Is it possible to test a water pump for proper function (ability to move a certain volume of coolant) without disconnecting it from the engine? If so, how would one do that?

1 Answer 1


I've been wondering this too as a lot of overheating related questions come up.

There are 2 ways water pumps fail - leaks and impeller failure. Leaks can typically be seen, so they are easier to diagnose. Impeller failure is difficult to detect.

Typically, the engine will overheat, but the heater core and radiator will still be cold. With a thermostat failure, the radiator will be cold, but the heater core should still get hot. This leads to a possible false positive if the heater core is plugged and the thermostat failed.

  • 1
    I've only seen impeller failure on VWs with the plastic impeller. 99% of water pumps I see are metal impellers and failure is either leaking or bearing failure.
    – Ben
    Mar 18, 2016 at 21:19
  • 2
    @ben Steel impellers can rust away if there is no corrosion inhibitor in the coolant, I.e. Just water has been used as coolant.
    – HandyHowie
    Mar 19, 2016 at 10:04
  • @Ben I had a plastic impeller on my 95 dodge spirit. It had the 6G72, which is used in many dodge and Mitsubishi applications. Not sure if it was original. The replacement was metal.
    – rpmerf
    Mar 23, 2016 at 15:53
  • So if the engine is overheating, and I see that the heater doesn't work, I can reasonably conclude that the water pump is the source of the problem? Mar 28, 2016 at 10:29
  • First, you need to make sure there isn't a clog, plugged heater core, or bad heater core valve. Flush it to ensure water can flow through the heater core. Once your sure there isn't a clog, it's overheating and you don't get heat, then Yes, I would assume it's the water pump.
    – rpmerf
    Mar 28, 2016 at 10:44

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