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4. Don’t use coolant that’s old or too cold Collecting the coolant from your old water pump and reusing it may seem like a sensible (and economical) thing to do, but we strongly advise against it. After all, coolant tends to deteriorate: it has an expiry date. Refill the cooling system with new coolant and make sure … • … to use the kind recommended by the vehicle manufacturer (don’t start mixing coolants either, because they might counteract each other). • … to get the proportions right. If you add too little antifreeze, your cooling system is more likely to freeze, but adding too much might also be harmful. We recommend a fifty-fifty mix of water and antifreeze (make that 65% antifreeze and 35% water for Alpine-cold or Siberian climates). • … to mix in warm water with your antifreeze – as odd as that may sound. Adding cold coolant to a heated engine can cause thermal shock and damage the seal, even in a new water pump. • … to use distilled, deionized or even bottled water, but never tap water. Regular tap water can be very hard, leaving mineral deposits inside the radiator, heater core and engine block. When these deposits break off, they can damage the water pump seal.
5. Do rotate the pump manually 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.
6. Don’t worry about seepage from the weep hole Every mechanically driven water pump has a weep hole that might leak a little in the beginning. Some seepage from the weep hole is completely normal with a new water pump: a mechanical seal has a break-in period of about ten minutes (meaning that it takes about ten minutes of operation for the seal to properly seal itself). However, if you still see seepage a few days after you’ve replaced the pump, or if you notice more pronounced seepage or even drips from the weep hole, you do have a problem: these symptoms point to a faulty installation.
7. Do properly vent the cooling system When you’re done replacing a water pump, it’s good practice to burp the cooling system to get rid of all the trapped air. Some thermostats have a small hole at 12 o’clock, and a jiggle pin which allows the air to escape (while preventing new air from getting in).