A car that handles the daily commute without complaint can behave very differently on a 600-mile drive in July heat with the AC running and a full load of luggage. The components that fail on long trips are usually ones that were marginal already, pushed past their limit by sustained load and temperature.

Battery and charging system

Battery failures spike in summer, not winter. A battery that's borderline will start the car fine on a cool morning but fail on a hot afternoon when the engine is warm, the AC is running, and the alternator is working hard. A battery load test takes about five minutes and tells you whether the battery has enough reserve capacity for sustained use. If the battery is more than four years old and hasn't been tested recently, test it before a long trip.

Tires, including the spare

Check tire pressure when the tires are cold, before you've driven more than a mile. Hot weather increases pressure, and underinflated tires run hotter, which accelerates wear and increases blowout risk on long highway stretches. Check tread depth on all four tires and look for uneven wear, which indicates an alignment or suspension issue. Then check the spare. The spare is almost always forgotten. A flat spare on the side of a highway in July is a bad situation.

Coolant and hoses

Coolant concentration should be checked with a refractometer, not just by looking at the level. Old coolant loses its corrosion inhibitors and can cause internal damage to the cooling system over time. Hose condition matters too. A hose that looks fine can be soft and spongy internally, close to failure under sustained heat load. Squeeze the hoses when the engine is cold. They should feel firm, not mushy.

Serpentine belt

The serpentine belt drives the alternator, power steering pump, AC compressor, and water pump on most modern engines. A belt that's cracking or glazing can fail without much warning. On a long trip, a failed serpentine belt means no charging, no power steering, and an overheating engine within minutes. Belts are inexpensive to replace preventively. They're expensive to deal with on the side of a highway.

Brakes

You don't need perfect brakes for a road trip, but you need brakes that are adequate for sustained use. Brakes that are marginal on the daily commute can fade on a long downhill grade with a loaded car. Have the pad thickness checked and ask about rotor condition. If you're close to the wear limit, replace them before the trip rather than after.

A pre-trip inspection at the shop runs $65 to $95 and covers all of the above. We're booking into mid-July for summer slots. Call ahead if you want a time before the holiday weekend.