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I am the happy owner of a '72 Corvette convert. I've got a long trip coming up and am verifying fuel economy and tank volume. I've had the car for a month now. Replaced the 190 deg. thermostat with a 180 and
tossed the clogged air filter for a new one. Then yesterday on fill up discovered that at fillup and being about one inch below the filler, it only held 12 gal, and this was a fillup with one inch of gas in the tank. Question is; do the convertibles have smaller tanks due to the top taking up space in the "trunk" when folded down? Its a 350 cu in with a 4 speed.
Hi gh,
I believe you'll find that the original gas tank for you 72 car held/holds 20 gallons (from the Quanta site).
The same tank was used for both coupes and convertibles.
Regards,
Alan
Perhaps you might want to get a look at it from under the car to see if you can spot a problem... perhaps the tank has 'collapsed' for some reason?
Because of the way the filler neck extends down into the tank about 1-1/4" it typically takes about 18 gallons to fill.
The fuel tanks that are designed to fit your year model are basically the same for convertible to a coupe in regards to the volume of them.
I think the volume is about 15 gallons. But I do not think that it will hold that much.
I would be careful IF you are topping off your gas tank and you have a vapor line running along side your brake line on the drivers side frame rail. filling up the gas tank that much can allow raw fuel to be sucked into this vapor line...which can...in time create other problems.
The only reason I write this is because I have to fix Corvettes with plugged up and split vapor lines on them.
Interesting question. I accidentally ran my 69 roadster out of gas (thought the gas gauge was broken.) upon closer inspection the sock was on the bottom of the tank. I was only able to get about 15 gallons back in it. Got it pretty close to the top. Gas gauge only showed about 3/4 tank. So I guess that's right if the sender is calibrated for 20.just don't see how it could possibly have taken another 5 gal.
The tank is "rated" at 18 gallons.
It has no bladder or liner as proposed above.
The filler neck sticks down into the tank and prevents you from completly filling it to it's @20 gal capacity for safety reasons.
You can try to bypass this by bumping the car to burp the tank but you'll find that the fuel splash back on your paint is not worth it.
I routinely fill my tanks when the needle gets to E and am rarely able to put in more than 15.5 gallons. There's always an inch or two of fuel at the bottom. Better safe than walking. So, while it may hold 18 gallons you'll likely find that there are realistically only 16 useful gallons on your trip as the last 2 gallons gives you less than 20 miles to find a gas station.
Last edited by Hammerhead Fred; Apr 29, 2018 at 06:27 PM.
I put a brand new sensor in a brand new 77 Quanta tank (no bladder). I fill my 77 up, and start driving, and its not long before the needle comes down from PAST F. Continue driving and its down to empty, go to a gas station and put 12-14 gallons in a tank that is advertised in the manual at 17 gallons. Honestly don't know how long I could drive past when it gets to empty.
But,....my 2015 Ford F150 is no different. All the technology, and they can't make a gage accurate. I can tell you in aircraft, gages are very accurate. Must be part of design standard for cars???
Of course, there is not a gage in my Corvette that is accurate, except maybe my speedometer (close) based on comparing it to a GPS speed.
Pictures below are from the original 77 Owners Manual...so it appears APPROXIMATE is the word. The used every way to write it that makes sure nobody holds the fuel quantity system to being accurate!
Last edited by Shovels and Vettes; Apr 29, 2018 at 05:48 PM.
Also, as Alan stated, the filler necks on later C3's, like all cars since then, has a filler neck down from TOP of tank, which prevents anyone for truly filling up the tank to the top....always leaving a space for expansion, for one thing. Maybe that is partial explanation why you can never put as much gas in the tank as the manual says is the capacity.
In a 77, the fuel vent system is mounted in the very TOP of the tank, so you cannot force fuel into the vent system. I don't know about what might "slosh" into the vent system while driving.
Last edited by Shovels and Vettes; Apr 29, 2018 at 06:04 PM.
Thanks for all the replies. Preliminary checks show I'm getting @ 12 mpg. As I've only had the car a month I'm slowly working my around to eliminate items that can contribute to poor gas mileage. It came with
a 160 deg thermostat which I changed to a 180 and replaced the dirty air filter. Fuel pump pressure is @ 7lbs and I hear no pinging, even on 87 octane, which the previous owner said it was ok to use. The Rochester carb looks pretty unmolested and I've been giving some thought to an aftermarket Holley EFI. Any thoughts on the conversion?
Thanks for all the replies. Preliminary checks show I'm getting @ 12 mpg. As I've only had the car a month I'm slowly working my around to eliminate items that can contribute to poor gas mileage. It came with
a 160 deg thermostat which I changed to a 180 and replaced the dirty air filter. Fuel pump pressure is @ 7lbs and I hear no pinging, even on 87 octane, which the previous owner said it was ok to use. The Rochester carb looks pretty unmolested and I've been giving some thought to an aftermarket Holley EFI. Any thoughts on the conversion?
My 72 350 A/T got 14 around town and 15 on the highway.
2020 Corvette of the Year Finalist (performance mods)
2019 C3 of Year Winner (performance mods)
2016 C3 of Year Finalist
my old motor was out of a 72 LT1 and when the 4 bbl wasnt fully openning I got above 16mpg. Once I fixed/adjusted the bent pedal arm it went down but was more exciting to drive. I've never gotten more than 14 gallons in my tank, most of the time its a 12 or 13 gallon purchase. I have a 68 with no liner in the tank
Thanks for all the replies. Preliminary checks show I'm getting @ 12 mpg. As I've only had the car a month I'm slowly working my around to eliminate items that can contribute to poor gas mileage. It came with
a 160 deg thermostat which I changed to a 180 and replaced the dirty air filter. Fuel pump pressure is @ 7lbs and I hear no pinging, even on 87 octane, which the previous owner said it was ok to use. The Rochester carb looks pretty unmolested and I've been giving some thought to an aftermarket Holley EFI. Any thoughts on the conversion?
its a great upgrade ,,,but for good fuel economy and performance I would look into a overdrive tranny.get the rpm down and you will have better mpg.
fuel tank volume
