For anyone who hasen't read my earlier posts on this truck, it is a '78 F-250 4X4 351M Automatic.

I got the Oil Pan on the truck, still leaking some, so I'm still in the market for a new one. Anyhow, I took the truck home tonight and noticed the oil pressure fluctuates with the engine RPMs. Is this normal? When at idle, it registures little to no pressure, but at highway speed, it registures almost middle of the pressure gauge, just a shade on the low side.

I think this might be normal, but I don't know. My only real experience on this is with my Dad's '90 F-150. I know it's pressure does not fluctuate, but I think it also has an electric oil pump, so I wouldn't expect it to.

Thanks,
Cory

 

It's normal for the oil pressure to fluctuate, however some gauges move faster than others so it is more obvious on some vehicles. Factory gauges are notoriously inaccurate, if your concerned about oil pressure install an aftermarket gauge. If you think the pressure is too low, try running a thicker oil.

 

The 351M/400 had oil pressure problems.These are even more noticable when the engine's have many miles on them.

You can read all about them in the 335 engine series forum as this is a engine related question.

 

Stock gauges are also nothing more than "idiot lights with pictures" as a friend of mine refers to them..... (you know who you are if you read this )

Check the sending unit perhaps........