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Old 09-08-2019, 11:04 PM   #1
SunSoaked
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Dual Fuel tank capacity?

Is there a code on the SPID that denotes the capacity of the saddle tanks?
85 K20. I assume it's 16 gal but since installing my Dakota Digital guages it's seems to be off about a quarter tank when below full. For instance, when it hits 1/4 tank, I fill it up and it takes 15 gallons.
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Old 09-09-2019, 12:13 AM   #2
dmack91
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Re: Dual Fuel tank capacity?

Not sure on the spid, but my 83 K20 has dual 20 gallon tanks.
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Old 09-09-2019, 06:00 AM   #3
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Re: Dual Fuel tank capacity?

Short of running it dry and refilling it, how do you know that?
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Old 09-09-2019, 07:06 AM   #4
Keith Seymore
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Re: Dual Fuel tank capacity?

Nope. Capacity is not noted on the SPID.

K
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Old 09-09-2019, 10:46 AM   #5
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Re: Dual Fuel tank capacity?

all short bed trucks used 16 gallon tanks, not enough room physically for a 20 gallon tank.

you can measure the tank, a 20 gallon tank should be roughly 56 inches long and be almost touching the front rear spring hanger. a 16 gallon will be roughly a foot shorter...43 inches if i remember.
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Old 09-09-2019, 11:22 AM   #6
sweetk30
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Re: Dual Fuel tank capacity?

0-90 ohms is the gm sender spec when they work in a perfect world .


and short bed tanks in a long bed get special filler tube steel pipe extension or if someone else swapped them in it would be a looooong rubber hose to reach the tank from the filler .
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Old 09-10-2019, 10:15 AM   #7
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Re: Dual Fuel tank capacity?

Fuel gauges are always just an approximation. On one side, filling from the half tank mark it will take ~11 gal, and the other side it is about 9 gal on my truck.
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Old 09-10-2019, 10:36 AM   #8
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Re: Dual Fuel tank capacity?

^^ This. On my 75, with the original gauge, I had 4 gallons left on E. Had to replace the gauge. Now E pretty much means expect to switch tanks real soon. Same tanks and senders. On a tank that is run dry, I can sometimes get as much as 21 gallons into the nominal 20 gallon tank.
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Old 09-10-2019, 10:50 AM   #9
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Re: Dual Fuel tank capacity?

Thanks for the info.
So is it safe to assume that shortbeds have 16 gallon tanks and longbeds have 20 gallon from the factory UNLESS someone swapped the shorts into the longbed?

I'll probably intentionally run one tank out of gas on purpose and then go to the pump on the other tank. I'll fill it and notate what the guage says at each 1/4 mark and full. I just want it to be on my terms, not in the middle of the freeway.
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Old 09-10-2019, 11:11 AM   #10
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Re: Dual Fuel tank capacity?

1987 r/c-10 i parted out for the body was factory twin tank 16 gal on a long bed . had the factory extender pipes for the fillers .

so do NOT think long = 20 and short = 16 ........... or you will be surprised .

also this truck had 56" rear springs in a 1/2 ton . hangers were still factory riveted to the frame rails .
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Old 09-11-2019, 12:12 PM   #11
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Re: Dual Fuel tank capacity?

Quote:
Originally Posted by SunSoaked View Post
Thanks for the info.
So is it safe to assume that shortbeds have 16 gallon tanks and longbeds have 20 gallon from the factory UNLESS someone swapped the shorts into the longbed?

I'll probably intentionally run one tank out of gas on purpose and then go to the pump on the other tank. I'll fill it and notate what the guage says at each 1/4 mark and full. I just want it to be on my terms, not in the middle of the freeway.
I just run a tank until it is just about at E then switch tanks. I'll fill the empty tank when convenient. Keeps the gas fresh in the tanks. Plus the only place that has hoses long enough to reach both tanks is Costco so it is a pain to try to fill both at the same time.
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Old 09-11-2019, 01:00 PM   #12
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Re: Dual Fuel tank capacity?

I just want to know when it is actually about to run out by the guage. My Nissan goes another 100 miles when it hits E, my motorcycle runs out at 3/4.
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Old 09-11-2019, 01:15 PM   #13
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Re: Dual Fuel tank capacity?

Quote:
Originally Posted by SunSoaked View Post
Thanks for the info.
So is it safe to assume that shortbeds have 16 gallon tanks and longbeds have 20 gallon from the factory UNLESS someone swapped the shorts into the longbed?

I'll probably intentionally run one tank out of gas on purpose and then go to the pump on the other tank. I'll fill it and notate what the guage says at each 1/4 mark and full. I just want it to be on my terms, not in the middle of the freeway.
Almost.

