I have an 81 F150 with a 351M and a C6 wit dual tanks

I'm not sure what size my front gas tank is, im getting ready to change out my sending units and on the front take i have the option of a 16gal tank or 19gal tank at the parts store. Does anyone know what these 81's came with?

Josh

 

According to my little 1982 truck manual it depends based on the bed length. Short or long.

 

Its a short bed.

 

You should really get yourself an Owner's Manual, Josh.

They're pretty cheap on eBay....
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You can't completely go by the owners manual, always measure the length of the tank if you are unsure of the origin of the truck. I still run into long bed trucks that were "fleet" vehicles that have 16 gallon tanks. If it is @ 60" long then it is a 19 gallon tank, if it is @ 42" long it is the 16 gallon tank. Ford loved to do crazy stuff on fleets... Anyone remember the 4cyl Taurus?

 

That's good to know, i'll have to check mine. I have never fit more than 15 gallons in the front tank.

 

Due to the sump in the sending unit, half a gallon is not used. So with a 16 gallon tank, only expect to burn a maximum of 15.5 gallons... Then another half a gallon could be air space at the top. Although I have seen people top off their tanks past the automatic shut off. (Which is ilegal in California by the way.)

As for telling if the truck was complete when it left the plant that is simple enough...

The third digit of the vin number...

If it's a complete vehicle it will have a letter "T" and should be factory correct for parts.

If it's not complete, as built for fleet vehicles it will have a letter "M" for multi purpose, a letter "D" for incomplete vehicle, or letter "C" for stripped chassis. This is where you start to get into trouble for non typical factory accessories and parts such as odd ball gas tanks.

There are other ways to tell if the truck isn't normal factory equipped by looking at the DSO codes on the safety certification lable. Normally the district and DSO code would have the first two letters of the sales office the truck was sold to. IE: #"76" for Denver. For special fleet vehicles the first numbers would be #"83" for Government, #"84" for home office reserve, #"85" for American Red Cross, #"86" for recreation vehicles, #"87" for body company, #"89" for Transportation services, (Gillig school busses in Hayward california bought a lot of Ford cab and chassis products to make school busses for example. Most of these were E-series vans, or F-series mid-duty chassis with just the front fenders and hood without the cabs etc), then to finish off you got your #"90" export, or #"00" for special.

Those you would also have to watch out for. Other than that, if they were bought and sold through the dealer, you don't have much to worry about on non standard parts.

 

Where do you learn all this stuff?

Man, you're amazing sometimes.

It is things like this that are why I sometimes refer to you as an "industry expert."

The Powers That Be won't let me rep ya, though.

 

You guys are awesome!

 

Thanks for the compliment. I can only take credit for reading the information though,

The Ford Literature I have has all that information. The DSO (District Special Order or District Sales Office) codes along with the first two digit code can have a 6 or 8 digit code after the first two digits if special ordered. This code has information about your specific truck in the FoMoCo records as well. Theoretically a researcher can look up those codes and find the sales records for your specific truck, what dealer bought it, what special notations if any exist etc... which is more comprehensive than even a build sheet you get through Ford or Marti just using the vin. Sadly most of that info is lost.