What size is my fuel tank?

[Thesiger]

On my 90' suburban I'm trying to figure out my tank size for helping calculate my mpg, but I cant figure out if its a 36, 38, 40 or something else. is there a definite way of telling?

 

[nvrenuf]

I always thought there was only 2 tank choices for a Sub - 31 or 40 gal. I have never seen a Sub with a 31 gal tank so I believe the 40 gal is by far the most common.

As for determining the size;

1) Run the truck until the tank is close to empty, if it takes significantly more than 31 gals you have a 40.
2) If you still have the RPO sticker in the glove box you can google each of the codes to see if one identifies the tank.
3) Check parts sites (like Rockauto) and see if they list the dimensions for a new tank and compare that to yours.

 

[hoagster]

And you really don't need to know what size tank you have to calculate mpg! Just figure out how many miles you have driven since the last fill up then divide it by how many gallons you pump in since your last fillup.

 

[Thesiger]

I'd still like to figure it out for other reasons, When I filled it up to the max it was leaking out of the top! So some replacement parts may be in order.

 

[Thesiger]

On the dash its marked "suburban SLE" if that's any indication.

 

[Bextreme04]

On my 90' suburban I'm trying to figure out my tank size for helping calculate my mpg, but I cant figure out if its a 36, 38, 40 or something else. is there a definite way of telling?

A little more info would help. Also the SPID label in the glovebox would tell you. Is this a 1500, 2500? Is it gas or diesel?

Either way, you could only have a 31 gallon or 40 Gallon tank.

Get your measuring tape out and climb under the back of the burb.

31 gallon is 12.75" tall and 28x28" square
40 Gallon is 13" tall and 35 x 28" rectangle

 

[HotWheelsBurban]

A little more info would help. Also the SPID label in the glovebox would tell you. Is this a 1500, 2500? Is it gas or diesel?

Either way, you could only have a 31 gallon or 40 Gallon tank.

Get your measuring tape out and climb under the back of the burb.

31 gallon is 12.75" tall and 28x28" square
40 Gallon is 13" tall and 35 x 28" rectangle

Most Burbs had the 40 gallon, IIRC. All 5 of ours did, 2 that were big block and 3 that were 350s. And that's a ginormous sob especially when you have to hang a trailer hitch around it. Dad and I did that on our '79 cause it didn't have one and we needed to tow our utility trailer. Quality aftermarket unit, Valley I believe, supposed to go on in an hour and it took all day....

 

[Wannabe]

You can be positive by multiplying length,width, and height, take that total and divide by 231.The answer will be the capacity of your tank.

 

[Hunter79764]

FWIW, my 87 3/4T base model at best has a 31 gallon, but I think it's a 25. Rock auto has all 3 options as replacements. I haven't run it dry completely to test, but the most I've put in was about 22 gallons or so.

Based on dimensions on Rock Auto, the 25 gal is 10.75" tall x 28x28, the 31 is 12.75" tall x 28x28 and the 40 is similar height to the 31 but 28x35".

 

[Thesiger]

It's a gas 350 V1500, I'll go out and measure it now. Issue now I found totally separate from this is that the tank leaks a ton out of the top when I fill it up! Sender unit or seal? More $$$ either way...

 

[Bextreme04]

It's a gas 350 V1500, I'll go out and measure it now. Issue now I found totally separate from this is that the tank leaks a ton out of the top when I fill it up! Sender unit or seal? More $$$ either way...

Its just a rubber O-ring up there under the sender. Not usually a leak spot. It could be just a loose clamp or a tear in the filler hose or vent hose.

 

[Thesiger]

I watched it as I filled it the last time, and it really blows out from around the unit, makes little gazers then runs down the sides of the tank. I bought I seal already. someone's already cut a hole in the floor over the tank so that helps.

 

[SquareRoot]

SLE just means "Soon to be Low then Empty". Comparing the actual dimensions to the dimensions given for new tanks will tell what the "design" capacity is. If you want to know the "actual" capacity, run it empty then fill it up. It's a worthwhile exercise as you will discover it holds more than stated and X amount of fuel doesn't exactly correspond to what the gauge says. When I installed my new tanks and senders for EFI, my gauge never moved to empty until I poured 5 gallons in. It showed full at 20 gallons but still took another 3 gallons. Fortunately, my Dakota Digital lets me calibrate it to read the level exactly from empty to full.

 

[Hunter79764]

Being EFI, they really need to have some fuel in them for best pump life, and I suspect GM's rating of tanks was a little more conservative on the early EFI to account for it.
I went the opposite direction from SquareRoot on my wife's daily. She liked to run it lower than it should, to the point of me having to rescue her with a 5 gallon can a few times. With HPTuners, I adjusted it to read a couple gallons lower without her knowing, and we haven't had issues since. The speedometer is also a few MPH fast to help on the speeding tickets...

 

[oldretiredafguy]

Being EFI, they really need to have some fuel in them for best pump life, and I suspect GM's rating of tanks was a little more conservative on the early EFI to account for it.
I went the opposite direction from SquareRoot on my wife's daily. She liked to run it lower than it should, to the point of me having to rescue her with a 5 gallon can a few times. With HPTuners, I adjusted it to read a couple gallons lower without her knowing, and we haven't had issues since. The speedometer is also a few MPH fast to help on the speeding tickets...

Little technique I taught my wife while we were living in W. Germany in the mid 80's: if the tank is at half consider it empty. If you slide off a road during a snow storm, a half tank will keep the Mercedes 6 banger idling for several hours, to provide heat. We also carried MRE's, blankets and water in the trunk. She still does that to this day!