You may not have heat issues but humidity. Which can cause aging and failures.
I'd move the router up into the home and try again.
Over the past week, our wireless router has been randomly throttling our internet speeds from around 25mbps to 3. Just earlier after power cycling the router, it ceased connecting to the internet. It still puts out a signal I can connect to, there's just nothing behind it.
Yet if I plug everything into our ISP provided router, it works fine (i.e. it's not an issue with the cabling). Awful signal strength, but it's usable. This is the fourth or fifth router that has done this in as many years. They have all been kept in a well ventilated area in the basement, which is kept fairly cool year round. Why does this keep happening?