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This question already has an answer here:

I have an Ibanez AW54-OPN and since I take lessons right after having finished my work day (5h) I was considering bring the guitar with me in the morning and leave it in a car (I'd prefer not to carry it with me at the workplace).

I live in northern Italy and temperatures span from -10 to 35 Celsius degree with an 80% average humidity.

By leaving the guitar in the car for 5 hours every two weeks do I risk ruining it?

marked as duplicate by Richard, MattPutnam, Shevliaskovic, leftaroundabout, Todd Wilcox Oct 10 '17 at 1:24

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  • Inside a car when it's 35C outside it'll end up even more than that inside. I've seen best part of 50C in my car in those conditions. No guitar of mine is going to be put through that! – Tim Oct 3 '17 at 16:11
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    A friend of mine related a story about taking a long trip with an acoustic guitar in the trunk of his car. The guitar was to be a gift for a young lady that had taken his fancy. When he presented the guitar to his lady friend, she opened the case to discover to his horror, that the guitar had literally fallen apart. I think the heat melted the glue holding it together. – Rockin Cowboy Oct 4 '17 at 0:31
  • Do you have case or gigbag? – el.pescado Oct 4 '17 at 5:46
  • @el.pescado gigbag – user36102 Oct 4 '17 at 14:58
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It's very bad practice to leave a guitar in a hot car for any amount of time, but the longer the time, the worse off your instrument will be, especially when the weather is hot. Five hours is absolutely too much.

When it's 35C (95F) outside, it's possible that your car is getting hot enough to melt hide glue, which is frequently used by luthiers and melts around 60 C (140F). Any part of your guitar that's held together with hide glue can loosen or come apart when the glue melts.

You are also risking cracking the wood because while the outside air is 80% humidity, the air in the overheated car is far drier, so your instrument is going through drastic changes in humidity, the perfect recipe to crack and warp it. Damage from this can be cumulative, with tiny invisible cracks forming, then eventually expanding as the instrument is further abused.

It's less dangerous in the cold, but the instrument is still subject to changing humidity as the car heats up.

A cheap plywood instrument mass produced with synthetic adhesives is less likely to be damaged, although it still isn't completely safe.

If you must leave the instrument in the car, park in the shade and leave the windows cracked. Put the instrument out of the sun, either in the trunk or under a blanket if you don't have a trunk. But bringing it with you is a much safer idea.

  • Keeping guitar in hardcase or at least in a gigbag might help too. – el.pescado Oct 4 '17 at 5:48
  • @el.pescado - gigbag is no help at all. A hermetically sealed hardcase (expensive) may help a little, but it's still not going to keep the guitar cool enough in that heat. Put anything in an oven for long enough, it'll get hot. – Tim Oct 4 '17 at 6:18
  • @Tim It may help retain humidity though. – el.pescado Oct 4 '17 at 6:28
  • @el.pescado, the problem is that hotter air can hold more water, so 80% humidity at 30C is a significantly percent lower humidity at 40 or 50C. It's like if you have a full glass of water and pour it into a bucket. The glass was mostly full, but the bucket with the same amount is mostly empty. – Karen Oct 4 '17 at 14:25
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Generally, keeping instruments in conditions outside of what we'd call normal room temperature and humidity for extended periods of time is best classified as a Bad Idea.

Cars are especially prone to heating up to temperatures far exceeding reported outside - especially when left out in sunlight. What effect does that have on instruments? It so happens I have an excellent example handy:

http://www.iommi.com/equipment/jaydee-custom-s-g-a-k-a-no-1-the-old-boy/

Tony Iommi's Jaydee Custom ("Old Boy") looks the way it does because the paint pretty much boiled off after being left in a car. Don't let the "extremely hot part of the world" bit fool you - an Italian summer could well produce similar conditions.

The Old Boy is, of course, an electric guitar and, therefore, much more robust. Extreme environmental changes will distress acoustic instruments in all sorts of interesting ways, both when heating up and when cooling down. Lasting damage could result.

Whilst keeping your guitar in the car may be more convenient, yes, you can ruin it that way.