My car heater is taking a long time to come on if at all. Anyone know what can be causing this?

Just to note that I recently changed my engine because the previous engine overheated and the water pump was found to be not working.

  • Too long as in how many minutes?
    – Chris H
    Commented Nov 29, 2017 at 11:41
  • There is a good chance it is now working correctly as on the previous engine, it was overheating significantly meaning there was lots of heat available in the cabin. Commented Nov 29, 2017 at 13:26
  • What do you mean "come on"? Do you mean before you feel the heat? Or do you mean the fan blowing?
    – CharlieRB
    Commented Nov 29, 2017 at 14:39
  • What car is this? My car doesn't have electric heating elements, and just blows engine heat at me. This means the max temperature it will blow is determined by how warm my engine is. You say your previous engine overheated, so it's possible you also don't have electric heating elements, and you were used to the overheating(!) engine's heat. Commented Nov 29, 2017 at 15:29

4 Answers 4


When the engine was changed, was the heater properly bled when the cooling system was refilled? If there is an air-bubble stopping coolant from flowing properly through the heater, that would create exactly the symptoms you are describing, yet may not cause any overheating issues if the rest of the cooling system is working correctly.

  • 1
    Actually just returned from the mechanic. They identified a leak in the radiator and said the thermostat needs changing but can't remember the reason for the latter. This could have been the reason why my engine originally overheated and hence I had to replace it, however if so seems the mechanic didn't bother to find out why the original engine overheated. Commented Nov 29, 2017 at 15:15
  • 1
    Not changing the thermostat when changing the engine (if that's what they did) was a dumbass move by the mechanic - even if they didn't suspect a problem with it they are so cheap that it's a false economy putting the old one back on! It's worth noting though that a thermostat stuck "open" wouldn't cause a car to overheat (at least not on it's own). Commented Nov 29, 2017 at 15:29
  • @motosubatsu right, they didn't change the thermostat. but i think not checking for leaks(which was the original cause for the original engine to overheat) is even more dumb ass. it's unforgivable. had i not realised some problem was developing, wouldve ended up with a damaged engine again. Commented Nov 30, 2017 at 7:39

In addition to Nick C's excellent suggestions there is also a possibility that the thermostat is stuck in the "Open" position - this would mean that coolant is always circulating around the radiator (rather than only once it has reached temperature) which would cause it to take a much greater length of time to come up to temperature (and consequently provide heat to the cabin)

  • On some engines its possible to just not install a thermostat especially if hoses and housings were all opened up for an engine swap. Good point.
    – JPhi1618
    Commented Nov 29, 2017 at 15:27

A car heater can stop working for a number of reasons including a low antifreeze/water level in the radiator(due to leaks in the cooling system) or a bad thermostat which isn't allowing the car to heat up properly etc.

In this case it was due to a low antifreeze/water level in the radiator due to a leak. It was not related to the new engine installation but it seems this leak was the cause for the overheating of the original engine however the technician didn't test for/fix the leak after the new engine was installed. 'New' mechanic also suspected a problem with and changed the thermostat.


Once your car becomes overheated, I think you must change your heater coil also, because if the heater coil is partially blocked taking too much time for heater coil became heat :)


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