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> Fixing my thermostat, How I did it
MrKona
post Apr 23 2008, 11:07 PM
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There was a recent thread about thermostats... it reminded me that the thermostat that came with the engine I'm building was broken, and I had to either buy a new, used one, or see if I could fix the one I have. I followed the informative article by Richard Atwell with good results. Ratwell link

My thermostat had sprung a leak somewhere which eliminated the negative pressure vacuum a functioning thermostat holds at room temperature. The thermostat is supposed to measure around 35mm in length at room temp, mine measured around 46mm, which is the normal expanded state length. I examined it closely and could not find any cracks around the perimeter, so I assumed there must be a break at a brazed surface. I was in luck, it was fixable!

Just for kicks, I placed it in a hot water bath approximately 180 degree F, and there was no significant change in length, pre- to post-bath.


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MrKona
post Apr 23 2008, 11:13 PM
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First step was to remove the top on the side with the small threaded area where the thermostat cable attaches. I held the thermostat gently with my table vise and applied heat to melt the solder holding the top on. Came of easily...

I then cleaned up the contact surfaces with a wire brush on a Dremel tool.

In addition, I also removed the bit of solder and a small ball bearing from the small hole at the middle of the threaded area on the top.


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MrKona
post Apr 23 2008, 11:17 PM
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While I had the top off, I blew out any debris with a little air. I then fluxed the rim, mounted the thermostat gently back in the vise and brazed the lid back on. (No picture of that one, but you can imagine...). I left the small hole in the lid open.

Next step was to compress the thermostat down and wrap it in metal wire to keep it compressed.


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MrKona
post Apr 23 2008, 11:23 PM
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Next step was to inject approximately 2ml of 99% Isopropyl alcohol. 99% alcohol has a boiling point of 82C, around 180 degrees F. I drove around to three different places looking for 99% alcohol but couldn't find it. The best I could do was 91%, which has a boiling point of around 177 - 180 degree F, depending what MSDS you look at. Close enough for me as I was having no luck finding 99%.

I work for a medical device company, so luckily had a 3ml syringe handy...



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ericread
post Apr 23 2008, 11:23 PM
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(IMG:style_emoticons/default/popcorn[1].gif)
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MrKona
post Apr 23 2008, 11:28 PM
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With the alcohol now injected through the small hole, it was time to seal the hole and trap the alcohol inside! A little bit of careful heating and solder did the trick. Heat carefully, as you don't want to melt the solder around the edges. My final result may not look pretty, but it held vacuum! The thermostat was now right around 35mm with the wire removed. Right at spec! (IMG:style_emoticons/default/piratenanner.gif)


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MrKona
post Apr 23 2008, 11:32 PM
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And now for the water test.

At 140F, the thermostat still measured right around 35mm.



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MrKona
post Apr 23 2008, 11:33 PM
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Looks like it started opening a little early... At temp of 165F, it was now up to spec at 46mm. (IMG:style_emoticons/default/dry.gif)


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MrKona
post Apr 23 2008, 11:36 PM
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... and at 184F, it had opened up to around 55mm, it's maximum length.

In conclusion, the thermostat opened up at a little lower temp than spec, but I'll take it. I just saved myself $100 not having to find a new one!


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ericread
post Apr 23 2008, 11:51 PM
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So what you are saying is that between "Rare Beef" and "Poultry" the expansion was within acceptable parameters (IMG:style_emoticons/default/av-943.gif)

Seriously, excellent post! (IMG:style_emoticons/default/aktion035.gif)
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MrKona
post Apr 24 2008, 01:15 AM
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QUOTE(ericread @ Apr 23 2008, 10:51 PM) *

So what you are saying is that between "Rare Beef" and "Poultry" the expansion was within acceptable parameters (IMG:style_emoticons/default/av-943.gif)

Seriously, excellent post! (IMG:style_emoticons/default/aktion035.gif)


It took me a few minutes to get that joke... (IMG:style_emoticons/default/biggrin.gif) (IMG:style_emoticons/default/av-943.gif)
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purple
post Apr 24 2008, 10:23 AM
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Classic thread?
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dbgriffith75
post Apr 24 2008, 10:51 AM
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That's a really good suggestion- I didn't know it was possible to actually fix it. The thought crossed my mind but I didn't realize you could actually take it apart and be able to put it back together without totally f***ing something up.

I'll try this if it turns out mine's actually bad. Thanks!
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jim_hoyland
post Apr 24 2008, 10:52 AM
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QUOTE(purple @ Apr 24 2008, 09:23 AM) *

Classic thread?


Definately ! Very nice write up.
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Steve Thacker
post Apr 25 2008, 11:47 AM
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UMMMPH Yea Baby Yea ! UMMMPH
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Bryan,
Excellent post! You one smart coolie. (IMG:style_emoticons/default/aktion035.gif)
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