Mil1on On your post (#13) in this thread you show a picture of your truck that you say has not been messed with.Your gas switch is labeled

AUX -on top
Main -on bottom

Then in post (#17) of this thread you say that when your gas switch **** is in the DOWN position your running off the front tank and when your switch is in the UP position your running off the back tank.

Your truck uses the switch just like my dual tank truck does and you've proven my point
In a dual tank set up the rear axle tank is cosidered the Aux tank and the frt tank is considered the MAIN
nuff said

 

No, Not Nuff Said ....

You're not understanding what I am saying.

read post # 27 again

My Quote: Not contradicating it all.

It's in the terminology.

You're presuming that the position of the **** means that tank that is being used.

ie: **** up means use AUX.. **** Down means uses MAIN Tank


But,Perhaps FORD is saying with the **** one direction OPENS the OTHER tank.

ie: **** DOWN shows AUX tank use...**** Up means MAIN Tank use.



I haven't proven your point.
You are assuming that the Fuel Tank **** Position is the actual tank in use.

What I'm saying is:

switch **** DOWN does NOT mean REAR Tank..It means Front tank (AUX) tank

switch **** UP means Rear Tank (Main) Tank




The Front Tank being the AUX - Mid-ship tank

The Rear Tank being the Main.


It's like someone reversed the Light switch in your bedroom.

switch UP usually turns the light ON

Switch down usually shuts the light OFF

In the Ford fuel tank switch it is maybe opposite.

Flipping the switch one way Opens the OPPOSITE tank to which the **** is placed.

 

Further to this discussion.

From the 1973 Owners manul

We already knew that the IN cab tank of those years was considered the MAIN tank

In the 1973 Trucks with dual tanks (In Cab and and what Ford calls Underbody tank.)


If your truck is equipped with the Optional underbody auxiliary fuel tank in addition to the Main tank,the fuel level in either tank is read by moving the the fuel gauge selector switch to the proper position (What does proper position mean in terms of which way the **** goes? )

Fuel flow is controlled by the tank selector valve mounted on the floor to the lewft of the driver's seat.

Illustration to follow.

 

Now even more specific info from the ford Owners manuals.

Btw, I have these Owners manuals,.

1973
1975
1977
1978
1979

and they all have different terminology and info.

You're going to love this next one from the 1977 book.

Trucks where the AFT tank is considered the Main Tank

1977 100/250 4x2
F350 138',140" and 155" WB

The AUX tank is the Midship tank.

Where the In Cab is considered the MAIN tank

1977 -150/250 4x2 RPO
F350 -136" 160" WB

1977 F150 4x4

Midship Tank is the AUX (except the F150 4x4 which is the AFT axle tank)

 

Ok....
Ill chime in on the tank issue now.....

On mine.... that switch on the dash is only to switch between which sending unit is sending the reading to the gauge....I have a valve on my floor with a labled plate stating which tank I am drawing fuel from....

Now then that being said...on my truck....the tank at the very back is the main tank and the tank closest to the cab is the aux. tank. I know this because I re did the fuel hoses one at at time myself and the fuel lines which corrolates to the aux. position on the valve I mentioned earlier go to that tank....and the line that corrolates to the main runs back to the very rear tank.

Originally mine was equipped with all three tanks seat...mid and rear but the seat tank was removed and those lines bypassed.

Long story short.....the aux. tank is the one closest to the cab in the box...and the main is the one closest to the tailgate. Just like in the diagram that Dennis posted from Ford. Anything other arrangement is most likely not stock and has been altered by a Previous Owner.
-Chris

 

Nollaig has not posted since the 21st. saying he would fill up the rear tank and see what happens. Main... aux...who cares as long as YOU know which tank the guage is reading on YOUR truck.
As to nollaig's original post, I can think of only two reasons the pump works on one tank and not the other.One,as mentioned before,a crack in the hose preventing suction from that tank.or just as likely,a faulty switching valve stuck on the front tank.
It's possible to be reading the guage for the rear tank but the valve is stuck on drawing from the front tank.
Am I missing something?

Don

 

well see it is important to lots of people and it causes discussion here every once and a while.

People need to know which tank is being used ....to which way the switch **** is positioned.

I will be scanning and posting the Owner's Manuals info sometime.

 

Hmmm I can't understand the logic of if the rear tank is the main why is it smaller than the middle? I recently acquired a 1978 c/s f250 and pulled the tanks today and assumed the bigger tank was the main. But I guess common sense is overrated! On that note I was on Lmc truck looking up tanks and they really didn't seem to show a duel tank option? Any suggestions where to start looking for a rear tank?

 

Rear tank is the main tank, mid-ship is the auxilliary. Here's a page from the ('73) Ford owner's manual.

 

From what I previously read on this thread it changed after 77? But I see that is a three page argument

 

LMC does have dual tanks, midship tank is on pg 38, rear tank is listed on page 39.
Page 39 also lists a 38 gallon rear tank.

 

Best argument offered is when a truck was ordered without an auxilliary tank, it came with the rear tank.

 

Sorry Mike, I hate to argue but 78's are special. These came right out of my '78 manual...

 

No need to argue, I stand corrected . That makes two new things I learned today.

 

and in '79 they marked them "Front" and "Rear"! (finally)