Fuel Tank Question

[Rifter_Chevy]

Hello all, i am new to your wonderful site but now that i own a chevy i will be around here alot im sure.

I just picked up a 1984 3/4 Ton 4x4 and have a few questions about fuel tanks.

It was originally a dual tank truck and has the switch and all the wiring for duals but current only has one 16 gallon tank installed on the passenger side.

I was wondering when i install a new 20 gallon on the drivers side will i be able to replace the current 16 gallon with a 20 gallon or am i going to find something that will stop me from doing this?

Also is there a good way to install Skid plates under the fuel tanks? Or perhaps a company that makes armored chevy saddle tanks for off road use?

EDIT TO ADD:

Its a long box

Thanks!

[tucsonjwt]

A long box should take two 20 gallon tanks - that was the stock set up. The previous owner may have had leaks on the dual tanks and just went with a single 16 gallon tank to save money. Also, there are a few components that could be bad: dash switch, switching valve, sending units, etc. You should not have a vapor recovery canister since you have a 3/4 ton, but you should check that - if you have one, you might have to replace that.
I don't know about skid plates for fuel tanks. If you are off roading this vehicle you may want to check with the off road guys for that info.
Here are some pics of my stock set up. Spare tire pic shows how I extended the vent lines to the rear of the truck to keep gas ordor/fumes out of the cab.

[Rifter_Chevy]

Thanks for the quick reply. The previous owner said the dash switch and valve worked when he uninstalled the second tank, hopefully they still do.

I do not have a vapor recovery cannister and it appears the single tank i have is a 2 outlet sending unit a feed and return line with no vent, not sure if thats good or bad.

Since i am running a 350 with a carb can i get away with 1 outlet senders and block the return line at the pump?

[parrisc19844x4_468]

Sorry Tuson, but I bought my 1984 4x4 new and it had 2 16's from the factory.


Rifter, When I put on a 20 it messed up my gas gauge, so I went back to a 16.

Regards

[tucsonjwt]

I don't know about blocking off return line, but the dual tank configuration is set up for a return line. Maybe you can use the 16 gallon tank if it is clean and not leaking and install a 3 outlet sending unit, like a stock 20 gallon tank. I'm pretty sure you need a vent line, otherwise you will have pressure buildup in the tank, unless you get a vented cap which I think is not legal anymore.
A word about sending units. The aftermarket sending units (like Spectra brand) will cause the fuel gauge needle to bounce when you accelerate, turn corners, stop, etc. The gauge will still be accurate, just bouncy. The stock AC/Delco unit will not do that, but it costs about $160-$180 per unit vs. about $45 per unit for the aftermarkets.

[joe231]

Originally Posted by parrisc19844x4_468

Sorry Tuson, but I bought my 1984 4x4 new and it had 2 16's from the factory.

long beds also came with 16 gallon saddle tanks

Originally Posted by parrisc19844x4_468

Rifter, When I put on a 20 it messed up my gas gauge, so I went back to a 16.

Regards

the size of the tank has nothing to do with the gauge. how was your gauge messed up?
as long as you have the correct 0-90 ohm sender it should work fine.

Rifter, I believe the 20 gallon tanks will bolt right up and I know they use the same gas tank brackets and straps as the 16 gallon tanks.

[tucsonjwt]

I learn something every day. I thought 20 gallon tanks went on long beds and 16 gallon tanks went on short beds.

[Rifter_Chevy]

Well i am going to buy a single 20 gal and start from there then think about replacing the current 16 if i can get the second working fine.

I just found it and i have a 6 port switching valve, this means i will need to use a 2 outlet sending unit in the new tank right(or 3 i guess with one port being a vent)?

[tucsonjwt]

I'll leave that question to the other posters, since it seems I do not have a stock set up after all.

[parrisc19844x4_468]

Originally Posted by joe231

long beds also came with 16 gallon saddle tanks


the size of the tank has nothing to do with the gauge. how was your gauge messed up?
as long as you have the correct 0-90 ohm sender it should work fine.

Rifter, I believe the 20 gallon tanks will bolt right up and I know they use the same gas tank brackets and straps as the 16 gallon tanks.

Thanks Joe for pointing that out, it makes sense. When I had the 20 gallon tanks on, the gauge would go way past full then only go to about 1/2 when empty. When I put the 16 back on it worked again. Maybe I had the wrong sending unit in, as I got the sending unit with the tank.

Rifter, the tank will go in, actually there are different holes on the frame for the 20 gallon tank because one of the brackets will line up different. Also the fill tube will be shorter for the 20 gl. if you shorten, you can't add on to it when you got back to a 16.
IMO, you are better off with 2 16's then one 20.

Been there done that.

[Rifter_Chevy]

Well ideally i want 2 20's

Plan as of right now is add a 20, get it working with the current 16 then pull the 16 and upgrade it to a 20.

Then if i still need more capacity im going to cram a blazer tank under the rear of the box.

Considering im going to daily drive this thing and my old car was a honda CRX im really really noticing the(frekking massive) lack of fuel economy and range. At least if i get 2 20's working i can fill up once every payday instead of twice a week like i am now.

[parrisc19844x4_468]

Originally Posted by Rifter_Chevy

Well ideally i want 2 20's

Plan as of right now is add a 20, get it working with the current 16 then pull the 16 and upgrade it to a 20.

Then if i still need more capacity im going to cram a blazer tank under the rear of the box.

Considering im going to daily drive this thing and my old car was a honda CRX im really really noticing the(frekking massive) lack of fuel economy and range. At least if i get 2 20's working i can fill up once every payday instead of twice a week like i am now.

I would have to stop at the bank and get a loan to fill 2 x 20's

[Rifter_Chevy]

Originally Posted by parrisc19844x4_468

I would have to stop at the bank and get a loan to fill 2 x 20's

Lol the only reason i even bought a truck is because my commute to work is only 9 miles each way and i only work 3 or 4 days alternating each week so its not so bad.

Still missing the CRX though when im filling up.

[James McClure]

My dual tank system came from the factory at 20 gallons each side. Took a while to get each side working correctly during the restoration. As far as adding a third tank out back, I don't think thats such a good idea. Asside from the plumbing nightmare, you have sender wireing to deal with. Then you have to think about the spare tire and where to put it. Then there is the weight of an additional 20 gallons of fuel you'll be carrying (about 120 pounds) add that to the 240 you already are carrying and it's up to 360 pounds, and that's going to hurt mileage. I get 17 MPG with mine on the highway with a full load (3\4 ton and fully gassed up with a 350 quad) IF I am VERY gentle on the gas. If I am pulling my trailer fully loaded it drops to just over 14 MPG. Mind you I am talking flat lands and 55 MPH here. You should do fine with the 2 20 gallon tanks. jim

[rayfinseats]

My 83 has dual tanks and factory skid plates under them. I don't know how well they work but it was a factory option.

[James McClure]

Mine had those too. I think it came with dual tanks but I'm not positive. When I did the restore I took them off. Problem with the factory covers are they fit to close to the tank and they have no drainage holes or vents to let the water that gets in to wash the dirt\sand\salt out & you all know what happens then. I don't have any pictures yet of how I set up the running boards to cover the tanks and leave room to get in there to wash it out. When I get pictures I'll post them up. jim

[tucsonjwt]

If you are talking about the plastic covers on the bottom of the tanks at the front, my tanks have them also. They don't look like they would add too much protection to me, but I did see scuff marks on them.