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Driving in very hot weather

General Knowledge3 minManual section 2.14

Heat is hard on tires, engines and cooling systems. Learn what to check, why you must never let air out of hot tires, how to open a radiator safely, and how to drive to prevent overheating.

Tires, oil and belts

Do a normal vehicle inspection, with special attention to these items.

  • Tires: check tire mounting and air pressure. Inspect tires every 2 hours or every 100 miles in very hot weather. Heat makes air pressure go up. Never let air out, because once the tires cool the pressure will be too low. If a tire is too hot to touch, stay stopped until it cools; otherwise it may blow out or catch fire.
  • Engine oil: oil helps cool the engine as well as lubricate it. Make sure there is enough. If you have an oil temperature gauge, keep the reading in the proper range while driving.
  • Engine belts: learn how to test V-belt tightness by pushing on each belt. A loose belt cannot drive the water pump and/or fan correctly, so the engine overheats. Also check belts for cracks and other wear.
  • Hoses: coolant hoses must be in good shape. If a hose bursts on the road, the engine can fail and may even catch fire.

Engine coolant and the radiator cap

Before starting out, make sure the cooling system has enough water and antifreeze as the engine maker directs. Antifreeze helps the engine in heat as well as cold. While driving, check the water or coolant temperature gauge from time to time. If it goes above the highest safe temperature, something may be wrong that could cause engine failure and possibly fire. Stop as soon as safely possible and try to find the problem.

Some trucks are fitted with sight glasses, clear coolant overflow containers, or coolant recovery containers. With these you can check coolant while the engine is hot. When such a container sits outside the pressurized system, its cap can be removed safely and coolant added even at operating temperature.

Do not open the radiator cap or any other part of the pressurized system before it has cooled. Pressurized steam and boiling coolant can shoot out and cause severe burns. A cap you can hold with your bare hand is probably cool enough to open.

To add coolant to a system without a recovery or overflow tank:

  • Shut the engine off.
  • Wait until the engine has cooled.
  • Protect your hands with gloves or a thick cloth.
  • Turn the cap slowly to the first stop, which releases the pressure seal.
  • Step back while pressure is released.
  • Once the pressure is gone, push down on the cap and keep turning until it comes off.
  • Look at the coolant level and add more if needed.
  • Replace the cap and turn it all the way to the closed position.

Driving in the heat

  • Watch for bleeding tar. In very hot weather, tar in the pavement often rises to the surface. Spots where tar "bleeds" through are very slippery.
  • Keep your speed down to avoid overheating. Driving fast makes the tires and engine hotter. In desert conditions, heat can build to a dangerous level and raise the chance of tire failure, fire, and engine failure.

References and scope

The topic reference is listed below. Sources support verification; the lesson itself is here. The current content needs technical and language review before public launch.

Manual reference: 2.14

Official CDL handbook · Utah ↗StatesOur editorial approach

Put it into practice

Educational questions with explanations. The answer review also works without the interactive quiz.

Preparing your questions…

Review questions with answers

  1. In very hot weather, how often should you inspect your tires?
    1. Once a day
    2. Every 2 hours or every 100 miles
    3. Every 500 miles
    4. Only at the start of the trip
    Show answer
    Every 2 hours or every 100 miles

    In very hot weather, check the tires every 2 hours or every 100 miles.

  2. Hot tires show higher pressure than normal, so you should bleed off air until the gauge reads normal. True or False?
    1. True
    2. False
    Show answer
    False

    False. Air pressure rises with heat. If you let air out, the pressure will be too low when the tires cool.

  3. A tire is too hot to touch. What should you do?
    1. Pour cold water on it and drive on
    2. Let some air out
    3. Drive faster to cool it with air flow
    4. Remain stopped until the tire cools off
    Show answer
    Remain stopped until the tire cools off

    If a tire is too hot to touch, stay stopped until it cools; otherwise it may blow out or catch fire.

