How many gallons can you put in your gas tank?

[Don-T]

My 73 K10 has dual 20 gallon tanks. I believe the truck originally has a single tank as there is not a factory mounted tank selector switch on the dash. It has a DPDT switch in a drilled hole. He switch did not work when I bought the truck but I rewired it. Now it switches properly and the gauge works with the tank that is selected. Both tanks are new 20 gallon capacity. When I run a tank down to empty on the gauge I can only put 13 gallons in to fill. Is that right or is there a problem with sending units or the gauge?

 

[Bextreme04]

My 73 K10 has dual 20 gallon tanks. I believe the truck originally has a single tank as there is not a factory mounted tank selector switch on the dash. It has a DPDT switch in a drilled hole. He switch did not work when I bought the truck but I rewired it. Now it switches properly and the gauge works with the tank that is selected. Both tanks are new 20 gallon capacity. When I run a tank down to empty on the gauge I can only put 13 gallons in to fill. Is that right or is there a problem with sending units or the gauge?

When I still had the dual tanks, I would run one down until it would sputter and then switch to the other.. then go to the gas station and fill the tank I just ran empty. It would usually leave ~3 gallons in the tank. I'd get about 17-19 gallons in it depending on the day. Now I have a single 31 Gallon and I never run it down to empty to see how low I can go.

 

[Don-T]

I have been thinking about doing that myself. I have a mechanical fuel pump so it shouldn’t be an issue. I would still like to know if this is normal or is there a problem. It doesn’t seem as though it would be this way. As far as iI know, the sending units for the 16 and 20 gallon tanks are the same.

 

[ali_c20]

Depends on how much $ I have. I suspect the sending unit ohms are not matching the gauge or ground of sending unit. Sending units for 16 and 20 gallon tanks are the same. Do what Bextreme04 mentioned and you will know.

 

[SirRobyn0]

When I still had the dual tanks, I would run one down until it would sputter and then switch to the other.. then go to the gas station and fill the tank I just ran empty. It would usually leave ~3 gallons in the tank. I'd get about 17-19 gallons in it depending on the day. Now I have a single 31 Gallon and I never run it down to empty to see how low I can go.

I think we all have a technique as to how we use the dual tanks. My Dad's truck as an example had a 20 D/S tank and a 16 PS, He hated filling both tanks, so he'd run off the DS tank only, unless he took it on a long trip. For me, because I run my truck a lot I definitely make use of both tanks. Fill both at the same time. Run DS until it's empty, I don't always go until it sputters, but I do hammer the gauge to E, flip over and run the right tank down around a 1/2 to 1/4 tank, then fill both.

I have been thinking about doing that myself. I have a mechanical fuel pump so it shouldn’t be an issue. I would still like to know if this is normal or is there a problem. It doesn’t seem as though it would be this way. As far as iI know, the sending units for the 16 and 20 gallon tanks are the same.

Yes, the 16 & 20 gallon sending units are the same there is a different right and left side, but one can easily adapt a sending unit to work in the wrong side.

To answer your first question there were only two factory tank sizes 16 & 20 gallon, but a number of configurations. Single tank trucks could be equipped with either a 16 or 20 gallon tank. And I thought my truck before I installed the second tank had a pathetic range with just one 20! Can you image a single 16 gallon tank? So the needle would be on E after using about 14 gallons (or less) so it would be at a 1/4 after using around 10! So then in dual tank trucks you could get one 20, one 16 or two 20's or two 16's I think two 16's were only available in short beds.

I personally would not go to a single rear tank as I would not want to reduce compacity, but I have considered add a rear tank and keeping my two saddle tanks.

 

[GTX63]

I have a 16 gallon tank in my 1980 GMC. It was a different time when commuting long distances wasn't the thing it is today. If you saw a 5 year old truck with 100k for sale you walked away; now we pay 50K for them. But yes, when the pump kicks off at 14 gallons I still smile a bit.

 

[scrap--metal]

So the needle would be on E after using about 14 gallons (or less) so it would be at a 1/4 after using around 10!

