Today, I came across this article while surfing through Gates website: https://www.gatestechzone.com/en/news/2017-06-water-pump-replacement It mentions some points about installing a new water pump. The 5th one says: A lot of mechanics stick to the following procedure: replace the water pump, tighten the bolts, install the belt, tighten the tensioner, refill the cooling system … and start the engine (or just rev it up). But coolant takes a little time to get everywhere it’s supposed to be, so the water pump runs dry for a few seconds. This ruins the seal and heightens the risk of premature leaks or a noisy water pump. Instead we’d advise you to ease the car down after you’ve installed a new water pump, refill the cooling system, lift the car back up and manually rotate the pump about ten times, all the while making sure it rotates freely. Due to this rotating movement, coolant gets sucked into the mechanical seal component, effectively creating a film, which keeps coolant from spilling out.
I don't understand this paragraph. It says the pump runs dry for a few seconds. How is this possible? Isn't the pump immersed in coolant when you refill and bleed the system? Why should we rotate it manually?

1 Answer 1


Because the coolant does not get fully circulated around the shaft / seals of a pump and seals get damaged when they run dry.

So rotating the pump lubricates the seals and doing that at low rpm is better than engine speed or 2* engine speed depending on pulley ratios.

  • Great answer! So, could we just install the new pump, fill the system and rotate pump shaft by hand before installing the belt? (Without having to rotate the engine by crank pulley with the belt on)
    – LFY MP7.3
    Commented Jul 8, 2021 at 17:23
  • 1
    “at low rpm” means low rpm like by hand
    – Solar Mike
    Commented Jul 8, 2021 at 17:33

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