Single tank to Dual tank - The 1947 - Present Chevrolet & GMC Truck Message Board Network

mattshea125 · 02-22-2021, 01:24 PM

Hey everyone. I have a 1978 K20 and was looking for some information on adding a fuel tank to a single fuel tank truck. I have a bed from a dual tank truck and would like to add another 20 gallon fuel tank. The truck does not have any of the wiring, switch, or transfer valve. I would like to stick with the factory switch and transfer valve if possible. Any information from someone who has already done this would be much appreciated. Thanks

**hatzie** · 02-22-2021, 01:55 PM

You should be able to install the 1981-1991 dual tank system.
The valves for the 1973-1980 system are made of unobtainium now.

The filler necks are different diameters after 1980. If the bed is from an 81-91 truck with the 81+ filler necks get tanks that mate with the fillers.

The dual tank theory of operation thread should help.
Post #2 is the 81-91 system. Ignore the TBI fuel pump info.
http://67-72chevytrucks.com/vboard/s...d.php?t=754061

02-22-2021, 01:24 PM	#1
mattshea125 Registered User Join Date: Jan 2008 Location: Riegelsville P.A Posts: 38	Single tank to Dual tank Hey everyone. I have a 1978 K20 and was looking for some information on adding a fuel tank to a single fuel tank truck. I have a bed from a dual tank truck and would like to add another 20 gallon fuel tank. The truck does not have any of the wiring, switch, or transfer valve. I would like to stick with the factory switch and transfer valve if possible. Any information from someone who has already done this would be much appreciated. Thanks

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02-22-2021, 01:55 PM	#2
hatzie Moderator Join Date: Oct 2008 Location: Wentworth, NH Posts: 4,977	Re: Single tank to Dual tank You should be able to install the 1981-1991 dual tank system. The valves for the 1973-1980 system are made of unobtainium now. The filler necks are different diameters after 1980. If the bed is from an 81-91 truck with the 81+ filler necks get tanks that mate with the fillers. The dual tank theory of operation thread should help. Post #2 is the 81-91 system. Ignore the TBI fuel pump info. http://67-72chevytrucks.com/vboard/s...d.php?t=754061 __________________ 1959 M35A2 LDT465-1D SOLD 1967 Dodge W200 B383, NP420/NP201 SOLD 1969 Dodge Polara 500 B383, A833 SOLD 1972 Ford F250 FE390, NP435/NP205 SOLD 1976 Chevy K20, 6.5L, NV4500/NP208 SOLD 1986 M1008 CUCV SOLD 2000 GMC C2500, TD6.5L, NV4500 2005 Chevy Silverado LS 2500HD 6.0L 4L80E/NP263 2009 Impala SS LS4 V8 RTFM... GM Parts Books, GM Schematics, GM service manuals, and GM training materials... 1973-1991 GM Light Truck Service, Unit/Overhaul, Wiring Manuals, Parts Books and Some 1968-1999 GM Service Training textbooks in PDF 1988-1998 GMT400 CK service manual project 1988-1993 GMT400 CK parts books. 1967-1972 GM Light, Medium, & Heavy Truck Service Manuals in PDF Please include at least the year and model in your threads. It'll be easier to answer your questions. And please let us know if and how your repairs were successful.



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