My '94 150 V8 oil pressure guage has started fluctuating. Normal is half scale, but it will randomly move to quarter scale, then back up to half, any operating temperature. I'm confused if the sender is a switch or if this could be the guage itself. I'm sure the pressure is ok. How easy is the guage to replace if that's the problem?

 

If it didn't fluctuate before(ever), it has the stock oil pressure sender, which is not really a sender but rather an on/off switch. The gauge either shows normal, or it drops all the way to low if it dips under (I think) 6psi. If it's fluctuating there's probably a rotty wire somewhere, or I suppose the sender could be dying. I wouldn't worry too much about it.

It's fairly easy to convert the stock "idiot light gauge" to a real gauge and a lot of people have done it, in which case the gauge should fluctuate during driving. You just swap the stock sender for a real one, and bypass a resistor on the gauge, and it works for real.

 

Ugh....I had a Toyota 4x4 where the oil pressure gauge dropped and bobbed.

I knew nothing about cars then...and within a couple hundred miles the engine seized. The oil pump was going out (I later learned)...and that took out the engine.

Probably just the gauge/sender...but just keep an eye on your oil levels.

Also, loose grounds can cause weird things like that.

 

Normal in these trucks is not half way on the gauge. It should read almost to the "L" in normal.

I would start by replacing the sending unit, and go from there.

 

How are you sure?

Unless you've hooked up another unit and monitored pressure, you have no idea. There could be a problem with your pump. There could be crud intermittantly blocking your pickup screen. You need to beg, borrow or steal a mechanical gauge, install a T at the sender, hook up both gauges in parallel and monitor your real oil pressure when the electrical gauge drops. That will tell you if there's a real problem or merely an electrical one.

 

Anybody know of a diy write-up for this? TIA!

 

You don't really need a write up. Just go to napa or someplace, and get an oil pressure sender for whatever motor you have (302 or 351). Put that in place of the stock "on/off" sender.

Then take the gauge cluster out, there's a couple screws hidden behind trim panels that just pop off and a tab on the headlight **** to remove it. You'll see one resistor on the back side of the oil pressure gauge. Just get a short section of wire, and jump the resistor with it. The gauge now works, though there's no actual PSI markings. I'd just as soon install another gauge and screw it to the dashboard or something, you can get an oil pressure gauge/line/fitting kit at most auto stores for like $20.

 

Make sure its the sending unit because my parents suburban the gauge was reading low for a couple of week then started it one morning and was knocking like a son of a b&^ch. Luckily it was the top of the motor we replaced the oil pump and it was like new.

 

Thanks!

 

I am looking right now for the write up on adding an mechanical gauge while keeping the stock gauge functional. Ill post it when I find it.