A reader asks: I am looking for some input on outboard 2-stroke oil selection. Having reviewed all the product literature from AMSOIL, it seems that I have three choices, but I cannot determine which is best suited from my motor. My engine is a Mercury Outboard 90 hp, and my choices seem to be: (i) Synthetic 2-Stroke Injection Oil (AIO), (ii) HP Marine Synthetic 2-Stroke Oil (HPM) and (iii) Outboard 100:1 Pre-Mix Synthetic 2-Stroke Oil (ATO). I pre-mix my fuel at 50:1. The outboard is carbureted. The original oil spec recommended by Mercury was TC-W.
Our answer: There is not a wrong choice between those three products for your engine. Any one of these products would be a fantastic upgrade. But let’s narrow it down.
“HPM” HP Marine
AMSOIL HP Marine Synthetic 2-Stroke Oil (HPM) would be the ultra-premium choice. This sophisticated formula pulls out all the stops providing exceptional wear control and world-class deposit prevention. HP Marine also offers some quality features that are specific to marine applications. It has an anti-rust/corrosion package which provides engine protection both in and out of season. It also delivers very clean emissions and low aquatic toxicity. For engines that require premix, mix HP Marine at a 50:1 ratio.
“ATO” Outboard Synthetic 2-Stroke Pre-Mix Oil
Also very much a premium choice, “ATO” Outboard Synthetic 2-Stroke Pre-Mix Oil is AMSOIL’s dedicated oil for pre-mix only. This highly concentrated pre-mix oil that is designed to safely be mixed at ratios of 100:1. Outboard 2-Stroke Oil offers clean operation, low smoke/odor, low aquatic toxicity and optimum throttle response. Despite the proven 100:1 mix ratio, ATO Outboard makes absolutely no compromises in terms of wear control. It also contains a powerful anti-rust ingredient to keep engine internals pristine all year long.
“AIO” Synthetic 2-Stroke Injector Oil
AMSOIL Synthetic 2-Stroke Injector Oil (AIO) is a fantastic synthetic 2-stroke oil option with a moderate price tag. Despite being called an “injector oil”, it is designed for flawless operation when used as a premix at 50:1. AIO also delivers the features one expects from a good synthetic oil such as improved performance, excellent wear control and low smoke. Also quite suitable for snowmobiles, ice augers and two-stroke-powered yard tools.
To sum up, all of the mentioned products would work extremely well in your engine. The premium options would be HP Marine and ATO Outboard Synthetic 2-Stroke Pre-Mix Oil. A budget-priced alternative is AIO Synthetic 2-Stroke Injector Oil. AIO is still an upgrade over the vast majority of synthetic 2-stroke oils on the market. It really comes down to the price and a few nuanced differences in these products.
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