Short bed will always be 16 gallon tank(s).

Long bed could be a 16 gallon tank (depending on GVW and other powertrain considerations) but will usually be 20 a gallon tank.

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Old 09-11-2019, 01:16 PM   #14
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Re: Dual Fuel tank capacity?

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Originally Posted by DieselSJ View Post
I just run a tank until it is just about at E then switch tanks. I'll fill the empty tank when convenient. Keeps the gas fresh in the tanks. Plus the only place that has hoses long enough to reach both tanks is Costco so it is a pain to try to fill both at the same time.
For a manual trans vehicle you can actually run them completely dry; switch tanks and it will catch and keep going.

I used to do that with my '80.

K
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Old 09-16-2019, 09:43 PM   #15
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Re: Dual Fuel tank capacity?

ive seen them only have one tank also just pointing that out. lb with a single 20 gal tank.
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Old 09-18-2019, 05:48 PM   #16
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Re: Dual Fuel tank capacity?

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Originally Posted by Keith Seymore View Post
For a manual trans vehicle you can actually run them completely dry; switch tanks and it will catch and keep going.

I used to do that with my '80.

K
I do this all the time in my 76, but it's an auto. Why the manual trans stipulation?
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Old 09-18-2019, 06:23 PM   #17
sweetk30
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Re: Dual Fuel tank capacity?

so you can coast the engine in gear and run the mech fuel pump . auto you would need to crank the engine until fuel gets up .
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Old 09-18-2019, 09:26 PM   #18
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Re: Dual Fuel tank capacity?

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so you can coast the engine in gear and run the mech fuel pump . auto you would need to crank the engine until fuel gets up .
Depends. Slushboxes will stay "in gear" for a short while.
If your engine stumbles and you switch tanks it may catch and keep going even with an automagic.
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Old 09-19-2019, 10:11 AM   #19
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Re: Dual Fuel tank capacity?

Automatics are evil! We had our first sub 100 degree summer day yesterday! That NV4500 sitting in my garage is begging me to jump in the truck.
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Old 09-19-2019, 12:14 PM   #20
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Re: Dual Fuel tank capacity?

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Automatics are evil! We had our first sub 100 degree summer day yesterday! That NV4500 sitting in my garage is begging me to jump in the truck.
I love my NV4500 behind my 454. Way better than the TH400 that I pulled out. Weather is finally to the "sleep with the windows open" time of year.
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Old 09-19-2019, 05:49 PM   #21
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Re: Dual Fuel tank capacity?

You will usually have several seconds of partial power before the motor really dies. It only takes a second or so for fuel from the full tank to reach the carb. As long as you are at cruise, you will feel the loss of power well before the engine fully dies. You don't want to be in the middle of a high power merge onto an interstate when a tank runs dry. Between the low fuel level and the high front to back slosh factor for these tanks, you can go from full power to off almost instantly.
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Old 09-20-2019, 02:22 AM   #22
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Re: Dual Fuel tank capacity?

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so you can coast the engine in gear and run the mech fuel pump . auto you would need to crank the engine until fuel gets up .
EFI so I don't have to worry about spinning the engine. I just don't like running the pumps dry, even for a few seconds.
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Old 09-20-2019, 09:37 AM   #23
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Re: Dual Fuel tank capacity?

I ran the tank as low as I dared and then let it idle in the driveway for 15 minutes until it ran dry and died. Swapped tanks and went to the gas station.
I put in 3 gallons and the guage still read empty. That's where I set my low fuel warning light on the Dakota VHX. Did I mention how much I love that DD VHX? Anyways, the 1/4, 1/2, 3/4 and full marks all correlated with the 20 gallon tank. It actually held 21.8 gallons to the top.
Now I know what I have and when the warning light comes on, I've got 30 miles to switch tanks or filler up........or walk...lol.
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Old 09-20-2019, 12:35 PM   #24
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Re: Dual Fuel tank capacity?

I recently put some NVU digital gauges in my 81 swb, when the fuel gauge hits 1/4 tank, I pull over at the nearest gas station. Earlier this year I actually ran out of gas when I decided the gauge was lying to me, and I just got one little 16 ga tank, so there was no switching for me.

I am guessing that it is more of an art than a science to get a digital set up to work with an analog sending unit and most of these companies figure close enough is close enough.
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Old 09-23-2019, 09:52 PM   #25
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Re: Dual Fuel tank capacity?

Seems to me, back in the 70's there was a rule? that stated GM could only put on 39 gallons worth of fuel tanks in any long bed pick up as a MAX capacity?

Maybe somebody can clarify this?
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