Topic: Interesting find and a bit of Corvette history
in Forum: C3 Fuel, Emission Control, and Exhaust Systems


"The case history of the Chevrolet Corvette is particularly instructive. In 1975 the Chevrolet Corvette was unable to meet FMVSS 301 and not leak more than one ounce of gasoline a minute after a 30 mile per hour rear end moving barrier crash. GM's solution was to introduce a rubber bladder which provided the necessary protection against gas spillage inasmuch as the tank is located in the crush zone approximately 8 inches from the rear bumper. The history of bladders in competition race cars and in aircraft has been well documented with a variety of problems: deterioration, condensation, folding, cracking and the like. General Motors in 1978 introduced one of the safest gas tanks in the U.S. in its Corvette line by replacing the problematic rubber bladder with a High Density Poly-Ethylene ["HDPE"] liner.
HDPE is a common material for gas tanks today and an overwhelming number of safely positioned tanks on the road today are made of this plastic. It is capable of taking heavy blows and is slow to burn. It has proven itself as an automotive construction material in a number of applications.
Because the gas tank on the Corvette is directly in the crush zone for a rear impact, General Motors engineers encapsulated the HDPE tank within a standard metal tank and created a double-walled tank that has performed extremely well since 1978.
Based on the absence of fire claims from rear-end collisions suffered by Corvettes, and the vehicle's ability to be repeatedly certified by General Motors in compliance with FMVSS 301 for every production year since 1978, there is good reason to believe that a similar style HDPE/metal tank would enhance fuel system integrity of GM pickups with side saddle tanks.
General Motors's internal crash testing records indicate that an HDPE liner within a metal tank can provide a substantially higher level of protection than now exists.
On January 19, 1982, General Motors Safety Research & Development Laboratory Engineering Staff conducted a vehicle to vehicle left side impact crash test at GM's Proving Ground. The bullet vehicle was a Chevrolet Citation that was impelled directly into the left side of a 1982 Chevrolet K20 Pickup at an angle of 90 degrees and at a speed of 81.5 kph, or roughly 49 mph into the midpoint of the wheelbase, i.e. at the location of the gas tank. The pickup had been modified with a "20 gallon tank with plastic liner similar to [sic] 1982 Corvette." In the test this tank held 18.7 gallons. See GM Crash Testing Report C-5417. In this car-to-car crash test the rear tank strap separated on impact and the filler neck hose connection pulled apart at the connection to the fuel tank allowing the contents of the tank to be lost. In the slow motion film of this crash the tank itself withstood observable destruction.
On February 16, 1982, a similar crash test was conducted. See GM Crash Testing Report No. C-5434 which is incorporated by reference as though fully set forth. In this test a 1982 Chevrolet pickup was similarly struck at its left midpoint by a 1981 Chevrolet Citation at a speed of 85.9 kph or approximately 51 mph. This vehicle's gas tank was also modified with an interior Corvette style plastic liner. In the crash, only 44 grams of fuel leaked during impact from the fuel filler cap. The fuel tank spillage occurred due to an inadequate seal between the fuel filler neck and the fuel tank liner, but the fuel tank liner remained intact.
On May 27, 1982 GM engineers conducted a crash reported in See GM Crash Testing Report No.C-5496. Again a modified 1983 Chevrolet pickup with a Corvette style HDPE plastic tank liner was struck in a 90 degree side impact collision at 77.5 kph or approximately 47 miles per hour by a 1982 Chevrolet Citation. The impact produced extremely minor leakage, well within FMVSS allowable loss, in the total of 2 grams of fuel during the impact sequence itself due to a bolt at the front of the truck bed contacting the fuel line near the sending unit. The gas tank with plastic liner performed extremely well.
This crash testing when combined with the safety history of the Corvette crush zone fuel tank is a substantial foundation upon which to begin the independent safety testing and research of a retro-fit that will enhance the safety of these pickups.
Gas tanks lined with HDPE could be readily installed in the existing vehicle without modification of the gas tank compartment. A modified steel tank with a HDPE liner would fit into exactly the same space as the current tank. A modified sending unit that would attach directly to the new plastic/metal orifice would be necessary, but existing filler necks could be used to attach to the new safety tank. Existing hardware brackets would not need to be modified, although tank flat straps which have been roundly criticized as causing knife-like cuts into the metal tank should be replaced with wider, curved straps that use the existing brackets. "
Apparently, the bladder only survived a couple of years before GM found a way around it from other articles I read, but if you have one, your C3 has an excellent fuel tank!
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Brian - NCM Lifetime Member
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LukesVette Homepage
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Thanks Paul, very interesting reading.
Lifetime Member #116
Dave's '82

LukesVette Homepage
Veteran of Operation Iraqi Freedom
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