There heat for the car interior is on the outer coolant loop, compared to the inner coolant loop designed to warm the engine up rapidly. Inner loop is simpy the engine block and excludes the radiator. Outer loop contains everything else.
Right, if the car is taking ages to warm up, but the engine temperature is fine and shows as being warm relatively quickly, chances are is that you have an air lock in the system. Bleeding it should remove the air lock and return heat to the car interior (it has its own small radiator). If you've had work done recently or had to top up the coolant, then this is more likely.
If the car is warming up as normal, check that the radiator is hot or not (be careful as it can get quite toasty). If it's hot then its more likely to be an air lock, if its cold, then it is more likely that either the water pump or thermostat isn't working.
If the car is taking ages to warm up (shown by the engine temperature), then possibly the thermostat is broken and not restricting the water flow to the inner loop whilst the car is still cold. Lots more water to heat and possibly you could finish your journey before it has heated up.
Jim, October 2010
