This summer, the U.S. has experienced two significant heat-wave events, impacting the Midwest, South, Mid-Atlantic, Northeast, and the West. And it's well known that summer's hottest temperatures can arrive well after the season begins and linger through September. As temperatures remain high, the risk of unexpected breakdowns continues to increase, placing greater demands on both vehicles and drivers.

Prolonged summer heat places continuous stress on vehicle systems over weeks or even months, making small maintenance issues more likely to develop into costly roadside failures, such as tire blowouts or engine overheating.

These unexpected roadside repairs also carry a significantly higher price tag than scheduled preventative maintenance performed in a controlled shop environment. Emergency labor rates, towing costs and operational disruptions can quickly escalate repair expenses.

The repair itself is rarely the biggest number. Fleets in Cox Automotive's proprietary fleet research put the cost of pulling a single heavy-duty vehicle out of service for 24 hours at roughly $1,500 to $1,650 for small and medium fleets, and $2,200 to $2,700 for large fleets. Asked why downtime is so hard to manage, half point to the same thing: lost revenue from vehicles sitting.

Aside from ERS costs, a single roadside breakdown can disrupt operations. Extended downtime on one vehicle could mean delayed deliveries and the need to shuffle schedules.

At the same time, increased seasonal demand for maintenance providers and replacement parts may extend repair timelines, making it even more difficult to return vehicles to service quickly. More than a third of fleets cite limited spare vehicle availability to cover outages, and more than a third cite delays coordinating vendor response, as reasons downtime is difficult to control.

The good news is that many of the most common summer breakdowns are preventable with proactive maintenance and routine inspections throughout the season.

In extreme heat, proactive maintenance matters

Preventative maintenance isn't a one-time task completed before summer begins. As extreme temperatures persist, maintenance strategies should continue evolving alongside operating conditions.

Vehicles that were inspected prior to or earlier in the summer have now endured weeks of elevated temperatures, increased mileage, and heavier workloads. Continuous exposure to high temperatures accelerates wear on the components already working hardest: radiators and charge air coolers, coolant hoses, belts and fan clutches, batteries, tires, A/C compressors and seals, electrical connections, and reefer units running near-continuously to hold temperature. Modern emissions systems compound it. Aftertreatment throws off significant additional heat, so today's cooling systems carry more thermal load than the equipment many fleets ran a decade ago. Something as small as a radiator screen packed with summer bugs and road debris can be the difference between a functioning cooling system and a derate on an on-ramp.

This makes routine inspections throughout the season just as important as preseason preparation.

One way to mitigate risk is to schedule preventive maintenance between peak operating periods whenever possible, increase inspection frequency during prolonged extreme heat, and prioritize cooling systems, tires, batteries, and other components that experience additional stress during extreme temperatures. Drivers also play an important role by reporting changes in vehicle performance as soon as they notice them, allowing maintenance teams to address potential problems before they escalate.

Telematics should be carrying part of that watch. Coolant temperature trends, fan clutch behavior, and heat-related diagnostic trouble codes can surface a developing problem days before a driver feels it. A coolant temp that climbs a little higher on the same grade every afternoon is a story worth reading.

Planning ahead is equally important. Summer often brings increased demand for maintenance providers and tighter parts availability, making it more difficult to complete repairs quickly when breakdowns occur.

Maintenance items to focus on as mercury rises

Many heat-related breakdowns begin with maintenance issues that could have been identified during routine inspections. During extended periods of extreme heat, even well-maintained vehicles experience additional stress, making those inspections even more valuable.

For example, checking transmission fluid levels becomes more important in hot weather, as the gears already generate a lot of heat during normal operation.

Cooling systems deserve particular attention. Aging hoses, worn belts, low coolant levels, and restricted airflow may not immediately affect vehicle performance under normal operating conditions, but sustained high temperatures can quickly expose those weaknesses. Cooling system inspections become especially important during prolonged heat waves, as overheating remains a common cause of summer roadside breakdowns. Keeping radiators and coolers clean and confirming that fan clutches are actually engaging are two of the least glamorous and highest-yield checks on the list.

Tires should also remain a priority throughout the season. Sun-baked asphalt with hot ambient air can reach up to 140 degrees F, placing significant stress on tires, making proper inflation and tread depth increasingly important as summer progresses.

Heat also distorts what a gauge tells you. TMC's recommended practice notes that pressure can rise 10% to 15% from normal warm-up, which makes a hot-tire reading a poor substitute for a cold-tire check against load. That distinction matters, because underinflation rather than tread wear is what usually turns a tire into a roadside event.

For semi-trucks, another important consideration is that tires vary significantly depending on the region's climate. If fleet routes change between spring and summer—for example, from mixed terrain to the Southwest—tires should, too. And they should be appropriate for the region and climate.

Battery health is another commonly overlooked area. Although battery failures are commonly associated with cold weather, prolonged exposure to extreme heat can be just as damaging, accelerating internal wear and shortening battery life. Ask an experienced technician about batteries, and you'll get some version of the same story: heat is what kills them, and cold just exposes the damage. A battery that spent July baking in a yard outside Phoenix doesn't quit in July. It's also why a lot of fleets in hot climates stop pushing batteries to failure and just plan on pulling them around the four-year mark. Routine load testing and charging system inspections help identify weakening batteries before they fail unexpectedly.

Air conditioning systems also contribute to safe fleet operations. Maintaining a comfortable cab environment helps drivers remain alert and focused during long shifts in high temperatures, reducing fatigue and supporting safer driving conditions.

A technician running a summer A/C check is reading high- and low-side pressures and vent temperature, checking for leaks and correct refrigerant charge, cleaning the condenser and cab air filter, verifying blower and blend door operation, confirming belt tension and clutch engagement, and clearing the condensate drain. During sustained heat, every 30 days is a reasonable cadence. A/C is also one of the harder systems to repair well on the roadside, and those calls tend to arrive at 2 or 3 a.m. when local shops are already backed up.

Compared to the operational disruption of an unexpected roadside breakdown, these inspections require relatively little time while helping fleets reduce risk throughout the remainder of the summer.

Dive into proactive maintenance

Summer operating conditions leave little margin for preventable failures. Many of the most disruptive heat-related breakdowns can be avoided through proactive inspections and preventative maintenance performed throughout the season.

By identifying maintenance concerns before prolonged heat exposes them, fleets can reduce downtime, improve safety and better protect drivers, customers and day-to-day operations. Those efforts also support compliance while helping vehicles remain reliable during one of the hottest times of the year.

The habits fleets establish during the summer—consistent inspections, proactive repairs and early identification of developing issues—also create a stronger foundation heading into fall and winter operations.

In an industry where uptime is critical, preparing for extreme heat is more than maintaining vehicles. It's about protecting drivers, meeting customer expectations, and keeping fleets moving when reliability matters most.