Both high and low environmental temperatures can present problems with belt drive systems.
In general, the maximum recommended temperature for belt drive systems for standard belts is 185 deg. F (85 deg. C). For rubber belts, temperatures exceeding this can result in gradual compound hardening and eventual cracking as belts stiffen. For urethane belts such as Poly Chain GT Carbon, the urethane will may begin to soften and will eventually melt at temperatures exceeding 200 deg. F (93 deg. C). There are a few options for belt drives operating in high temperature applications, but belts made from materials with higher temperature resistance are still limited to a maximum temperature of about 230 deg. F (110 deg. C).
Belts can "overheat" from slippage even when environmental temperatures are not excessively hot. If belts are hard and appear glazed from heat, always check to make sure the tension is at the recommended level, and that sheave grooves are not worn excessively. In most normal environments, belt surface temperatures do not typically exceed 120 deg. F (49 deg. C) or so.
Belts are generally limited to a minimum temperature of about -30 deg. F (-34 deg. C). Rubber belts operating in temperatures lower than this can harden and crack. Cold soaked belt drive starts are especially vulnerable to belt cracking. Poly Chain GT Carbon belts are capable of operating at temperatures down to -65 deg. F (-54 deg. C).