Service Marine Lower Units to Prevent Water Damage

Preventing rust and other water-related problems in marine lower units.

Most other Marine Gear Oils fail to make the grade. We learn more on that from our own customers when they make the switch.

_by David Hilgendorf April 24, 2023

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.

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 – you can decrease the effects

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 is AMSOIL’s purpose built Marine Gear Lube

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.

WOW!!!

So next time you are about to place your expensive outdoor boat guy sunglasses up on the bill of your ball cap ask yourself if you checked and replaced you lower gear unit’s oil this year!!

Good Day

When to change differential fluids

John Baker|Nov 08, 2017 10:09 AM

It depends on your vehicle, driving conditions and differential fluid quality.

That’s a pretty vague answer, but it’s true.

If you drive your truck primarily on the highway in temperate conditions and rarely tow or haul, you likely don’t need to change front or rear differential fluid very often. But, if you tow a work trailer or haul supplies frequently and the temperature fluctuates as wildly as your health insurance premium, then you need to change the fluid more often. The only way to know the exact mileage interval is to check your owner’s manual or visit the dealership.

Bigger, faster, stronger

Why the varying fluid change intervals? Because severe operating conditions break down differential fluid more quickly and place greater stress on the gears and bearings, inviting wear.

The truck manufacturer’s ongoing arms race for the highest towing capacity has resulted in trucks that place far more stress on differentials than their predecessors. Meanwhile, differential fluid capacities have largely decreased or remained the same.

For example, compare a 1996 Ford F-250 Crew Cab to the 2017 version. Back in 1996, maximum towing capacity was 10,500 lbs. using a rear differential that held 3.75 quarts of gear lube. The 2017 model offers a 15,000-lb. towing capacity using a rear differential that holds 3.5 quarts of fluid.

Greater towing capacity, less gear lube

What does that mean for your truck? It means less fluid is responsible for guarding against increased heat and stress. In this environment, inferior lubricants can shear and permanently lose viscosity. Once sheared, the fluid film weakens, ruptures and allows metal-to-metal contact, eventually causing gear and bearing failure.
And in Sioux Falls looking out over 12th St every day, I see a lot of people overloading their light duty pickups!

Increased temperatures are also a challenge. As temperatures climb, gear lubricants tend to lose viscosity, while extreme loads and pressures can break the lubricant film, causing increased metal-to-metal contact and heat. The increased friction and heat, in turn, cause the lubricant to lose further viscosity, which further increases friction and heat. Friction and heat continue to spiral upward, creating a vicious cycle known as thermal runaway that eventually leads to greatly increased wear and irreparable equipment damage.

That’s why you need to change differential fluid more often in severe operating conditions.

In our example above, Ford recommends changing differential fluid every 150,000 miles in normal service. But they drop the change interval significantly – to every 30,000 miles if using non-synthetic fluid – when towing frequently at wide-open throttle and driving at temps above 70ºF. Those restrictions apply to just about anyone who’s pulled a camper/boat/trailer anywhere in North America during most of the year.

Bottom line…

Use a high-quality synthetic gear lube to maximize your truck’s ability to tow and haul.

AMSOIL Severe Gear 75W-110 ® Synthetic Gear Lube, Severe Gear 75W-90 (Best seller) and Severe Gear 75W-140 are specifically designed for severe service. It maintains viscosity better than other conventional and synthetic gear lubes despite rigorous use and it contains advanced anti-wear additives for further protection. It also costs less than most OEM-branded gear lubes.

FIND AMSOIL SYNTHETIC GEAR LUBE FOR MY TRUCK

Stay safe out there and visit our Sioux Falls AMSOIL Store at 4610 W. 12th St. (Just west of I29 about 1-block) 605-274-2580

Tag: 75W-90