fuel heater only works with the key in run position.
it is also not really needed, imine has been disconnected since it shorted out back in 1990. and i have never had any issues with fuel gelling. and i have seen 10 below zero a few times.
the trick is to run GOOD fuel. if i know it is going to be cold, i will add some howes to the tanks.
and yes, you can replace just the cable for the block heater
here is a three pin push on plug that should fit your truck for $28:

 

I use Shell Diesel and I occasionally use the Ford Powerstroke fuel additives one is for lubricity and Cetain booster the other is a Cetain booster and antigelle. I will add both if i know its going to be extremely cold otherwise i run the one with Cetain booster and lubricity modifier. The truck definitely starts and runs better with the Ford additives than without and has more power. Another question i have what kind of mpg can be expected from one of these trucks? The additives definitely increase the distance i can go between filling both tanks.

 

Mpg? I think I get 12 in the 87. If you had a turbo, you'd do better. Definitely add Powerservice , diesel extreme , 2 stroke oil, whatever when you fill up. The pump will last longer. If it's starting in 15 degree weather with no help, you're way ahead of the game. That tells me no air intrusion. Celebrate by getting one of those smelly green trees for the truck.

 

if you get 13-15 consider it good.
back when i got my 88 and diesel fuel was over 60 cetane, i would regularly get over 20 mpg on the road and 17-18 around town.
now the cetane rate is 40 (if we are lucky) i average 12-14 on the road and 9-10 around town.

 

When I was running WMO even though it had lower cetane, I gained 1mpg, my guess is the extra btus since it's more dense.

The biggest factor to fuel milage is how much your right foot stomps that skinny pedal

 

I use shell diesel and the Ford fuel additives i noticed the engine runs smoother and stronger with them also since both tanks work my range driving conservconservatively is about 350 to 400 miles if I stay out of the skinny pedal otherwise 290 is what I see. Yes both tanks work flawlessly. The front one is like 30 gal I think and the back 15 or 20 I cant remember. I believe I should be getting more than that.

 

only IF someone changed the tanks

 

the rear is original to the truck the front has been replaced the skid plate is missing. Question is how many gallons are they and is my range good bad or somewhere in between?

 

yup. both tanks from factory are rite around 19 gallons.

 

one is way bigger than the other. The one on the driver's side frame is huge. Its about 3/4 the length of the bed which is the longest box available at the time it seems. I will post a picture here in a bit of it.

 

 

 

 

total capacity in 91 was like 37.2 Gal the front tank is larger than the rear tank 19 in front 18 in rear same as my 93 on the shorter truck the front tank was 16


SO what TJC says is correct for all practical purpose

 

ok so is the range I see good for running both tanks or should I be seeing more?