I have A 1993 Ford F-150 with the 300 Straight Six with 250,738 miles, I understand the factory oil gauge is just an "idiot light" but after I've been driving for a while and the truck is warm if I come to a stop light or stop sign the gauge goes crazy. It bounces between L and H very rapidly, or it will just drop to L then the engine will rattle but pop right back up if i increase RPM's. I've replaced the little sending unit on the side of the engine next to the oil filter, but that didnt fix it. I never noticed it until after I had blown the timing gear and had to have it replaced. I'm pretty good about changing the oil regularly. I use Valvoline MaxLife High Mileage 10W-30 Synthetic Blend, right now it has a Fram oil filter on it but will be getting a different one as I see that most say they are junk ( Last time I listen to a Chevy owner ) I'm also going to pick up a mechanical oil pressure gauge just to see what the actual reading is.

Any input would be greatly appreciated.

 

Yeah, pull that crappy Fram filter off and buy a Motorcraft. See if that helps any.

 

Pull out your oil sending unit, clean, crank the engine, see if oil comes out the hole.
Now, if I pulled out that sender, I'd have a new Motorcraft one going back in.....

 

Update 1/27/19

I've installed a new oil filter, removed and cleaned the sending unit, then hooked up a mechanical gauge. I used a brass tee so I could use both. The factory gauge still goes crazy and the mechanical one sits between about 8 psi while the other one goes crazy at a stop. In reverse on the other hand, the factory gauge goes to nothing and the mechanical gauge sits about 2psi.

 

Is that add-on gauge electric or does it have an actual oil tube? The one with the tube is mechanical. I've seen many aftermarket electric gauges read a bit low. I'm wondering if the sending unit for the factory gauge is needing replacement.

 

If you really have 2 psi, then the factory gauge won't register. When you have 8psi, it may behave erratic as really it only registers at 7psi, so that may be part of the problem. That only occurs you say when it's warm.

What is cold psi?

It sounds like the mains are really worn. Does it have some low end clunking when starting cold?

Perhaps the oil pump is scored from the nylon timing gear that exploded.

 

The add on has the oil tube running to it, the sending unit is about 3 weeks old.

This morning it was about 45psi at 3°F outside I haven't heard any kind of clunking when starting it sounds great at start up. Just rattles when warm and the gauge is going nuts. I also let the truck sit in reverse while cold and the pressure just continued to drop from 45psi I stopped at 25psi but I'm sure it would have went all the way to 0. It jumped right back to 40-45 when I put it in park.