LT-1 gas tank configuration

[Roger O.]

Re: LT-1 gas tank configuration

Joe,
Didn't think about that but then I'm not following you on why the vent on top of the tank would be better than the vent in the cap ? It would seem the vapors from the cap vent would escape around the lid and be gone quickly but the tank vent would be prone to being trapped under the body thereby lingering.
I've found in the past a very tiny fuel leak at one of the nipples on the top of the tank can almost run you out of the car from the smell.

[Joe L.]

Re: LT-1 gas tank configuration

Joe,
Didn't think about that but then I'm not following you on why the vent on top of the tank would be better than the vent in the cap ? It would seem the vapors from the cap vent would escape around the lid and be gone quickly but the tank vent would be prone to being trapped under the body thereby lingering.
I've found in the past a very tiny fuel leak at one of the nipples on the top of the tank can almost run you out of the car from the smell.

Roger------

I believe the configuration of the rear deck on 68-73 Corvettes causes the vapors vented from the fuel cap to be carried back into the passenger compartment.

For the most part, the area on top of and surrounding the tank is sealed off from the passenger compartment and vapors are carried away under the car from the passenger compartment. This does not, of course, apply to an actual fuel LEAK like you described since a fuel LEAK will almost always by noted in the passenger compartment regardless of where it is on the car.

I can tell you this: from the time my 1969 convertible was new I would at times note the odor of gasoline in the passenger compartment. It wasn't bad enough to complain about and, in those days, the odor of fuel was so common it was pretty much "accepted". My car was a hard-top only and I rarely took the hard top off. It was when the hard top was off that the odor of gasoline was most prevalent (this was obviously mostly in the summer months which exacerbated the vapor problem).

In 1986 I put a soft top on the car and the problem increased. Plus, I had the top down a lot more.

My car is a late 1969 and had the integral pressure/vacuum valve and also the vented cap. I discovered the pressure/vacuum valve was actually leaking gas, although I don't think it had been since the car was new. I think it had failed progressively over the years. So, I removed the valve and sealed it, figuring I now had, effectively, the same configuration as earlier 69's. The fuel odor problem was greatly reduced, but it was still there to about the extent I had experienced since the car was new.

At this point, I decided it was time to replace the tank (even though it had absolutely no evidence of ANY internal or external corrosion). I replaced the tank with a new GM tank (it even still had the O.L. Anderson logo at that time) with pressure/vacuum valve, identical to my original tank.

I still noted the odor of fuel in the passenger compartment under certain conditions. So, I replaced the fuel cap with a sealed cap of GM #3994339, as GM instructed. Problem was over---completely and permanently.

[Roger O.]

Re: LT-1 gas tank configuration

I still noted the odor of fuel in the passenger compartment under certain conditions. So, I replaced the fuel cap with a sealed cap of GM #3994339, as GM instructed. Problem was over---completely and permanently.

Interesting. I guess coming this summer I'm going to have to do some sniffing around some gas caps. I would have guessed there would have been more going "in" through the valve than coming "out" ( with the use of the fuel). I guess it might depend on how much fuel sloshing is going on also. Thank goodness for the charcoal canister addition. And thanks for the explanation Joe.

[Joe L.]

Re: LT-1 gas tank configuration

Interesting. I guess coming this summer I'm going to have to do some sniffing around some gas caps. I would have guessed there would have been more going "in" through the valve than coming "out" ( with the use of the fuel). I guess it might depend on how much fuel sloshing is going on also. Thank goodness for the charcoal canister addition. And thanks for the explanation Joe.

Roger-----


The charcoal cannister only controls fuel vapor emissions from the engine side of the car. It does not control fuel tank emissions (although condensed vapors from the cannister are returned to the fuel tank).

[Roger O.]

Re: LT-1 gas tank configuration

Roger-----


The charcoal cannister only controls fuel vapor emissions from the engine side of the car. It does not control fuel tank emissions (although condensed vapors from the cannister are returned to the fuel tank).

All these years I thought the canister was a dual purpose canister that caught vapors from the fuel tank and carburetor and then in some years purged those fumes through the carb.
How are the condensed vapors returned to the tank ?

[Joe L.]

Re: LT-1 gas tank configuration

All these years I thought the canister was a dual purpose canister that caught vapors from the fuel tank and carburetor and then in some years purged those fumes through the carb.
How are the condensed vapors returned to the tank ?

Roger-----


There is only a single line that runs from the canister to the fuel tank. As far as I know, this is a "one-way" system.

