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Is there a way to reasonably diagnose a water pump failure directly? In How to test the function of a water pump? the question is posed but the accepted answer only provides a way to infer that the pump is functioning:

Typically [with impeller failure], 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.

A couple of questions have come up:

where it would be nice to have a way to confirm that the pump is working (at least in a qualitative way) without having to spill a lot of coolant or pull the pump.

Would it work, for example to:

  • Squeeze one of the heater or radiator hoses and listen and/or feel for coolant movement (like kinking a garden hose to cut off water flow), or
  • Listen with a stethoscope or screwdriver at a constriction or perhaps at a tee for the sound of rushing fluid – perhaps while adjusting engine speed.

It seems like if either of those methods would work they would make it possible to detect flow and decide if the pump was suspect.

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What I did to diagnose a problem with the water pump on my 98 Mazda 626 was to drain the coolant, remove the thermostat and use a cheap PC based endoscope I got off Amazon to visualize the water pump impeller. I disconnected the fuel pump and relived fuel pressure, inserted the endoscope via the thermostat housing until I could see the impeller, then while taking a video, cranked the engine a few times to make sure I could see the entire impeller and see how it was moving:

enter image description here

What I saw when reviewing the video was that all the impeller fins had disappeared! This was verified when I removed the pump:

enter image description here

I found on of the fins in the bottom of the water pump as can be seen in the picture. I also found another fin jammed into the water intake passage so firmly that I had to remove it with needle nose pliers:

enter image description here

I have a strong feeling that whatever is left of the rest of the fins are probably jammed deep down in the water passages somewhere.

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  • That's brilliant! Wonder if you could get a submersible endoscope that would let you do it without needing to drain the coolant?
    – dlu
    Jan 13 '17 at 5:29
  • @dlu Don't know if it's be worthwhile as you will likely still need to remove the thermostat which will entail at least partially draining the coolant.
    – Robert S. Barnes
    Jan 13 '17 at 7:29

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