My fuel gauge needles don't come off full until I've burned at least 20% of the tank.

Old GM fuel gauges/sending units just aren't accurate. This is true for my trucks, Camaro, and Monte. You just have to know how each one behaves.

Regarding 20 gallon square tanks, I've run one out of gas in my K10 and couldn't put more than 18.7 gallons in it. I've also put over 19 gallons in my K20s tank. Both tanks were new 20 gallon replacements, but i couldn't say if they were the same manufacturer.

 

[Grit dog]

One thing I’m happy with is how WELL the gauge/senders work on the 86.
Both senders are likely original. I used the existing sender in one new tank I had to get.
Other than the gauge bounces a little with the gas sloshing. (There’s a fix for that, some resistor that goes in the dash, there’s a write up on here somewhere about it)
On the 86 with dual 20s, haven’t run one dry yet. But recently one was on dead E and not bouncing. The other barely above E.
Drove about 12-15 miles to the gas station on the one that started above E.
The emptier tank took 19.3gal and it was running on that tank when I started the truck at home. The other tank took 18.5.
Idk the actual volume of the tanks, but I get very close to, if not 20 useable gallons.

 

[SirRobyn0]

One thing I’m happy with is how WELL the gauge/senders work on the 86.
Both senders are likely original. I used the existing sender in one new tank I had to get.
Other than the gauge bounces a little with the gas sloshing. (There’s a fix for that, some resistor that goes in the dash, there’s a write up on here somewhere about it)
On the 86 with dual 20s, haven’t run one dry yet. But recently one was on dead E and not bouncing. The other barely above E.
Drove about 12-15 miles to the gas station on the one that started above E.
The emptier tank took 19.3gal and it was running on that tank when I started the truck at home. The other tank took 18.5.
Idk the actual volume of the tanks, but I get very close to, if not 20 useable gallons.

That's been able my experience. And that's how I know I need to switch tanks NOW when the gauge stops moving a little. Like you I can get more than 19 gallon in a truly empty tank. Which brings me to my next point, depending on how sensitive and what type of shut off is on the pump handle can make a differance. Some pump handles do not play well with older tanks and will leave a guy with less than a truly full tank.

 

[Grit dog]

^Dont even get me started about the damn vapor recovery nozzles.
F those things!
Curiously though, they seem to work perfectly with the squarebody fuel fillers. Now safety gas cans, the old CJ 5, the boat, the snomachines, are always a fight. Even the 99 Camaro is finicky.

 

[Keith Seymore]

Can you image a single 16 gallon tank?

Yes, I can.

K

 

[SirRobyn0]

Yes, I can.

K

Your not imaging it you own one! But your truck is a pretty unique configuration and I bet you get a far bit better mileage than most of us!

 

[SirRobyn0]

^Dont even get me started about the damn vapor recovery nozzles.
F those things!
Curiously though, they seem to work perfectly with the squarebody fuel fillers. Now safety gas cans, the old CJ 5, the boat, the snomachines, are always a fight. Even the 99 Camaro is finicky.

I fill gas cans, and I have a couple of 15 gallon portable tanks IDK what they are really called, but they are a cylinder that lays on it's side and has little legs to keep it from rolling and a gas pump handle. I should take a picture of one of them. Anyhow the vapor recovery nozzles are a PIA with those tanks. And I'm filling can or one or more of those tanks weekly, but once I get it to the farm I use the tractor to "mount it" at just overhead height in the overhang of the barn. After that it's easy to fill equipment from it.

 

[Steppin Razor]

Yes, I can.

K

Same. Previous owner replaced the 20 with a 16. I know the cheapest gas stations in all the neighborhoods I frequent.

 

[HotWheelsBurban]

Our '81 Sierra C15 had the dual 16 gallon tanks. To fill both I would have to get up in the bed and pass the nozzle and hose across, then get out and insert it into the filler. I understand why GM had them on both sides instead of both on one side like the contemporary ferds, but it sure is inconvenient when filling both tanks.