Trucks & Trailers - Stupid Question: Lower unit gear lube same as 80W-90?

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05-01-2011, 04:22 PM

I have several bottles of lower unit gear lube left over from an older Merc engine that I no longer own. I'm wondering just what the differences between this stuff and regular 80W-90 gear oil is. The lables state that it "For use in all outboard and sterndrive gear units specifying SAE 90, 80W90 or 85W-90, including OEM Type "C"."

I do have an older Chevy truck that uses 80W-90 in both the rear and front differentials (no posi) and I would like to use the lower unit lube in these if it is compatible. I imagine that the marine variant has more corrosion inhibitors than straight 80W-90, but other than that, are there other differences?


05-01-2011, 04:29 PM
You can use that stuff in the trcuk with no problem. it is the same stuff

05-02-2011, 02:43 PM
Same basic oil, just better additives. Lower unit oil has water resistant additives that help the oil adhere to the gears when slight amount of water gets introduced whereas standard gear oil does not have these additives. That's pretty much teh only difference between them. You'll notice how teh lower unit oil is almost impossible to wipe off your hands where as gear oil comes off with just a little wiping.

Roll Tide
05-08-2011, 07:33 PM
The marine oil additives also limit the amount of foaming in the oil. Since the lower unit is sealed any foaming could blow out a seal. Auto differentials are vented so foaming wouldn't be much of a problem.

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