One other thing: as a result of the incorporation of the EEC system into 1970 with NA-9 as well as all later Corvettes, it may well be that the fuel tank will never experience "pressurization". In fact, I don't see how it could. So, a release of vapors as a result of activation of the pressure release portion of the pressure/vacuum valve should never occur unless there is a failure of other components.

[Jack H.]

Re: LT-1 gas tank configuration

One explanation is if the tank is internally vented then there's NO DANGER of Bubba installing the wrong style gas cap resulting in problem(s)....

The issue of vented tank vs. vented cap goes WAY back. If memory serves, Corvette began life with vented caps and sealed tanks then switched to a vented tank with sealed cap in 1957. So, this isn't just a C2/C3 issue.

[Roger O.]

Re: LT-1 gas tank configuration

Does anyone have the specs for the valve in the tank ?
Does the valve in the cap have the same specs ?
How much pressure can build inside the tank before it releases ?
How much vacuum can build before it releases ?

[Joe L.]

Re: LT-1 gas tank configuration

Does anyone have the specs for the valve in the tank ?
Does the valve in the cap have the same specs ?
How much pressure can build inside the tank before it releases ?
How much vacuum can build before it releases ?

Roger------


My humble apologies to you and all. I was leading you all down the wrong path and I was just about 100% incorrect on this and it HIGHLY embarrasses me. The evaporative emission control system does draw gasoline vapors from the tank and not the other way around. So, the vapor return line is one way, but it's one way from the tank to the canister.

Notwithstanding the above, the fuel tank does incorporate a pressure vacuum valve. Presumably, this is set to relieve at a higher pressure or vacuum than the EEC system operates under.

As far as the pressure and vacuum relief settings of the fuel caps and the integral pressure vacuum valves, I don't know what they are. I've been trying to find data on this for years. Some time ago I figured I'd need to determine it experimentally. To do so, I'd need to set up "adapters" for the tank and caps. I've never gotten around to it, though. Someday, maybe.

[Mike E.]

Re: LT-1 gas tank configuration

Joe--
It takes a big man to say "I was wrong". Thanks for your honesty.
I am assuming that the conclusion remains correct that there is only 1 nipple on the tank for 71-72 LT-1's and that is on the left (driver's ) side.
Regards,
Mike

[Roger O.]

Re: LT-1 gas tank configuration

Joe--
It takes a big man to say "I was wrong". Thanks for your honesty.
I am assuming that the conclusion remains correct that there is only 1 nipple on the tank for 71-72 LT-1's and that is on the left (driver's ) side.
Regards,
Mike

I agree 100%. Thanks Joe !!!
( I was getting scared I was going into the first stages of oldtimers. LOL)

Mike here is a link to Quanta. If you go to page 2 there are 2 listed tanks for the LT1 (#33F and 33G). It tells details about the nipples and tank venting. I wont swear this is 100% accurate but I do believe its close. If you choose a Quanta tank with "valve in top of tank" make sure the valve works before driving your car very far. I've had 2 and have heard of others that the vent failed and the tank sucked down and caved in.

http://www.quantaproducts.com/products.asp?dept=19&pagenumber=1&sort_on=&sort_by=

[Mike G.]

Re: LT-1 gas tank configuration

no. nothing on the drivers side of the tank. lt1 tank is the only one like this. you still use the same sealed gas cap as the others. the vents are soldiered in to the top of the tank.

[Joe L.]

Re: LT-1 gas tank configuration

Joe--
It takes a big man to say "I was wrong". Thanks for your honesty.
I am assuming that the conclusion remains correct that there is only 1 nipple on the tank for 71-72 LT-1's and that is on the left (driver's ) side.
Regards,
Mike

Mike------


Yes, that's correct (for sure, on this).

[Joe L.]

Re: LT-1 gas tank configuration

no. nothing on the drivers side of the tank. lt1 tank is the only one like this. you still use the same sealed gas cap as the others. the vents are soldiered in to the top of the tank.

Mike-----


The LT-1 tank has no nipple on the UPPER RIGHT (PASSENGER) side of the tank. This is because there is no fuel return line (from the fuel pump) on an LT-1. However, for 1970 LT-1 WITH NA-9 and ALL 1971-72 LT-1, there is a nipple on the UPPER LEFT (DRIVER) side of the tank for the EEC system. There's also a bracket on the upper left for mounting of the fuel vapor separator for the EEC system.

I blew it on the EEC system functionality issue but I'm certain about this part of the configuration.

[Mike G.]

Re: LT-1 gas tank configuration

here is a pic of my original 70 lt1 tank and a pic of the replacement. without the rust you can see the vent in the pic. the original tank is junk but for some reason i cant part with it. you can also see what is left of the tank sticker. the non lt1 tank has a nipple in the indention on the drivers side top.