I know that living here in AZ I don't think I would ever use it but .... where is or where would the plug be on my 08 F250?

 

Is your truck gas or diesel? If diesel every truck has a block heater but not all of them have the plug to plug in. If gas it was an option. The actual heater is on the passenger side of the block on the engines. If you lay under your truck and look up at your starter you should see an orange wire that would be the wire going to your block heater. The plug is a black plug with a rubber cap, it should be somewhere tucked in on the passenger side engine compartment. Hope this helps.

 

Do they make block heaters for a 1998 F-150 5.4L?

It sure is slugglish to start mine with the temp. under 10.

 

my buddy has a 2000 or 01 and his 5.4 has a block heater

 

My first 08 F250 had the block heater cable and the plug was right behind the front bumper. My second 08 F250 does not have the cable, but all 08's have the block heater. You can buy the cable for less than $100, but I have heard that routing the cable from the block heater to the front bumper is a real pain. If you had a dealer install the cable, the labor would definitely cost more than the part.

 

I've been wondering if block heater might help with fuel economy .. I drive my 08 f150 4.6 a short distance <3 miles to my shop 2-3 times a day, everyday. My gas mileage averages 9-10 mpg.
I live in Houston where temps aren't cold and the truck is garaged at both my shop and home during the day. I figured the block heater might decrease the warmup time and rich fuel mixture.
I've noticed my wife's prius uses a thermos bottle to help maintain engine coolant at warmer temp to decrease warmup time.

 

Well Scruge, The Idea of prime mpg is achiving high combustion temp. You start getting your good gas mileage at about 225F. If you only drive less that 3 miles you'll really never achieve optimal temp or mileage! No a block heater won't really help you out a whole lot! But that's only my opinion!