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Attached is a copy of a Chevron report generated after about 15 years of gathering data on "unleaded gasoline use in older vehicles".
Use of Unleaded Gasoline in Cars Designed for Leaded Gasoline
With all the media attention being given to the reduction of lead in gasoline and the potential of phasing out leaded gasoline, many consumers are asking the question "If my car was designed to run on leaded gasoline, will it operate satisfactorily on unleaded gasoline?"
The answer to the question is yes. The chief concern has been for the possibility of exhaust valve recession (sink or seat wear) when these engines are operated on unleaded gasoline. After 15 years of experience in marketing Chevron Unleaded Gasoline, we felt that enough accumulated data could be obtained from different sources to allow us to finally arrive at some definite answers.
Passenger Cars and Light-Duty Trucks: Based on an extensive survey of the published literature, fleet operators, engine rebuilders, and manufacturers, we conclude that all typical passenger car and light-duty truck engines (representing 94% of U.S. gasoline consumption) are safe from valve recession when operated on unleaded gasoline. They are either equipped with induction hardened valve seats or subjected to service too mild to cause problems. The problem can only occur in older engines when operating under sustained high speeds and loads.
Vintage Vehicles:
Antique cars are typically exposed to such light service that they are not expected to have any valve seat problems. In fact, they stand to benefit overall from a reduction in exhaust system corrosion and oil contamination.
Heavy-Duty Industrial Engines:
Specifically, these engines are moderate displacement engines, and some large displacement heavy-duty truck engine in industrial applications. Many of these were equipped with alloy valve seat inserts (alone or with stellite faced valves) which offer the best protection against valve seat wear. These engines account for about 6% of total U.S. gasoline consumption. Some heavy-duty gasoline engines without valve seat inserts might be vulnerable to damage in severe service. The exact number of these is unknown, but they clearly consume much less than the 6% of U.S. gasoline for this category. For those few engines without valve seat inserts, preventive measures should be taken to reduce the severity of their service. Avoidance of full throttle operation for extended periods is primarily what is necessary. As a last measure, install hardened inserts and/or stellite valves, if possible, or utilize a commercially available lead substitute additive in the fuel.
Marine Engines:
There is concern about older four-stroke cycle engines in marine service, which were designed prior to the introduction of unleaded gasoline (pre-1974). Under severe duty, these older engines could have valve recession problems. If these engines are in severe duty service, owners should consider installing hard seat inserts or using lead substitute additives to minimize valve recession. Products like this have been found effective in minimizing valve recession.
Mercury, who is a major supplier of Stern Drive Engines for marine use, advises that their engines are automotive based and have hardened exhaust valve seats. Most of Mercury's outboard engines were developed with unleaded gasolines, and Mercury's only concern is with octane number. All of Outboard Marine Corporation's current four-stroke cycle engines were designed for unleaded gasoline and valve protection additives are not needed. Additives are also not needed for their two-stroke cycle engines, however, some of them may have the need for octanes higher than 87(R+M)/2. The newer Volvo Pinta Stern-Drive four-stroke cycle engines are designed for use with unleaded gasoline. Some of the older engines are not. We would suggest owners contact their dealer for advice if they have an older engine in severe service. Yamaha outboard engines operate satisfactorily on unleaded gasoline. At least one model, a high performance Model 225, requires a minimum 89(R+M)/2 gasoline. Outboard Marine Corporation has issued a Service Letter for General Information #53, August 1985, subject: Gasoline Lead and Alcohol. This bulletin is very comprehensive on their position regarding unleaded gasoline use and has extensive guidelines relating to their minimum octane level desired. This should be available from Johnson and Evinrude dealers. Farm Equipment: A federal sponsored study of older gasoline-powered farm equipment showed some performed satisfactorily on unleaded gasoline, but most experience valve-seat wear, especially during the water pumping portion of the testing. As discussed previously, operating at light load, replacing the valve seats with hardened inserts, or using lead substitute additives can help solve the valve-recession problems in critical engines.
Two-stroke and four-stroke cycle engines (motorcycle, small utility, and other various recreational vehicle engines): In general, two-stroke cycle will operate without problems on unleaded gasoline. These engines do not have valves, and most will actually benefit from using unleaded gasoline because of reductions in spark plug and combustion chamber deposits. Lead is not required to provide lubrication for pistons or piston rings, as is sometimes claimed. Owner's manual recommendations should be followed, particularly for new engines under warranty. Owners of older engines should contact the manufacturer for guidance in choosing a proper octane fuel, or to obtain service information about ignition timing and low compression kits which may be required for unleaded/low lead fuels of lower octane. In discussion with Briggs and Stratton, a major manufacturer of small engines for lawnmowers, pumps, etc., they indicate that all post-1979 engines can use unleaded gasoline and that they do not anticipate any problems with pre-1979 engines for normal service. Where heavy-duty service is anticipated, they suggest a valve protector additive be used. All models of their industrial and commercial small engines can use unleaded regardless of age. We have also determined that the following makes can use unleaded gasoline regardless of age:
Continental Homelite Honda Onan Tecumseh Wisconsin
Lead Substitute Additives: Since the advent of drastically reduced levels of lead in leaded gasoline, numerous lead substitute additives have appeared on the market. These products are designed to provide a protective coating on valve seats and inhibit valve sink. Because the composition of these products varies considerably, the labels should be read carefully to ensure safe handling. These lead substitute additives are not needed and should not be used in two-stroke cycle engines.
Summarizing, we do not see problems occurring in the overwhelming majority of engines in all categories, when unleaded gasoline is used. Copyright © 1990 Chevron USA Inc. All rights reserved. ----- ----- ----- ----- ----- ----- ----- ----- ----- ----- ----- ----- ----- --
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