Which gas tank is main tank? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

bodyman922 · 08-02-2015, 12:02 PM

My 78 GMC needs a new gas tank sending unit. When I look on rock auto's website they have a few different brands to choose. Most list if they are for drivers or passenger side except for the dorman ones, they list for either main or auxiliary tank. My questions are which tank is main and auxiliary tanks? Is there a certain brand of sending unit that is preferred; spectra premium, dorman, or other? Thanks for the help.
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old yelr · 08-02-2015, 01:18 PM

Driver side is the main tank and passenger side is auxilliary.

**Corts60** · 08-02-2015, 03:13 PM

Quote:

Originally Posted by old yelr

Driver side is the main tank and passenger side is auxilliary.

Incorrect. I have had 5 square bodies with dual tanks and all main tanks were passenger side or RH tank.

mnz28 · 08-02-2015, 03:19 PM

Passenger side has the shortest distance to fuel pump.

ElGracho · 08-02-2015, 06:05 PM

Quote:

Originally Posted by Corts60

Incorrect. I have had 5 square bodies with dual tanks and all main tanks were passenger side or RH tank.

Not so fast.
1973-1980 a single tank would have been on the passenger side.
1981-1987 single tank is on the drivers side.

The optional second tank is the "auxiliary tank" by the sales and service documentation so that means the "main tank" matches what the factory installed when they only installed one.

chengny · 08-03-2015, 01:07 AM

2X ElGracho. Up until 1980 the main fuel tank (correctly called the production tank) was located on the RH side. If the truck came with the dual tank option, it was equipped with another tank (called the auxiliary tank) which was located on the LH side.

In dual tank applications, the RH tank was the default tank. It would be the tank that supplied the fuel pump if no power was applied to the tank switching solenoid.

Note the tank designations in the wiring diagram below. It is for a pre-1981 dual tank application:

In 1981 the LH tank became the main/production tank and the switching circuitry was changed from a single wire system to a 5 wire system:

Keith Seymore · 08-03-2015, 07:15 AM

Quote:

Originally Posted by ElGracho

Not so fast.
1973-1980 a single tank would have been on the passenger side.
1981-1987 single tank is on the drivers side.

The optional second tank is the "auxiliary tank" by the sales and service documentation so that means the "main tank" matches what the factory installed when they only installed one.

x3.

Primary tank was RH originally; became the LH tank after the front end refresh.

K

old yelr · 08-03-2015, 09:58 AM

I was looking at 81-87 trucks when I answered that.

bodyman922 · 08-03-2015, 07:48 PM

Thanks for all the reply's. I thought it was the right tank but just wanted to be sure. I ordered a dorman one from rock auto so now I should have a working gas gauge again. I went with the dorman one because it showed a lifetime warranty and all the others were only 1-3 years. I figure it's worth the extra cash not to have to drop the tank again.
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08-02-2015, 12:02 PM	#1
bodyman922 Registered User Join Date: Apr 2011 Location: Minnesota Posts: 38	Which gas tank is main tank? My 78 GMC needs a new gas tank sending unit. When I look on rock auto's website they have a few different brands to choose. Most list if they are for drivers or passenger side except for the dorman ones, they list for either main or auxiliary tank. My questions are which tank is main and auxiliary tanks? Is there a certain brand of sending unit that is preferred; spectra premium, dorman, or other? Thanks for the help. Posted via Mobile Device

08-02-2015, 01:18 PM	#2
old yelr Registered User Join Date: Nov 2011 Location: Winnipeg, Manitoba Posts: 164	Re: Which gas tank is main tank? Driver side is the main tank and passenger side is auxilliary.

08-02-2015, 03:19 PM	#4
mnz28 Registered User Join Date: Jun 2006 Location: wi Posts: 16	Re: Which gas tank is main tank? Passenger side has the shortest distance to fuel pump.

08-03-2015, 01:07 AM	#6
chengny Registered User Join Date: May 2007 Location: New Hampshire Posts: 349	Re: Which gas tank is main tank? 2X ElGracho. Up until 1980 the main fuel tank (correctly called the production tank) was located on the RH side. If the truck came with the dual tank option, it was equipped with another tank (called the auxiliary tank) which was located on the LH side. In dual tank applications, the RH tank was the default tank. It would be the tank that supplied the fuel pump if no power was applied to the tank switching solenoid. Note the tank designations in the wiring diagram below. It is for a pre-1981 dual tank application: In 1981 the LH tank became the main/production tank and the switching circuitry was changed from a single wire system to a 5 wire system:

08-03-2015, 09:58 AM	#8
old yelr Registered User Join Date: Nov 2011 Location: Winnipeg, Manitoba Posts: 164	Re: Which gas tank is main tank? I was looking at 81-87 trucks when I answered that.

08-03-2015, 07:48 PM	#9
bodyman922 Registered User Join Date: Apr 2011 Location: Minnesota Posts: 38	Re: Which gas tank is main tank? Thanks for all the reply's. I thought it was the right tank but just wanted to be sure. I ordered a dorman one from rock auto so now I should have a working gas gauge again. I went with the dorman one because it showed a lifetime warranty and all the others were only 1-3 years. I figure it's worth the extra cash not to have to drop the tank again. Posted via Mobile Device



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