lower unit gear lube??

[kerryd15]

What is the difference between Marine gear lube and gear lube, both 80W90 and same rating? besides price and the size of the tube it comes in

I have an 97 Merc 50, any ideas how much this holds? thanks

[BobT]

I don't know this for a fact but I've always figured that because lower units operate under water there's a much greater chance of water contamination than say the rear-end of your car. With this in mind I suspect that marine grade gear oil is designed to maintain friction control even if contaminated to some degree with water.

[Northlander]

Use the marine stuff.

[Eric Wettschreck]

Your lower unit should hold a little shy of a quart.

Use the marine stuff.

There are additives in the marine lube to inhibit foaming. The crank output shaft spins at a much higher speed than a conventional pinion or ring gear in a rear end. This will cause the lower unit oil to foam if you use regular 80-90.

[boatfixer]

Stick with marine stuff. Anti-foaming and rust prohibitive as the others mentioned.

Your 50 will hold 12.5 oz's

[theoilman]

Marine gear lube is GL4 rated while automotive differential lube is GL5 rated. Do NOT use GL5 (especially petroleum) in a marine lower unit. The petroleum GL5 uses additives which will probably damage any yellow-metal bearings and/or thrust washers used in marine lower units. To be save always stick with a marine label even if it is more expensive. Most brands of marine labeled will have extra rust and corrosion protection as well as better anti-foaming than automotive rated products.

Additional info: AMSOIL Marine Gear Lube carries an additional rating I have never seen on any other - it will tolerate up to 10% water intrusion and not lose lubrication protection.

Recommended to always service your lower unit in the fall before storage - make sure to remove any possible water before danger of freezing!

[kerryd15]

Thanks for the replys. nothing open on sunday except wally world and was looking at their fluids. both marine and regular gear lube was GL5. That got me thinking of the question. Drained the motor over night and got roughly 8 oz out. thought maybe it wasn't full but that is all that fit. Bought some marine lube for merc and merc cruizers from the nada place.

Thanks