Dual Fuel Tanks Problem

[Gershwizzle]

So I got my '85 Sierra a few months ago and ran into a problem today. The truck originally had the 6.2 diesel in it, but a PO swapped in a 350 at some point. He then sold it to another guy who sold the truck to me. The PO I bought the truck from told me he had never used the left tank and wasn't sure if it worked. I have only been using the right tank as of this far, but accidentally put gas in the left tank today.

Is there anything that could go wrong if I try and use the left tank? I'm not sure if it's ever even had gas in it and now am worried that if I try and use it, it could mess up my engine.

Also, looking farther in the future, what would I have to do to make my left tank usable for gasoline?

Any help is appreciated

 

[FRANKENTRUCK]

So I got my '85 Sierra a few months ago and ran into a problem today. The truck originally had the 6.2 diesel in it, but a PO swapped in a 350 at some point. He then sold it to another guy who sold the truck to me. The PO I bought the truck from told me he had never used the left tank and wasn't sure if it worked. I have only been using the right tank as of this far, but accidentally put gas in the left tank today.

Is there anything that could go wrong if I try and use the left tank? I'm not sure if it's ever even had gas in it and now am worried that if I try and use it, it could mess up my engine.

Also, looking farther in the future, what would I have to do to make my left tank usable for gasoline?

Any help is appreciated

There is a distinct possibility that there is water mixed with rust in there . I would fuel up the other tank that you know works then take this to someone who can properly drain it .
The worst that could probably happen if you use that unused tank is the fuel filter would become clogged .

 

[89Suburban]

I wouldn't run off that left tank until you pull it and make sure what is in there.

 

[Boone83K10]

Its not very hard to drain yourself. Get a hand pump siphon from auto store. Look under truck and you can.see.the filler neck. Remove from the tank. Stick the siphon tube in it, drain into buckets. You will kno instantly if you have bad gas. After draining, you can remove 8 bolts on the frame and the tank will drop down. Remove fuel lines and sender line. Use screw driver and hammer to remove lock ring. Look inside tank and marvel at the rust or lack of it.