Full synthetic marine gear lubricant?

[Charlie T]

Originally Posted by Loub52

The gear oil was recommended as a suitable alternative by a hardware clerk. They had no fully synthetic 5/30 engine oil available. The more I thought about the suggestion as I was about to break the seal on the container and finish changing the oil, I thought it would be better to do some more checking.

Let me start by saying I'm a huge proponent of Synthetic oil, I use it in all my engines. BUT, don't blindly substitute Synthetic for Dyno oil in small engines or older engines without full knowledge of what you are doing.

Virtually all modern Auto engines use a Roller lifter on the camshaft, this type of lifter reduces internal friction and allows for more aggressive valve lift events which can equal more power, better emissions and better mileage. Older engines and most small engines like a snowblower have an old style "Flat Tappet" cam/lifter. The flat tappet engines require a zinc additive known as ZDDP to combat excessive wear between the lifters and cam. As modern engines, with roller lifters don't suffer from this wear issue, most, not all synthetic oils don't have the ZDDP additive. Use of this type of oil without ZDDP in a flat tappet engine could result in excessive valve train wear and engine failure. There are some synthetics that specifically include the ZDDP needed, I know of a few specific Mobil 1 formulations that have it. The V twin oil designed for Harley's is one of them. Use caution when straying on oil types in an engine, it's easy to do more harm than good.

YMMV of course.

Charlie T