Please help me diagnose this noise...

[inAjet]

Hi All,

I've started noticing a strange noise coming from my 4.3L Merc that at first sounded like grinding but, when listening more closely, actually almost sounds more like gurgling. It seems to be coming from the thermostat housing, so I'm wondering if this is the normal noise of water flow as the thermostat modulates and I've just never noticed it?

Please have a listen to the attached video (link) and let me know what y'all think! I'd appreciate any thoughts...

Cheers,

Chris
Vancouver, BC

 

[Rick Stephens]

Crappy water pump?

Might pull the belts and fire up for a couple minutes. See if the noise goes away.

 

[inAjet]

Thanks for the tip, Rick. New water pump was installed at the end of last season. I'll give your suggestion of pulling the belt a try.

 

[inAjet]

So I pulled the thermostat cover to see what was going on inside, and everything appeared normal. I spun the circulation pump by hand to see what it felt like; it rotated smoothly and freely but made a bit of noise, although nothing I thought was outrageous:

https://www.dropbox.com/s/tf67phigibe0sdz/IMG_0833.MOV?dl=0

Then I briefly started the motor to check the water flow from the impeller on muffs. The first link below was at around 1000 RPM, and the second at 1500 RPM. There's definitely water flowing, although at higher RPM it seems to pulse a bit. I've never looked at it before, so I don't know what's normal.

https://www.dropbox.com/s/fof09oy4au9u7d1/IMG_0834.MOV?dl=0
https://www.dropbox.com/s/p3twi7mwycweba8/IMG_0837.MOV?dl=0

Can anyone comment on whether the above is all normal?

 

[inAjet]

Turns out the culprit was the circulation pump. Put a new one on today, and new thermostat while at it, and she's running smooth and noise-free once again!

 

[Rick Stephens]

Yah. Sorry I missed the video of you spinning the pump by hand. Noisy little bugger. Glad you got it!

Rick