i have just became a proud owner of an 85 f-250 4x4 diesel. my question is about the fuel water separator for the diesel. can i just unscrew the filter, like an average oil filter for example? but i also heard that the new filter needs to be primed first. but a cilton repair book says different. i really am in need of advice.

 

Many previous owners of this model removed the original fuel filter and fuel-water separator due to problems & used something like a Racor combined filter & fuel water separator.
I don't know what 'priming' amounts to. I replaced my fuel filter twice while it was OEM. I filled the new filter with clean fuel before installing it, and cranked the motor twice before it caught. It burped a few times to clear the air in the lines & then ran fine.

 

That's what they mean by priming it. Also, before you do any of this warm the engine up fully. It will make it crank easier and start quicker if you do have a little air in the system.

 

The original water separator was non-serviceable, and prone to failure, so most times it is bypassed, and the only filter was the one mounted on the passenger side of the motor behind the alternator.

 

The last time I tried to drain the water from my OEM water separator, the plastic parts disintegrated in my hand. The truck was then not yet 20 years old. I bought a Racor all-in-one filter & water separator unit, and installed it in place of my OEM filter, in the location you just mentioned.