Re: unleaded additive???
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.<br /><br />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.<br /><br />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.<br /><br />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.<br /><br />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.<br /><br />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.
