from Goss’ Garage by Pat Goss
Although probably not biblical this winter has been historic. Unfortunately snow measured in feet means many of you have accidentally damaged your cars. Although it’s a natural reaction wheel spinning in an attempt to keep moving can do a lot of damage.
Getting stuck happens but how you get unstuck could be costly. I’m sure you’ve read that rocking your car by shifting rapidly from drive to reverse is a good way to get yourself unstuck. True but there’s a deadly mechanical downside to it that no one ever mentions; transmission damage!
Automatic transmissions fluid is extremely sensitive to heat and is damaged or destroyed when it gets too hot. The issue relates to a phenomenon called oxidation that over time can really bite you financially. Oxidation occurs when oxygen is forced into union with the lubricants in the fluid. Slow oxidation over time is normal and is one of the main reasons transmissions must be flushed. But oxidation rates can be greatly accelerated by several different factors most notably high fluid temperature.
For every eighteen degrees of fluid temperature increase the fluid oxidation rate doubles and the life of your transmission fluid is cut in half. In other words the higher the temperature of your transmission fluid the shorter its life. Of course this doesn’t mean a couple minutes of severely high temperature will immediately kill your fluid but the effect is cumulative so even one instance sets the process in motion.
Getting stuck or spinning your wheels causes high transmission fluid temperature. That’s because a car that’s stuck is standing still so there is no air moving around the transmission or through the radiator to keep the fluid cool. Although the cooling fan may be running it isn’t designed to control the high heat loads produced by wheel spin so the fluid keeps getting hotter and hotter. The longer you rock the car, the longer you spin the wheels or the faster you spin the wheels the hotter the transmission fluid becomes.
Long periods of wheel spinning will cause the fluid to become so hot it will warp parts inside the transmission killing it. But much more common is fluid oxidation which if left untreated also will ultimately cause transmission failure. How quickly will the transmission fail? That depends on several factors. The damage could be minor and hurt nothing for years or it could be severe and kill the transmission in minutes.
When transmission fluid consistently operates at 180 degrees or less it could last up to 60,000 miles. But that isn’t going to happen. Hot days in heavy traffic, towing, heavy loads, hard acceleration and numerous other routine driving situations will push the temperature above the magical and safe 180 degree mark. That’s why we recommend a BG transmission flush every 30,000 miles or sooner.
If your wheel spinning exercise causes the fluid to hit 220 degrees its life could be reduced to 15,000 miles. Sadly wheel spinning usually pushes fluid temp up to 240 degrees or higher where fluid life drops to a mere 7,500 miles. And if rocking or spinning heats the fluid to 260 degrees its life is a startlingly low 3.750 miles. But then there are the cowboys and idiots who go Postal with wildly spinning tires literally screaming for mercy. Their fluid could easily climb to a blistering 300 plus degrees. Unfortunately for them the life of their transmissions might be measured in minutes.
There may be more snow coming so if you get stuck take it easy; allow the transmission to cool for at least five minutes after thirty seconds of rocking or spinning. After an incident, always have the fluid condition checked and preferably flushed or best of all call road service. Pat Goss
© Copyright 2/16/2010 Pat Goss. All Rights Reserved.