If you get a 22 gal tank it WILL NOT show from the outside of the car. It is just slightly higher in the trunk. Just comes up to level with sides (inside) of trunk. Did it in a 68.

So....the 22 will fit a 65 coupe? I have been thinking of going to a bigger tank

From my memory, the '69 tank (which I have) is 20 gallons and the '70+ tank which is 22 gallons. As mentioned, you'll either need to modify your filler neck or buy the swap filler neck. To me, the loss trunk space is not noticeable.

Fastbackbhoy wrote:

Just trying to find out the fuel capacity in My 66Mustangs fuel tank

Is it 13 or 16 Gallon? and is there a bigger tank available??? I seem to remember reading that there is a slightly larger tank available and is it very noticeable from rear

just trying to work out MPG. And sort out the Erratic fuel gauge Never reads completely full ( when full is about 1/8 away from Full,and when completely empty only takes 11-12 Gallons to full usually which is a real pain trying to Guess how much is left, one of these days I'll just run it dry and have a gas can with Fuel in trunk ,

think I'll change to the 70 mustang with new sender and go from there I'm surprised no one makes a bigger tank for 1966 " will any 1979 fit or is it got me be model specific ie fastback etc


Jimmy O

 
The 66 had a 16 gal tank.  70's had 20 gals.  71-72's had 22 gal tanks.  All will fit your 66.  There is no difference between coupe, FB, & convertable tanks.  You must redo the filler neck as the 66 filler will not fit as is.  I would think someone would manufacture such necks by now.  I just did some cutting and used a gasoline capable hose.  Several in this site have done it who may have a better solution than I.

Get the sending unit for the year of the tank.  All years are compatible with each other.  I have found that they are consistant, but inaccurate.  The 70 tank in my 66 has a 70 sending unit and it shows empty after 16 gallons.  That is better than showing empty after 12 gallons like it did when I used the 66 sending unit on the 70 tank.  Still not right. 

The intake pipe could be bent some to get the guage to be more accurate.  But be careful as it is copper (as I recall) and could split with a lot of work.  The joints are none too strong either.  The best way to test the sending unit is to cobble up a battery, fuel guage, sending unit, and tank.  Then you can test the whole thing outside the car and use water rather than gas for the liquid.  After a little cut and try, you could get it accurate.  You should also get a tank with a drain plug.

Just keep away from testing in the car with gas in the tank.  Very dangerous when transferring into and out of the tank.

josh-kebob wrote:

funny how JohnsMustangparts has a 22 gal listed for a '70.........but, hey wadda I know.........your results may vary........

Looking at Mustangs Unlimited and National Parts Depot, the capacities are:

65-68 = 16 gallons
69 = 20 gallons
70 = 22 gallons
71/73 = 20 gallons

Not that they are the be-all end-all...

Last edited by Jeff in GA (9/25/2013 6:21 PM)

I put a 69, 20 gal. In my 67 and it fit fine.  Little adjustment on filler neck, but that was it.  Inside trunk is a liitle higher from the tank, but I gained 4 gal.

On my 67 cougar I put the 69-20 gal tank in many years ago. I found that I had to cut the filler neck at the top about an inch from where it comes through the taillight panel. I cut a little at a time until I got the right curve, marker it with a Sharpie,washed  both pieces out and drove car to muffler shop, where he saw what I needed done. He then tacked it on a bench, we tested it after it cooled down, and he took it out and welded up for me. When I got home I sprayed it with galvanizing paint compound inside and out. Mustangs have a different curve to them than cougars, so it might be different for you as far as cutting. My 20 gal tank rusted out a couple of years ago, so I bought one of those stainless jobs, very nice. Found a place in Minnesota that sells them on eBay for about $200 with drain plug. The aftermarket filler neck hoses are complete crap that the mustang shops sell, so take your old one go to Napa or a marine shop and get a piece of filler neck hose or marine exhaust hose same size, which are heavier and reinforced. The mustang hoses now are thin and balloon out on a hot day....was the source of fumes in my trunk that I couldn't find a few months ago. Hope this helps