Lower unit gear oil

[harvey lee]

Is there a difference between regular gear oil and the stuff marked Marine use other than the name?

[kerryd15]

What I was told is yes. The marine oil is made to lubricate and not breakdown even if some water gets in it.

[Pat K]

I've always been told the marine lube is non-foaming to prevent excessive pressure in the lower unit.

[marine_man]

That's correct.. use the marine stuff.

marine_man

[JohnMickish]

The driving differential of a car/truck is vented to allow for the escape of air when it warms up, and to allow air to re-enter when it cools. We are not talking a large amount of air here, but enough to blow seals when the vent gets plugged.

A lower unit is not vented for obvious reasons, so it must use an oil that does not expand when heated.