How do you know if your radiator is blocked?

Answer 1

- Engine temperature is high - Could also be the thermostat (if no heat from heater) - It is possible to see the fluid flow by removing the radiator cap and looking in. How: Do not do this if the engine is hot or if the engine was recently run. Let the engine cool for 3 hours first. Remove the cap when the engine is cold. Start the engine. As the engine heats up (maybe two minutes) the thermostat will (should) open and you should see fluid flowing. May need a flash light to see into the radiator. - If some of the narrow channels in the engine block are clogged you may hear the radiator boiling after the engine has turned off.