Water and gear lube don’t mix. Unfortunately, you can’t avoid submerging your marine motor’s lower unit, and your boat isn’t going anywhere without the lower unit’s combination of gears, bearings and other components that turn horsepower into movement.
Video transcript: Service Marine Lower Units to Prevent Water Damage
Featuring John Gardner, ASE Master Certified technician, automotive technology instructor and host of Motorhead Garage, with AMSOIL Director of Product Marketing Len Groom (author profile).
John Gardner: I got a good idea. Take this boat motor. It’s sixty horsepower. You know, they have three hundred, four hundred, up to six hundred horsepower motors now.
Let’s take that power through a drive shaft, turn it ninety degrees through a prop shaft, and spin this propeller at a sick RPM. Better yet, let’s submerge it in some water. Not such a great idea, and you better have some good protection. Matter of fact, let’s look at the lower unit right there.
You can actually see inside of it, the exploded view. You got the drive shaft coming down. It’s connected to the actual propeller shaft I was talking about. But in between there are all kinds of bearings, gears to get the job done, and seals.
So you need lubricate it. AMSOIL has us covered. How do you lubricate it? Well, it’s pretty simple.
What you do is you just go through there. We went ahead and did ours. We removed the top plugs on there, and then we removed the bottom plug. What that did is it allowed it to drain.
We didn’t create a vacuum. Once we got that done, we replaced one of the top plugs. We went ahead and started filling the bottom till it actually overflowed. Then we put the top plugs in, and man, we were good to go.
But, Len’s back with AMSOIL. Len, man, there’s a lot going on in a lower unit. And put it in some water, you better have some good protection.
Len Groom: Yeah. It’s it’s a recipe for disaster is what it could be, especially with some of the fishing line that’s out there today. People throw it in the water, you end up running over it. It gets stuck in that output shaft seal and you’ve got problems.
You you fill it with water and the oil needs to provide protection no matter what. That’s the key with these. As you said, it there could be water ingestion. So you get water in it.
The AMSOIL Marine GearLube will still provide protection with up to fifteen percent water in it.
John Gardner: Now you’re out there fishing, you pick up some of that braided line, you don’t know it. You know, it was actually submerged in water. Water will get in there and you won’t know it till later till you see it dripping on the driveway.
Len Groom: That’s correct. And and there’s nothing you’re going to do about it. You just need to know that you’re protected. So we know that. We figure that into the formulation, and then we provide protection for you.
John Gardner: Now another game changer, Len, actually filling it up and doing it with the easy pack.
Tell us about that process and you have a pump as well.
Len Groom: Yeah. That’s correct. The easy pack is very simple. You just simply cut that end off and it will actually thread into that lower unit. So you just turn it a few times, it’ll bite, go ahead and squeeze it, roll it, whatever you have to do, and it’ll take care of you. And then for those that like to use the gear pump, we do offer it in a hard cork as well.
John Gardner: Make sure you follow your specifications and everything in your service manual when you’re doing a lower end service. But with AMSOIL, you’re not gonna have any problem. The easy pack and if you have any toy or outdoor equipment, just go to AMSOIL.com. They got you covered.
Lower units are resilient and can last for years, provided you service them annually. However, water can breach the seals and contaminate the gear lube in the lower unit, causing various problems.
Water contamination
Water contamination is bad for several reasons:
Viscosity loss – Viscosity measures a liquid’s resistance to flow or thickness. Your marine motor’s lower unit is designed to use a gear lube of a specific viscosity for optimal wear protection. Water can reduce the gear lube’s viscosity below what the manufacturer recommends, reducing wear protection.
Foam – A film of gear lube forms on the gear teeth it protects. This fluid film absorbs pressure and prevents metal-to-metal contact. Water contamination, however, invites the formation of foam. As the foam bubbles travel between gear teeth, they rupture under the intense pressure leaving nothing behind to prevent metal-to-metal contact, which leads to premature wear and potential gear damage.
Sludge – Water produces sludge, inhibiting heat transfer and increasing the lubricant temperature, which speeds chemical breakdown. The faster the lubricant breaks down, the sooner it fails to provide adequate protection, and the sooner it must be changed.
Rust formation – Water contamination invites rust formation on metal surfaces. Rust can flake off and circulate throughout the gear lube, where it acts like sandpaper and scours bearing and gear surfaces.
The solution
Avoiding contact with water is impossible when boating, so we’ve engineered AMSOIL Synthetic Marine Gear Lube to deliver advanced protection against power loss and gear wear, even with up to 15% water contamination.
This article is part of our Marine Engine Maintenance guide. See every article in the guide.
Recommended AMSOIL products
Start with AMSOIL Synthetic Marine Oil and find the exact AMSOIL products for all your vehicles with the AMSOIL Product Guide.
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David Hilgendorf is an AMSOIL Technical Writer who develops content for automotive, powersports and industrial audiences. His work includes technical data sheets, magazine articles, blog posts, white papers, product literature and application guidance. Hilgendorf works with engineers, laboratory personnel and technical specialists to communicate lubricant testing, product performance, maintenance practices, metalworking fluids, grease, motorcycles, marine equipment and industrial reliability.
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