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Thread: Bad thermostat photos

  1. #1
    ishoottrap's Avatar
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    Bad thermostat photos - with cross sectioned photos

    That is, photos of the bad thermostat I pulled out of my '05 last Sunday. Not stuck fully open but really stuck, can't budge it with hot/cold bath or as hard as I can force it with my fingers. Sure looks like the material of the heat motor body is incompatible with something in the coolant as it's pretty rough and cruddy looking. The rest of the body/springs look practically new.

    BTW, somone was asking about orientation. You can see the offset in the stamping in the second photo. The orientation of the photo is the orientation of the 'stat in the bike, bleed hole to the top.

    If I get really ambitious, I might dissect it to have a look at the innards:







    I have the full res photos if anyone is interested in a really close look.

    -Scot


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  2. #2
    Moderator Byron's Avatar
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    Re: Bad thermostat photos

    Maybe you've brought to light what might be happening with these. If the outside surface is rough for whatever reason I wonder if the inside is doing the same thing and maybe that is why it is frozen on the shaft?

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    ------------Jeff------------ Dinkie Diesel's Avatar
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    Re: Bad thermostat photos

    Did you shoot these photos with that lens you had in your old avatar? Depth of field = .67" Good Job!!!

    I still wonder about the reason for failure. Your thermostat is clean except for that bit of corrosion on the outside of the heat motor. And, being locked up as you say it is makes me think the tolerance of the shaft and whatever it slides in is improper or that it where some corroding is taking place. If you have the means to dissect it, please do. Thanks for posting.

    Jeff
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    Re: Bad thermostat photos

    Quote Originally Posted by Dinkie Diesel View Post
    Did you shoot these photos with that lens you had in your old avatar? Depth of field = .67" Good Job!!!

    Jeff
    Yeah, it's a bugger to hold but it does a nice job.... Actually, I used the venerable Nikkor Micro 105 and had to go to f11 to get the DOF I got! It's a sharp lens and the natural res. of these photos is around 4200 x 2800, lots of detail....

    I haven't decided how to dissect yet, I have some pretty thin wheels for my die grinder, perhaps up each side of the heat motor, I also have a pretty thin blade for my mill slitting saw but holding this thing tightly enough to use the mill without crushing it might be a problem. Heck, maybe even a jeweler's saw would do the trick.

    -Scot

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    The innards

    Ok, I had a little time so I did it. First few shots are with the housing off. At this point, I wasn't sure what moved but the stuff on the small shaft where it enters the housing doesn't look good:









    Here it is with the housing cross sectioned. The slots in the two steel shafts at either end and the black disc in the middle are from cutting the housing. The wax plug is the red/black stuff in the large portion of the housing, the black disc in the middle is a rubber diaphragm that fits in the recess in the left end of the housing between the wax and the base of the extension which is the cross sectioned piece on the left. The two small circular pieces between the extension halves appear to be a piston and seal that ride in the bore of the extension. I'm not sure exactly how they go in but I'm betting cup side of the small rubber piston facing the diaphragm and the metal disc between the piston and actuating rod which is the piece furthest to the left:



    Here's a tighter shot of the extension, piston and actuating rod:



    And the piston:



    And finally the hosing with the wax plug:



    Since the wax appears to be complete and I could detect no sign of loss of integrity of the crimps, plugs, diaphragm or piston seal, I think the culprit is the buildup on the actuating rod causing it to stick tightly in the extension. The fact that there is no buildup on the portion of the rod outside the extension suggests that this is a interaction between the brass, steel and coolant causing deposits of some form to build up on the actuating rod and in the bore of the extension to the point that the return spring can no longer force the actuating rod back into the housing. The fact that some folks report their thermostat working once they put it in a hot bath suggests that the brass extension is expanding enough to open the bore and release the actuating rod.

    I think next steps in an investigation would be to compare the buildup on thermostats that have been run for a significant period with coolant other than the initial fill. Still seems like an materials compatibility issue to me.

    -Scot

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    Site Supporter azlife4me's Avatar
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    Re: Bad thermostat photos

    Scot,
    Great photos. Thanks for taking the time to do that.
    Tom
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    Re: Bad thermostat photos

    Nice video of making a thermostat. The one in the video is a single valve but the principal is the same.

    http://www.youtube.com/embed/xVPtIi6sVYg

    -Scot

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    ------------Jeff------------ Dinkie Diesel's Avatar
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    Re: Bad thermostat photos

    Yeah, I'll say! Thanks for doing that! Now I believe some/all of this problem could be alleviated with the proper choice of materials to manufacture the T-stat. Do you have an electron microscope? We could check the molecular composition. Your pictures look like the shaft is galling. That could be a combination of fit and/or materials. I think this also eshews the idea of the contaminants (radiator paint) causing the problem, maybe not.

    Good work!

  9. #9
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    Re: Bad thermostat photos

    Quote Originally Posted by Dinkie Diesel View Post
    Your pictures look like the shaft is galling. That could be a combination of fit and/or materials. I think this also eshews the idea of the contaminants (radiator paint) causing the problem, maybe not.

    Good work!
    I saved the parts in case I do get access to a lab. Had one at my last job but this one, not so much. The wipe on the small actuating rod looks like something is building up on the shaft and then being wiped by the brass extension. I'm assuming the shaft is stainless, it would be nice to know what material is building up. Since the outside of the brass housing is so discolored/rough, I have to believe something is attacking the brass and perhaps once it goes into solution, it plates onto the actuator shaft because it's in such close vicinity. Wonder what's in that neon-green thick stuff that passes for OEM coolant?

    -Scot

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    Dan Mulkiewicz dmulk's Avatar
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    Re: Bad thermostat photos

    Is that corrosion on the shaft actually paint build up from inside the radiator?
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