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.


1 Answer 1


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.

  • That's brilliant! Wonder if you could get a submersible endoscope that would let you do it without needing to drain the coolant?
    – dlu
    Commented Jan 13, 2017 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. Commented Jan 13, 2017 at 7:29

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