Do I have an EEC gas tank?

[dzwestwindsor]

My gas cap has been leaking, so I'm going to get a new one. In the Classic Parts catalog they have a pressurized cap for EEC tanks and a vented cap for non EEC. How do I figure out which one I have? It's a 1971 C20 with a 350, tank should be stock. Were the 71s EEC equipped? Or where do I look to find out?

[snj8198]

The EEC "Evaporative Emmisions Controls" tanks had an extra vent. Look at the passenger side upper corner of the tank to see if yours is there. This vent and line will run up into the pillar behind the passenger door, loop back down through the floor, and follow along the right frame rail to the front corner of the engine compartment. At least mine did. From what i can tell mine was originally a California truck.

[dzwestwindsor]

It looks like mine doesn't have it. It only has that one hose and wire that goes in the top center. So I guess I need to buy a vented gas cap? Is it common for these vented caps to leak with a full tank, say when I make a sharp right turn, or park on a sideways incline? Cause my current one does that, but it's probably just too old.

[tinlid]

The 1st time my cap leaks on my 70 c10 I replace the cap. I have replaced 2 in the last 13 years. After a while the old cap just does not seal anymore.