nelson007

I went to fill up my 1970 LT-1 I had about a ¼ tank. I drove about 25 miles to the gas station, and it is hot here today. When I started to remove the gas it exploded, it was like opening a bottle of champagne. I had replaced the cap with sealed gas cap when I broke the key off my locked cap. If the sealed cap is correct part to use what could be my problem.
Thanks in advance,
Nelson007

mrvette

Without posting a seriously long post, always have a vented cap....

circumstances make that a reality....

you can have that float/vent trick on the left/driver's side of the car, up top there, BUT when the tank is full and warming up the vent pulling up through the suction line from the charcoal canister will keep the little plug/float valve up top and so the pressures will built up on a long road trip....BTDT.....

get a vented cap...fought that crap for some years in my garage with vented fumes due to a NON vented cap....pressure build up and such...

KRAZY, I know.....


pressure/fumes gotta go somewhere, better on the roads so as not vent out in your garage....

nelson007

Your correct. I will use the one from my 68 until I pick up one at Carlisle.
Thanks,
Nelson007

7T1vette

Every (non-pressurized) fuel tank needs a vent. That can be mounted on the tank, in the fuel cap, or via some device connected to the tank [like a fuel vapor canister]. But, I think you found out why that is truly a requirement.

Alan 71

Hi Nelson,
I'm curious what you mean when you say 'exploded'?
You should hear a 'whoosh' as the pressure is released, but certainly not a 'bang'.
70-72 gas tanks used a 'sealed' gas cap. People were surprised by the 'whoosh' so a note was added to the 71 and 72 caps. "CAUTION Open Slowly". (The same caution that's on the radiator cap.)
The 70 to 72 tanks, (and perhaps others), have a pressure relief valve. It's about the size of quarter and located just to the left of gas filler neck. You can just see it in the upper right corner in this picture. I'm curious if your tank has it, and if it's working.
When I read 'exploded' I was afraid I'd see your car on the local news!!!!!
Regards,
Alan

nelson007

Hello Alan,
No, I did not get a ‘whoosh’. I got the sound similar to what I said earlier, a Champaign Bottle being opened. I only drove from Bachman Valley to South Hanover. When opening the cap it surprised me that I dropped the cap and the keys that were in my other hand. Is it possible the vent in the tank is clogged, or perhaps it is not correct tank? If I remove the rubber boot around the gas tank will I be able to see the vent cap? For now I will get the vented cap off my 68. The 68 is getting all new wiring and vacuum line put in.
By the way do you take your car to Carlisle?
Have a good Sunday,
Nelson 007

Alan 71

Hi Nelson,
You should really just hear a 'whoosh'.
Not to over think this, BUT; the original filler neck's flange has 3 'ramps' built into it so as you begin to turn the cap, the pressure is released gradually as you turn. You reach a point that the cap has turned far enough to be off the ramps, (and the pressure released), but you still can't lift it off. You must turn it about 1/8th turn further to be able to lift it off the neck.
I guess I'd check to make sure your filler neck has the ramps, and the cap you have makes use of them.
For a while the caps just had SEALED on them and this tag was added. Then the caps continued to be stamped SEALED and the stamped info OPEN SLOWLY CAUTION was added.
I do attend Carlisle, but haven't ever brought my car.
Regards,
Alan

7T1vette

If the car has a working vapor recovery canister system, I don't think you should even get the "whoosh" when you open the cap. The cap is sealed....but the system is not. If you get a significan whoosh of trapped air from the tank when you remove the cap, I suspect a problem with the vapor recovery system.

Mike Ward

Spot on.

Dave J

I see by your recent posts you are a new C3 owner. If your LT-1 is in original condition, it should have a gas tank with the relief valve as Alan posted, and only one gas line from the tank to the fuel pump. There should be no fuel return line on an original LT-1.

If this is a recent restoration, one could suspect a non correct gas tank has been installed, with no relief valve. Try to verify the gas tank you have is the proper one.

I have 2 very original '70 L46 cars, with the original gas tanks, and both have the SEALED logo gas cap. When I put gas in, I do feel and hear a slight "whoosh" from the filler neck, but never a problem. The only difference is my gas tanks have the second vapor return line.

nelson007

Thanks for all the help. I was haveing problems getting the cap off. I might twisted too fast and too hard. I am going to check to see if the ramps might be bent.
Thanks
Nelson

Alan 71

Hi,
I still believe the tank is pressurized under operating conditions.
If it's not, why the 'Caution' on the gas cap, and why the purge valve in the vapor canister?
Regards,
Alan

nelson007

Thanks Dave,
I am new with the C3’s. I now have a 68 427/435 and this original 70 LT-1. We will be taking the body off in the fall for a complete restoration. There is only one gas line from the tank to up front. I won’t be able to verify the tank until I get the body off. The car has never been restored. The engine was rebuilt 3000 miles ago and that was 6 years ago. For now I guess I will have to use a vented cap. Do you think I should try using the sealed cap and see what happens? Can it do any damage to the car.
Thanks,
Nelson007

jim2527

So help me out here...

'70's don't have emmisions equiptment...no vapor recovery charcoal tanks. Without the emmisions systems how are tanks supposed to be vented?

7T1vette

Reread post #4...

jim2527

Post #5 says '70's are supposed to have 'sealed' caps, if that's the case how are '70 tanks vented?

7T1vette

If sealed cap and no recovery system, it must have a vent on the tank.

Easy Mike

That's about the time I would have had to go back home to change my pants.

7T1vette

Something is definitely not right with that tank system.

Alan 71

Hi,
I believe a 70 LT-! without ECS, (ECS was on cars delivered to California), have the 'button' relief valve that all sealed tanks had.
Regards,
Alan,