Why so many tanks and how to clean them?

[Syco67]

My sisters 69 GMC 3/4 ton 2wd has 3 gas tanks on it, was that a factory option, or an aftermarket deal? There is a selector valve on the floor between the driver door and the seat. The PO said he only ever used the middle tank because he was unsure of the condition of the other 2. How should we go about checking those tanks out, put in some gas, some cleaner, and see what happens? I know they are empty, I opend the valve, and nothing came out, not even a trickle.

[bigvinnie]

I think there's a thread that describes a process where you remove them and take em to a radiator shop to be boiled out, then treat em with a petroleum resistant coating that you pour in and swish around in the tank and let dry.... probably available from Eastwood or some place similar... maybe someone has done this and can comment on it...???

[Longhorn Man]

No need to boil them out onless there is thick coat of crap/corrosion in there. All you really need to do is drop the tanks, and have them steam cleaned untill the smell of fuel is gone. (one to 3 hrs avererage) This will also remove almost all of the rust, even scaley rust if you blast it directly. If you have access to a steam cleaner, you can do this for no charge, I think our rad shop charges about 50 bucks to do this.
A coating pourd in like the POR15 kit is a very good idea, otherwise, it will rust again.
As for originality of your tanks, if it is listed on the option sheet, then they are factory installed. However, most were dealer installed, or owner installed.

[mrein3]

Originally posted by Syco67
My sisters 69 GMC 3/4 ton 2wd has 3 gas tanks on it, was that a factory option, or an aftermarket deal? There is a selector valve on the floor between the driver door and the seat. The PO said he only ever used the middle tank because he was unsure of the condition of the other 2. How should we go about checking those tanks out, put in some gas, some cleaner, and see what happens? I know they are empty, I opend the valve, and nothing came out, not even a trickle.

To answer the question as to why so many, drive across country and see how far you get on one tank.

I have a saddle tank that the PO used before I bought the truck. It leaked when I got it. He said he just used it first and ran it until it was dry. I didn't use it for a couple of years then found myself where you are. I didn't know the condition of the tank and I was afraid to use it.

I brought it to the shop I used to work at. They sent it out to their radiator shop. There they "boiled it out", soldered the leak, and coated the inside. It cost me $50. I don't know what boiled it out means but I'm assuming it means steam cleaning.

While I had the tank out I installed a fuel gauge sender from JC Whitney in the tank. The gauge I mounted knee knocker style under the dash.

I nearly doubled my range with the approximately 17 extra gallons of fuel. It just sucks to fill them both up $s wise.

[da-burb]

I had the 3 tanks in my first truck too. Behind the seat you have 21 gallons, on the drivers side I had 18 gallons, and the passenger side held 16 gallons. At 10 mpg I could travel 550 miles between fill-ups. And I needed everry gallon I could carry on my trips to Canada.

If you need the extra capacity, but not 3 tanks worth. You might want to consider dumping the 30+ year old tanks and install a blazer/suburban tank at the back of the truck. A new re-production tank can be had for $200+/-.

[Longhorn Man]

Boiling the tank out involves dropping it in a very nasty caustic chemical, and soaking it for a while...I've seen rads go in the tank for 2 hrs at a time.

[trukman1]

Syco67, not meaning to highjack your thread but I did some inquiries into this recently. I too have a set of old side tanks and decided to take them to the radiator shop (not done yet). However, I'm missing the manual switch on the floor. If you decide not to keep or use all three tanks would you be interested in selling the switch. I have an electric switch for 2 tanks that I'd be willing to trade if interested. Good luck. Thanks

[Edmond]

My Longhorn was also originally with 3 tanks. The two saddle tanks were the plastic ones, so I presume they were dealer installed? (It's not on the option list in the glove box)
According to the assembly manual the factory ones are metal.
I did have the switch on the floor like you have.
Since I run on propane I only have one saddle tank left for emergency only.

Cya,
Edmond

[Longhorn Man]

Actually if you have plastic/poly tanks, these would be more modern. I don't think poly was DOT certified untill the early 80's.

[Edmond]

That sounds logical. I always wondered if they had plastic/Poly tanks in those days. :-)
Would there be a date stamped on the tanks perhaps?
I will check when I get home.

Cya,
Edmond

[Longhorn Man]

No idea honestly. The only time I ever drop tanks, there is normally lots of cussing involved.

[Edmond]

Did not find any date stamped on the tanks....
So there is no way of telling when these were put under the truck.

Cya,
Edmond

[Goat Farmer]

I was wondering about that switch, since I have one on my dash. What does it mean? does the one on the floor do anything if you have 2 tanks and switch on the dash?
sorry to hijack this

[trukman1]

Goat Farmer, I'm thinking you might be describing an electrical switch where the actual toggle is on the dash with a solenoid operated valve underneath? The one that was factory installed was a manual switch in the floor that didn't require any other switch. I just got one today from "fine 69" and he showed me how it worked...spring loaded detents with a manual lever. Hope this helps. Trukman1

[68cajun]

I have the saddle tanks on the 71 i have and they appear to be made of some type of fiberglass.