This is a curiosity question. I recently had the timing belt, tensioner and water pump replaced on my Honda Odyssey.

When I picked up the van it was really hot inside but I didn't think much of it. Later I turned on the climate control and noticed the mechanic had set it to 34c and apparently ran it long enough to really heat up the interior.

Is this a standard test of some kind related to either the coolant change or the other items that were serviced? And assuming it is, what is the goal?

  • 6
    Maybe they where just cold.
    – narkeleptk
    Apr 11, 2021 at 19:48
  • Yeah I considered that, part of why I'm curious :) Apr 11, 2021 at 21:14

1 Answer 1


If the cooling system is drained, it needs to be refilled and all air needs to be removed. The mechanic turns the heater on to allow coolant through the heater core to be sure all air is being removed. It's part of the burping process.

  • 3
    Just to make sure I'm following this, the engine coolant circulates through the climate control system to generate the heat used for comfort heating, so by cranking the heat you get max circulation through the heater core and make sure any air is pushed out? Apr 11, 2021 at 21:13
  • 3
    Correct. In fact you need to turn the heater control full on while refilling the system, otherwise the heater core will remain full of air which will form an airlock preventing any coolant circulating through the heater.
    – alephzero
    Apr 11, 2021 at 21:40
  • 8
    Turning the heater to max (and fan to minimum) also activates additional electric cooling pumps on some cars, which aid in pushing water though the heater core when refilling / bleeding the cooling system.
    – towe
    Apr 12, 2021 at 10:03
  • 2
    Interesting. My '97 Jeep Wrangler always has hot engine coolant running through the heater core, and the only control is to direct the cabin air through it or not. So in the heat of summer with the A/C on full blast, the heater core is just sitting there hot with very little airflow.
    – AaronD
    Apr 12, 2021 at 21:22
  • 1
    If you have an anti-theft feature on your radio, the radio becomes locked when the battery is unhooked. That way if it is stolen it will not function. There is a specific code that must be entered to enable it again. Usually the presets are kept on these types of radios. But you probably have a radio without this anti-theft feature. So when the mechanic unhooks the battery, all presets are lost. A good mechanic will disconnect the battery when working in or around a cars electrical system. Either that or the mechanic likes to listen to different channels. JK
    – Jupiter
    Apr 13, 2021 at 2:02

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