Difference is the detergent-dispersant package.
Ashless is tailored to engines that would run at steady load and throttle settings, boats trolling or wide open back to the launch or throttled to just be up on plane etc.
Low ash is tailored to engines that use varied loads and throttle settings. Motorcycles, chain saws, snowmobiles etc. Since many of these engines are aircooled low ash oils are often refered to as aircooled oil. The cooling mechanism really doesn't mean anything though, a watercooled varied load engine would use this oil too.
Both oils would provide plenty of lubrication and protection in either application, so your not going to ruin your engine using the wrong stuff, it may just run with bit more deposits using the correct detregent package. The main reason the outboard market evolved to an ashelss oil is the metallic ash could tend to build up on the plug gap (fouling the plug) and ring lands. On an engine with varied loads and throttle cycles the ash blows clear.
VOA's of oils show that many are now using both types of detergent formulation in the same product, so the difference may not be so clear as it used to be.
Originally Posted By: benjamming
Actually the manual says to use 89 octane rating minimum.
It also says "Do not use BIA or TCW rated (two-stroke water cooled) mix oils or other mix oils that state they are for use in both water cooled and air cooled engines (e.g., outboard motors, snowmobiles, chainsaws, mopeds, etc.)."
But why not?
