Cosmoline on a Transmission? Anyone? Options

[detoxcowboy]

I just read in the vendors section of Cosmoline being used to coat a transmision for protectiveness after being cleaned.. Has anyone used this before? How does it hold up? (apperently it is used for fire arms and automotive, available in aresol and bricks)

Curious as I recently replaced my transmission and now have a very cleaned case..


Cosmoline is the trade name for a generic class of rust preventatives, conforming to MIL-C-11796C Class 3, that are a brown colored wax-like mass; have a slight fluorescence; and have a petroleum-like odor and taste (as detected when working with it).

Chemically, cosmoline is a homogeneous mixture of oily and waxy long-chain, non-polar hydrocarbons. It is always brown in color, but can differ in viscosity and shear strength. Cosmoline melts at 113-125 °F (45–52 °C) and has a flashpoint of 365 °F (185 °C).

Its most common use is in the storage and preservation of firearms. Previously, cosmoline was used to preserve other items. Entire vehicles can be preserved with cosmoline.

[Richard Casto]

I just read in the vendors section of Cosmoline being used to coat a transmision for protectiveness after being cleaned.. Has anyone used this before? How does it hold up? (apperently it is used for fire arms and automotive, available in aresol and bricks)

Curious as I recently replaced my transmission and now have a very cleaned case..

I am not sure, but you might be referring to my recent post in the vendor section. I mention that I use Tectyl to coat transmissions that are cleaned as part of my rebuild process.

Magnesium does oxidize so that is why bare Magnesium needs to be protected. Like aluminum, it does create a thin layer of oxidation. But while Aluminum Oxide is very strong and prevents additional corrosion, I don’t think that Magnesium Oxide is very strong and doesn’t provide as much protection. So you will see Magnesium corrode away much faster than Aluminum. I also suspect part of the issue is where Magnesium falls on the galvanic chart. It is below Zinc, so it makes a perfect sacrificial anode and corrodes away before other metals such as steel. Hot water tanks usually have a sacrificial Magnesium anode to prevent corrosion of the steel tank and fittings.

I need to post a photo of a case I just took apart. The differential cover (on the inside) has a deep bit of corrosion. I would like to talk to a chemist or metallurgists about this, but I suspect it might be something like how mercury is the arch-enemy of aluminum. If you have not seen this before, you should watch how mercury prevents that thin layer of Aluminum Oxide from stopping additional oxidation.

http://www.youtube.com/watch?v=Z7Ilxsu-JlY

I suspect that something (maybe mercury?) has a similar effect on Magnesium. Sometimes you will see an area that is fine and right next to it deep corrosion as if something broke that Oxide barrier. Some people call that "worm" corrosion as it looks like a worm ate holes or paths in the Magnesium.

Anyhow, if you don’t use something like paint or a modern aerospace coating, your transmission case will slowly corrode over time if left unprotected. When I rebuild a case, I clean it for my customers. While a greasy case does provide some level of protection, every case I have seen has some level of corrosion going on even when covered in grease. Basically I don’t believe in leaving it greasy as a way to protect it. Paint or a spray on coating is much better at coverage than incidental grease.

By default I do not media blast and then paint the cases I work on (this can be done at extra cost.) But as part of a normal rebuilt, I clean and then spray with Tectyl which is a Cosmoline “like” product. “Cosmoline” is just a trade name of a Mil Spec waxy coating (Sort of like how “Xerox” ended up being a generic name for photocopy.) Tectyl is the brand that was used by the factory to protect the assembled transmission. I was able to source some, so that is what I am using as well. I figure if it was good enough for the factory, its good enough for me and my customers. Event today there are various Tectyl products aimed at the automotive industry.

Regarding how well something like Tectyl lasts, I have done some testing on this. Any spray on waxy coating is not going to last forever. If exposed to the elements it eventually gets worn away. Nook and crannies as you would expect last much longer, but the coating on edges and ridges in the casting wear off first. I have run some tests and I would say that the coating provides protection in the “months” range and not in the “years” range. I would go beyond a year, but my test case hasn’t run that long yet.

While I use Tectyl, I think the CRC Marine Heavy Duty Corrosion Inhibitor is good stuff as well and is probably easier to find. In fact, I suspect it might be a Tectyl clone, or even a repackaging of Tectyl.

You can clean this stuff off with Brake Cleaner or Mineral Spirits.