Five tips for driving in extreme heat (via Forbes):

1. Battery. Most of us know that cold weather can cause a car battery to fail, but hot weather is almost as brutal. If you still have a serviceable wet cell battery, bring fluids and electrolytes to their proper levels. If you have a maintenance free wet cell, a gel cell or absorbed glass mat (AGM) battery, look them over to be sure that they
haven’t cracked or leaked. For all types of battery, clean any corrosion from the terminals, secure all connections and assure that the battery is firmly mounted and safe from vibration.
2. Cooling System. The coolant in your radiator should be flushed and replaced on a periodic basis – check your owners manual for details. In between, check the level of fluid in your cooling system by looking for the plastic overflow tank under your hood. If the level is low, add the recommended fluid before driving. Don’t try to open the radiator cap on your car until the engine has cooled down — you’ll release hot steam, and possibly boiling fluid, into the air. Very dangerous. Wait for things to cool down. Check all of your radiator hoses and connections. If a hose feels spongy, replace it before it bursts. If a connection is loose, tighten it.
3. Tires. Make sure that your tires are properly inflated before you head out for a drive. Under-inflated tires are subject to excessive friction, which causes heat. If conditions are already hot, under-inflated tires are even more likely to fail. Beware over-inflation as well. Air expands with heat, so slightly over-inflated tires can become dangerously over-inflated in hot weather driving. Not good. Don’t forget the spare, if your car has one.
4. Engine Fluids. Hot weather driving puts heavy demand on all of your engine’s components, not just your cooling system. Check your engine oil, transmission fluid, power steering fluid and brake fluid to make sure that they’re all at the recommended levels.
5. Air conditioning. According to the Auto Club of Southern CA, “Cool passengers are happy passengers.” If you’ve noticed that your car air conditioning isn’t working as well as it has in the past, take it to a certified technician and have the system checked out. While they’re at it, have them replace the cabin air filter, if it hasn’t been done within the past six months.