03 civic ex 232,000 miles on it - heat not heating at idle, yet will heat when driving. What's up? heater core, thermostat or head gasket?
1 Answer
More like water pump. The vanes wear down and/or corrode and it can no longer make enough flow at lower RPMs. Check all the hoses too, make sure none of them have collapsed (esp. the lower radiator hose), the heater hoses should feel pressurized and how to the touch when engine is running at temperature. At your mileage that water pump, assuming it has never been changed, has to be on it's last leg.