  4. Besides lubricating the engine, engine oil also helps to:
    1. Keep the engine cool
    2. Charge the battery
    3. Clean the windshield
    4. Inflate the tires
    Show answer
    Keep the engine cool

    Besides lubricating, engine oil carries heat away and helps cool the engine.

  5. Antifreeze in the cooling system:
    1. Is only needed in winter
    2. Should be drained in summer
    3. Helps the engine in hot conditions as well as cold
    4. Lowers oil pressure
    Show answer
    Helps the engine in hot conditions as well as cold

    Antifreeze helps the engine under hot conditions as well as cold ones.

  6. While driving, the coolant temperature gauge goes above the highest safe temperature. You should:
    1. Turn off the air conditioner and keep driving
    2. Remove the radiator cap right away
    3. Speed up to get more air through the radiator
    4. Stop driving as soon as safely possible and find out what is wrong
    Show answer
    Stop driving as soon as safely possible and find out what is wrong

    A high reading may mean a problem that could cause engine failure and possibly fire. Stop as soon as safely possible.

  7. If the engine is not overheating, it is safe to open the radiator cap while the system is still hot. True or False?
    1. True
    2. False
    Show answer
    False

    False. Do not open the radiator cap or any part of the pressurized system until it cools; pressurized steam and boiling coolant can cause severe burns.

  8. A quick way to tell if the radiator cap is probably cool enough to open is:
    1. The engine has been off for 1 minute
    2. You can touch the cap with your bare hand
    3. The temperature gauge reads normal while driving
    4. Steam has stopped coming from the hood
    Show answer
    You can touch the cap with your bare hand

    A cap you can hold with your bare hand is probably cool enough to open.

  9. When adding coolant to a system without a recovery tank, after the engine has cooled and your hands are protected, you should first:
    1. Remove the cap in one fast turn
    2. Start the engine
    3. Turn the cap slowly to the first stop to release the pressure seal, then step back
    4. Add coolant through the overflow hose
    Show answer
    Turn the cap slowly to the first stop to release the pressure seal, then step back

    Turn the cap slowly to the first stop to release pressure, step back, then press down and turn to remove it.

  10. Some vehicles have see-through coolant recovery containers. If the container is not part of the pressurized system:
    1. Its cap can be removed safely and coolant added even when the engine is hot
    2. It must never be opened
    3. It can only be filled with water
    4. It shows the oil level
    Show answer
    Its cap can be removed safely and coolant added even when the engine is hot

    If the container is not part of the pressurized system, its cap can be safely removed and coolant added even at operating temperature.

  11. Loose engine belts can cause overheating because:
    1. They make the oil too thin
    2. They block the radiator
    3. They drain the coolant
    4. They will not turn the water pump and/or fan properly
    Show answer
    They will not turn the water pump and/or fan properly

    Loose belts will not turn the water pump and/or fan properly, which results in overheating. Check tightness by pressing on the belts.

  12. A broken coolant hose while driving can lead to:
    1. Better fuel mileage
    2. Engine failure and even fire
    3. Lower tire pressure
    4. Wet brakes
    Show answer
    Engine failure and even fire

    If a coolant hose bursts on the road, the engine can fail and may even catch fire, so check hoses for good condition.

  13. In very hot weather, spots where tar "bleeds" to the road surface are:
    1. Safe and give extra grip
    2. Only a cosmetic problem
    3. Very slippery
    4. Found only on gravel roads
    Show answer
    Very slippery

    Tar often rises to the surface in very hot weather, and these bleeding spots are very slippery.

  14. Why should you go slowly enough in desert heat?
    1. High speeds create more heat for tires and the engine, raising the chance of tire failure, fire and engine failure
    2. Slow speeds save brakes for mountains
    3. Speed limits are lower in deserts
    4. Fast driving wears out windshield wipers
    Show answer
    High speeds create more heat for tires and the engine, raising the chance of tire failure, fire and engine failure

    High speeds create more heat; in desert conditions it can build up to a dangerous point and increase tire failure, fire and engine failure.