When your engine runs hot, the causes fall into a few categories. Here's how to narrow it down.
Check the reservoir and radiator (when cool). If low, you have a leak. Find and fix the leak before adding more—otherwise it just leaks out again.
Hoses, radiator, water pump seal, heater core, or head gasket. Look for puddles, drips, or white residue. Pressure test the system to locate small leaks.
Thermostat regulates flow. If stuck closed, coolant doesn't circulate—engine overheats. Replace thermostat; it's a common fix.
Pump drives coolant circulation. Bearing failure or impeller damage stops flow. Listen for grinding; check for seepage at the weep hole.
Old coolant, debris, or corrosion can restrict flow. Flush the system. If clogged internally, radiator may need replacement.
Coolant leaks into oil (milky oil) or combustion (white smoke). Compression test or chemical block test confirms. Expensive repair.
For the full engine systems picture—fuel, ignition, misfires—see our automotive engine systems guide.
Last updated: February 2026