Engine Warm-up

Driving gently warms engines faster than idling. The thermostat controls warm-up. Oil warms more slowly than coolant. Many cars show a blue coolant symbol or a low gauge reading until warm, and some limit maximum revs during warm-up. Frequent short trips where the engine never warms up lead to condensation in the oil and exhaust, which promotes sludge and corrosion. Idling to warm up wastes fuel and is restricted in some cities.

Heat from combustion raises temperatures.

Slow warm-up can mean a stuck-open thermostat. Avoid heavy loads until warm.