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lubricant degradation over time(5 posts)

lubricant degradation over timexxl
Sep 30, 2003 6:57 PM
So, I'm overhauling a friend's clunker the other day, and this bike is an old one, Ultra-6 drive, with maybe twenty miles on it; rusted-yet-new chain, tire nibs over rotten sidewalls, etc. As I'm dutifully changing the old-but-clean grease in the hubs, my young daughter asks me why I need to do so, since the grease that was already in there was practically unused. I replied that the old grease had "decomposed over time," which was not a very satisfying answer, really, and got me thinking "what does happen to essentially unused grease, anyway, that I feel I need to change it out? After all, the stuff sits in the grease gun or can for years, and in the ground for millenia before that, with no apparent harm, so why should it go bad just sitting in some bearing races? I understand how use and contamination degrades lube, but this stuff was so obviously unused, OEM stuff. So, anyone know the chemistry at work here? Or, could I really have just skipped the relube?
wondered the same thing, so I got an oil PR guy's opinionCory
Sep 30, 2003 7:13 PM
I wondered the same thing about my daughter's unridden-for-six years mountain bike. The grease LOOKED new, and it only had a few miles on it. Friend of mine is a PR guy for an oil company (not an engineer or anything, a flak), so I asked him. He said the lighter, thinner lubes might suffer some degradation in a process similar to what happens to gasoline--the light ends of the molecules cook off over time, so the properties change. He theorizes, somewhat knowledgeably, that that could happen very slowly to thin lubes, but with grease it's probably measured in geologic time.
Evaporation & OxidationJimP
Oct 1, 2003 8:06 AM
The grease in the gun or can is sealed where the grease in even a "sealed" bearing will have the lighter parts evaporate. You see grease that has set in a partially filled can get thicker and finally set up like caulking compound.

Evaporation & Oxidation - Jim P has got it right! (nm)Kerry Irons
Oct 1, 2003 5:07 PM
re: lubricant degradation over timeHot Carl
Oct 1, 2003 2:46 PM
I had a tube of Phil Grease go bad. It somehow seperated so that a watery substance comes with the grease. It's sort of like how catsup separates.