Why can't I leave my instrument in the car? - Jul 2001
The details are different in hot weather than in cold weather, but the short answer is that your instrument can be irreparably damaged if it experiences drastic temperature extremes, especially if the temperature change is sudden.
Your car, the air around it & the pavement on which it rests absorb energy from sunlight & turn it to heat. In cold weather, the already cold surfaces disperse the heat, & the inside of the car stays cool In hot weather, the air, the pavement & the car all get warmer & warmer, with nowhere for the heat to go. The inside of the car gets HOT...FAST!
With sufficient heat, the glues used in instruements becomes soft & rubbery & string tension can literally pull the instrument apart. The neck rotates forward in its block, & can even come completely off of the instrument. Glued-on bridges lift at the back edge, or come off completely. Braces inside of the top & back of the instrument loosen or separate completely from the surfaces that they're designed to support; the sides of the instrument begin to straighten, separating from the top & back of the instrument. At a high enough temperature, the damage can happen in just a few minutes. On an 85 F day, for example, the temperature inside your car (with the windows opened slightly) can reach 102 F in 10 minutes and 120 F in half an hour. Warmer days will drive the temperature in your car even higher. The glue used to make violins becomes a runny liquid at 140 F, & becomes rubbery & weak before it gets that hot. So, your Stradivarius could turn into junk in under 15 minutes. And, while glues used in guitars and mandolins soften at slightly higher temperatures, string tension on those instruments is much higher. So damage can occur as quickly. The day doesn't have to be very hot & the errand doesn't have to take very long to incur damage.
Even if the instrument doesn't come apart, lifting of the bridge & rotation of the neck (that isn't obvious visually) can make the instrument unplayable (because the strings raise higher from the fingerboard). Resetting the bridge costs at least $80 & a neck reset represents more than $200 out of your pocket (the repair is not covered by warrantee if you melted the neck off in a car).
If you do inadvertently leave an instrument in the car, realize that it's gotten hot, run out to the car and grab the case...don't open the case if the case feels hotter than the surrounding air. The finish shrinks faster than the wood. So, held in tension at the bond to the wood, the finish attempts to shrink, but is forced to crack to do it. If the case is warm or hot to the touch, take it to a cool location & let it cool to room temperature before you open it. If heat has caused damage, the odds of the damage getting much worse as the case cools are lower than the odds of the finish cracking if a quick temperature change shocks it.
When you can safely open the case, check the neck angle, bridge/belly joint & seams. Tap the top & back of the instrument & listen for rattles that suggest that braces have come loose inside. If everything looks O.K., & the instrument plays well, be thankful & sin no more. If you notice any problems with the bridge, seams, braces or playability, take the instrument to a qualified repair person for more thorough examination & any necessary repair.