How to make sure your vehicle is ready for hot summer driving:
Check the level and strength of the coolant. A low coolant level may allow your engine to overheat. Make sure the coolant reservoir is filled to the proper level. NEVER open a radiator cap on a hot radiator to check the coolant level! Hot steam and boiling coolant may spray out a burn you! Wait until the engine has cooled to check the level inside the radiator (this should not even be necessary if the coolant level in the reservoir is maintained). If low, add a 50/50 mixture of the specified coolant and water. NEVER run straight water in the radiator. Water does cool better than antifreeze, but antifreeze is required to raise the boiling temperature of the coolant and to protect against corrosion.
Make sure the cooling fan works. The electric cooling fan should come on when the air conditioner is turn on to MAX. No fan may mean a defective fan motor, relay or electrical problem. If the engine has a belt-driven fan with a fan clutch, a worn fan clutch may cause the engine to overheat. High mileage fan clutches (those with more than 100,000 miles on them) may be weak and not provide adequate cooling. If the fan clutch is leaking fluid or spins with little resistance, the clutch needs to be replaced.
Check your air conditioner. Make sure the A/C blows cold air and is working properly. Nothing makes hot weather seem worse as a weak air conditioner. If the A/C is not blowing cold air, the refrigerant charge may be low. The system should be checked for leaks before adding refrigerant.
Check the age of your battery. Most car batteries only last 4 or 5 years. If you battery is 5 or more years old, it will probably need to be replaced soon. Hot weather is actually harder on batteries than cold weather because it increases the rate of evaporation of the liquid electroyte inside the battery (this is not a problem with gel type batteries). The date can be determined by reading the date code on the battery. The date code number indicates the year, and the date code letter corresponds to the month (A = January, B = February, C = March, etc.)
Change the oil. Replacing old dirty oil with fresh oil can increase the lubrication protection for your engine. Switching to a heavier viscosity motor oil during hot weather is a good idea, especially on older high mileage engines. For example, you might want to change from 5W-30 to 10W-30, 10W-40 or 20W-30 for hot weather driving. Synthetic motor oils are even better for high temperature protection.
Check or replace the windshield wipers. Natural rubber wiper blades have a limited life of a year or less. Sun exposure, extreme heat and cold all age the rubber and cause it to become hard and brittle. If the wipers streak, chatter or smear, it is time to replace them.
Check Your Tires. Check the tire for wear, uneven wear, age cracks or damage. Check the inflation pressure in all the tiers, including the spare. Underinflated tires makes the tires run hot and increases the risk of a blowout.
Wax the body. The body should be waxed or sprayed with some type of protectant to help shield the paint from the ultraviolet rays from the sun, and summer smog in urban areas.
Keep your cool. Buy a sun shade for the windshield to reflect light so the interior doesn't get so hot if the vehicle is parked in direct sunlight. Also, close the sunroof sunshade, and leave the windows cracked so hot air can escape. This can lighten the cooling load on the air conditioner when the vehicle is first started, and prevent you from getting a hot seat or burning yourself on hot interior surfaces.
Protect yourself. Wear a hat to keep the hot sun off your head, especially if you are follically challenged (bald). Wear some sun screen, and carry a bottle of water in the car in case you get stuck for a long period of time in traffic or have a break-down on a hot day.