Some engines nowadays have a switchable water pump that can be turn off at cold start, like the ones found on some Volkswagen diesel engines. Those a mechanical pump that can be disabled at cold start in order to shorten warming up time. At least, that is the marketing claim. Those engine still have a regular thermostat.

Any idea, if those pumps really make a difference concerning warming up time ?

  • 1
    They will make a difference for sure when they fail to kick in...
    – Solar Mike
    Apr 3, 2020 at 17:33
  • exactly! that's why I'm wondering if the benefits outweigh the cons. Apr 3, 2020 at 18:52
  • The pump circulates the coolant throughout the system whether cold (internal to the engine) or hot (through the entire system), with a little help from the thermostat. The engine gets hot at certain spots within the engine sooner than others. If you are circulating the coolant when the engine is cold, I would think you'd run the risk of overheating in these locations. The risk warpage due to uneven heating would seem to me to be quite a real scenario without the coolant pump running. I'm not sure what it would really gain you? Apr 3, 2020 at 19:54
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    @Pᴀᴜʟsᴛᴇʀ2 the gain? well, that IS the theme of this post. you can look at pics3.tdiclub.com/data/517/820433_EA288.pdf as an example. to avoid hot spot, the engine head has its own cooling circuit and pump. only the block is switched off. Apr 3, 2020 at 21:28
  • 1
    So it really doesn't turn off. Seems like something more to break and be replaced. Why mess with something which works. Apr 3, 2020 at 21:31


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