Truck differential lube in outboard lower unit?

[Steve Foss]

So I'm wondering if the 80-90W gear lube I use in the differential for my pickup will work for the lower units of my outboards, which take 90W lube. Looks and smells like the same stuff to me.

I've got a gallon of 80-90W differential lube from when the differential gasket on my pickup leaked and figured I'd use it on the outboards instead of buying more lower unit lube, if it'll work OK.

Thoughts?

[Pat K]

I've always been told that the marine lube is a non foaming lube.

Because the lower unit is a small preasure sealed case, if you use regular lube it will foam during high speed use and blow out the seals.

True or not it's been enough to scare me into using only marine lube.

[marine_man]

You can use it steve (I'm sure lots of other poeple have in the past as well), but Pat K's understanding is the same as mine... gear lube for lower unit lube is specifically formulated for use in lower units to prevent foaming, tolerate water better, etc.

marine_man

[Steve Foss]

Thanks, guys. I'll just garage sale the gallon of gear lube and pick up more lower unit lube for the 90 Merc and 9.5 Johnson. If the truck lube foams and doesn't tolerate water as well as the other, well, why risk fried lower units in order to save $15? Already had a new stator, impeller and lower power pack put in on the 90 last fall, and the 9.5 (from 1969, it was my grandpa's) was totally rebuilt two years ago, so I'll go the safe route.