1970 LT-1 Fuel Cap

[Joseph F.]

Can anyone tell me whether the fuel cap on a real 70 LT-1 should be vented or not.
I know all the parts books say that they are all non-vented.
But this tank does not have evaporative emissions. There is no vent line on the tank or a return line from the fuel pump back to the tank. The tank has no provisions for any vent hoses.
This is a correct set up for the 70 LT-1 only.
The reason I asked is I was adjusting the rear float level and the fuel started to pour out the site hole, so we shut the engine and the fuel still continued to flow. Once we removed the fuel cap the fuel stopped.
So the tank built up quite a bit of pressure and that is why I feel this car should have a vented cap.
Thanks, Joe

[Alan S.]

Re: 1970 LT-1 Fuel Cap

Hi Joe,
Doesn't the tank for the 70 LT1 still have the small, button relief valve thats just to the left of the filler neck? Could this be mal-functioning and causing the pressure build up.
Regards
Alan

PS: I'm looking at Quanta's 33G tank, which I believe is your application.

[Jim T.]

Re: 1970 LT-1 Fuel Cap

Terry M. has an original owner LT-1 and will be able to give you the correct answer.
My original owner 70 350/300 still has it original non-vented gas cap. Still has the original tank. Since new when the gas cap is removed there has been pressure heard from the tank. Don't know when the pressure relief valve is activated to release pressure. Do have a fuel return line on my 70, but no other emission lines from the tank going to a cannister.
Back in 1975, when NCRS did not include C3's, I put a non-vented GM locking gas cap on my 68. Wrong thing to do. I had already been using a non-vented GM locking gas cap on my 70 with no problems.

[Jack H.]

Re: 1970 LT-1 Fuel Cap

Keep in mind, 1970 was a Jeckyl & Hyde year where California jumped the gun and required their own emissions compliance. That said, roughly 10-15% of Corvettes shipped to/through California and they would have been equipped with the NA9 option which included the charcoal cannister vapor recovery system that became standard in 1971. So, it takes more than just saying this/that car is a '70 LT1 for specific answers about the gas tank, fuel & vapor lines....

[Terry M.]

Re: 1970 LT-1 Fuel Cap

To the best of my knowledge ALL 1970 Corvettes originally had a gas cap marked SEALED. If the cap functions properly, one can take that to mean exactly what it says. My 1970 LT1 (NO NA9) came with one -- and it still works fine.

Alan correctly describes the tank vent on 1970 Corvettes -- I believe ALL 1970 Corvettes had this vent/relief valve.

There was a discussion about this vent/relief valve a while back because someone had there new gas tank implode due to a malfunctioning valve. I believe that thread even contained a photo of the valve. Joe Lucia was kind enough to post in detail the different fuel tank and cap applications for the early C3s in that thread. I could not on my best day come close to duplicating Joe's wisdom.

[Alan S.]

Re: 1970 LT-1 Fuel Cap

Hi Joe, Again,
This picture shows the valve to the left of the filler neck. I have no GOOD excuse for the 'tank tone'!!!! At least I have the plastic 'shield'.
Regards,
Alan