During a brief early summer swim in Mud Lake just East of the Little Sluice on the Rubicon Trail, I topped off my standard 10W-30 tranny fluid with lake water. It didn't look that deep -- I was only in up to the tops of my wheelwells... (33 inch tires, spring-over). At least I kept the air filter above the water lilies.

not me, and not as deep, but you get the general idea...

After I got home I did the standard deep-water drill -- drain and check all fluids, check chassis lube points, and repack the locking hubs. Everything looked good, and I was beginning to think UZI had emerged dripping but unscathed. The chocolate shake of emulsified oil and water that streamed out of the tranny and transfer case belied this hope.

Most Isuzu light trucks use a tranny and transfer case that essentially share the same oil bath. There are separate drain and fill plugs because a high point exists between the drain-plugged low points, but the oil intermingles. All told, I got more than two combined gallons of emulsified brown goo out of both drain plugs.

Water is easy to detect in quantity -- it emulsifies with the oil and makes the oil look cloudy instead of its yellowish clear natural state. Smaller quantities of water in the oil can still look nearly clear, but if you drop a few drips onto a hot manifold, water-contaminated oil sizzles as the water steams off.

After letting the gearboxes drain over night, I made some phone calls:

My local bearing manufacturer told me to just keep changing the oil, running the gearbox briefly at operating temperature, then changing the oil until I could no longer detect water in the oil. They said that this would either emulsify or evaporate the remaining water, and that one or two changes would do the trick.

 

Marlin, the maker of Marlin Crawler gears, suggested changing the oil, running the truck for 20 miles on the highway, changing, running, until the oil drained clear.

 

One of my cronies suggested that I wash out the inside with some type of alcohol -- since water would go into solution in the alcohol and just wash or evaporate away. I was too nervous about destroying seals to do this.

 

A chap from the off-road.list suggested I add a quart of Dexron ATF with the first few cycles of oil. ATF has many detergent addititves, but I wanted to stick to the manufacturer's recommendations for what I put into the gearbox.

I opted for a combination of the first choices, and did flush, fill, and run cycles until I was confident that I had no water in the oil. Two cases of oil was cheap insurance when compared to the cost of a tranny/transfer case rebuild or replacement.

Minute quantities of water will naturally work their way out when the transmission is at operating temperature. Tiny amounts of water can steam/evaporate off out the tranny vent. Larger amounts of water will emulsify with the oil and do BAD THINGS. Water-contaminated oil does adhere to surfaces as well, and bearings and gears don't live long without a protective film of petroleum.

After I was sure that there was no water in the oil, I changed the fluid one more time for luck, and set about insuring that I wouldn't have to repeat this exercise in the near future. That effort is detailed at the sister page to this, Extending Breather Hoses.