1953 - 1971 Corvette: Service Bulletin: Gasoline Additive for Preventing Exhaust Valve Recession

Subject: Gasoline Additive for Preventing Exhaust Valve Recession
Model and Year: Pre-1971 Passenger Cars and Trucks, 1971-1978 Trucks over 6,000 Lbs. GVW, 1979-1986 Trucks Over 8,000 Lbs. GVW
Source: Chevrolet Dealer Service Bulletin
Bulletin No: 86-260-0A
Section: 0A
Date: May, 1988

TO: ALL CHEVROLET DEALERS

Some engines designed to use leaded gasoline may experience exhaust valve recession if operated at high speeds and loads with unleaded gasoline. Therefore, if leaded-gasoline is not available, or if additional protection is desired with low-lead gasoline, the GM Anti-Valve-Recession Additive, Part Number 12345492, may be used. The recommended dosage is one container per tankful (20 gallons) of unleaded gasoline, which should provide valve protection equivalent to leaded gasoline with a lead concentration of 0.1 grams per gallon.

This additive can be used in all GM gasoline-fueled engines in:

pre-1971-passenger cars and trucks
1971-1978 trucks over 6,000 lbs. GVW
1979-1986 trucks over 8,000 lbs. GVW

NOTE: Additive should not be used in engines designed to operate exclusively on unleaded gasoline (with restriction in fuel tank filler neck).

As a reminder, the engines mentioned above were designed to use a fuel with a minimum octane rating of 89, (R+M)/2 (average of Research and Motor octane numbers). If unleaded fuel is used, be sure that it has an octane rating of at least 89 (R+M)/2.