Bad thermostat photos

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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
 

Byron

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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? :confused:
 

Dinkie Diesel

------------Jeff------------
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Did you shoot these photos with that lens you had in your old avatar? :rofl1: Depth of field = .67" :D 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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ishoottrap
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Did you shoot these photos with that lens you had in your old avatar? :rofl1: Depth of field = .67" :D 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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ishoottrap
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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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ishoottrap
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Nice video of making a thermostat. The one in the video is a single valve but the principal is the same.

[video]http://www.youtube.com/embed/xVPtIi6sVYg[/video]

-Scot
 

Dinkie Diesel

------------Jeff------------
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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? :D 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!
 
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ishoottrap
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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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I have had a similar build up on the shaft of an ST11 thermostat. It may have been in the bike a long time. Hitting with a hammer freed it up, and it seemed to work when tested in water, but I just kept it out of interest.
 
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ishoottrap
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Another one

Thanks to Krivanj for sending me his thermostat. I disected this one with a little more finesse:

Stuck open:


Here are some shots of the actuating rod near the housing:






Removing the extension that houses the actuating rod, we see the rubber diaphragm in the heat motor body covering the thermal wax:


Under the rubber diaphragm is the wax pellet, looks like no leakage here. The scratches at 7:00 are from me picking off the diaphragm:


And the other end of the heat motor, sealed with a plug and no leakage here either:


Now, examining the extension we see a soft black substance located just over the diaphragm and under the piston seal:


Here is that black substance removed in as close to 1 piece as I could remove it:


After removing the black substance, I tapped the actuating rod, piston and seal out with a drift punch, here is the respective position of all the parts. This thermostat has a few more pieces than the one I referenced previously (located on YouTube). Rather than the actuator extending down into the wax pellet of the heat motor, this thermostat relies on the soft black material to transfer force from the expanding pellet and diaphragm to the seal/piston and finally the actuating rod.:


A close look at the seal:


and the piston:


and finally the actuating rod:


Both the piston and actuating rod show definite signs of the soft black substance having leaked past the seal. My hypothesis is that the soft black material used as a hydraulic link between the diaphragm and the actuating rod seal leaks past the seal and piston and onto the rod where it interacts with the coolant and causes the actuating rod to stick in the housing extension.

I'll dissect the others as they come in, I have Bakerboy's "good" OEM thermostat and will dissect it as well. I tried to remove the actuating rod in this thermostat by clamping it in a vise and pulling by hand the heat motor/extension, it wouldn't budge. I could get it to twist a bit but it was really stuck.

-Scot
 

Mellow

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Great pictures, thanks for all the effort.
 
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ishoottrap
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Great pictures, thanks for all the effort.
Thanks, have to put that used micro-Nikkor lens to use :). It's such a pervasive and simple device, the fact that there is such a high failure rate of this model certainly points to the non-standard. I suspect that the "black goo" that is not in most thermostat designs is the culprit. Actually when it escapes where it should be and makes it's way to the extension where the actuating rod lives, that's the problem.

I have no contacts at Honda and in fact, the dealership where I bought the bike is now belly up so no-one local to deal with. If anyone here has a contact and interest, I'd be happy to help supply data.

-Scot
 
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ishoottrap
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TT thermostat construction

Anyone know if the Turbo Tom stat has that black material?

Raymond
I don't think so, notice how much bigger the section which contains the actuating rod is on the TT thermostats than on the OEM in this photo by Bakerboy:



I think it's constructed more classically like this:



Here's a good video showing how thermostats are made (great cutaway image at 2:48):

http://www.youtube.com/watch?v=xVPtIi6sVYg

The diaphragm in the classical thermostats separates the wax pellet from the actuating rod and acts on the actuating rod directly. This requires enough volume for the diaphragm to flex as well as contain the actuating rod. The Honda OEM employs a very narrow, small volume housing for the actuating rod which does not have enough room for the diaphragm. The small volume containing the black "goo" just over the diaphragm acts to change the volume increase of the wax pellet into the same volume increase but a much smaller bore so the linear motion is much greater. The small housing potentially allows somewhat better flow characteristics depending upon housing shape.

-Scot
 

Mellow

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Here's a pic of my Good OEM thermostat after 55,000 miles and just over 3 years. I was planning a coolant change and had a TurboTom T-stat sitting around so I figured if I didn't change it, THEN I'd end up with a sticking one.

Well, my fluid was great looking, NO PARTICLES AT ALL suspended in the fluid.. There was also NO PAINT OVER SPRAY on the radiator parts. It could be Honda changed their production at some point to reduce/eliminate these types of failures.

My bike has never had an issue getting to 3 bars and the OEM thermostat still moves with ease. You can see some VERY light build up on this one but no where near as bad as some of the others in this thread. Also, please keep in mind this is my FIRST COOLANT flush... so, I'm overdue by a year.

 
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