the pump going?

Thanks.

 

What is the pressure when the truck is cold and you accelerate from a light? Oil pressure should be maxed. Cold or high RPMs = high oil pressure. Hot engine at idle = lowest possible oil pressure.

I would replace the sending unit as quickly as possible.

 

The factory gauge will never really move because once the engine builds like 8psi it goes to about the middle of the gauge. Try to change the sender.

 

For the past 2 days, I did ~200 highway miles and the gauge didn't move an inch (or even 1/8") for the high end. That's why I was worried when it would bounce around from 0 to 30 in the mornings.

Here are some pics of what I've seen lately. It will either drop to 0 or this level and slowly recover, usually within 5 - 10 of starting:



After it recovers, it hovers at:


On a normal day, it won't move at all after starting (cold, hot, etc):

 

The oil pressure guage is nothing more than a glorified idiot light. If the oil pressure is 8 psi or higher, it will indicate as shown in your third picture. When the pressure gets lower than 8 psi then it will start falling. If your oil level is good and the truck is running good, then the sensor is bad. Replace it. Good luck!

 

It sounds like you guys are all having problems with the oil pressure sender which doesn't surprise me at all. They are relatively cheap but can be a pain in the butt to replace.

 

Yup, and normally I wouldn't care. I just get nervous when I'm on the highway and pressure drops to 0.