Printable Version of Topic

Posted by: MrKona Apr 23 2008, 11:07 PM

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. http://www.ratwell.com/technical/Thermostats.html

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.


Attached image(s)

Posted by: MrKona Apr 23 2008, 11:13 PM

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.


Attached image(s)

Posted by: MrKona Apr 23 2008, 11:17 PM

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.


Attached image(s)

Posted by: MrKona Apr 23 2008, 11:23 PM

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...




Attached image(s)

Posted by: ericread Apr 23 2008, 11:23 PM

Posted by: MrKona Apr 23 2008, 11:28 PM

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!


Attached image(s)

Posted by: MrKona Apr 23 2008, 11:32 PM

And now for the water test.

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




Attached image(s)

Posted by: MrKona Apr 23 2008, 11:33 PM

Looks like it started opening a little early... At temp of 165F, it was now up to spec at 46mm.


Attached image(s)

Posted by: MrKona Apr 23 2008, 11:36 PM

... 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!


Attached image(s)

Posted by: ericread Apr 23 2008, 11:51 PM

So what you are saying is that between "Rare Beef" and "Poultry" the expansion was within acceptable parameters

Seriously, excellent post!

Posted by: MrKona Apr 24 2008, 01:15 AM

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

Seriously, excellent post!

Posted by: purple Apr 24 2008, 10:23 AM

Classic thread?

Posted by: dbgriffith75 Apr 24 2008, 10:51 AM

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!

Posted by: jim_hoyland Apr 24 2008, 10:52 AM

QUOTE(purple @ Apr 24 2008, 09:23 AM)

Posted by: Steve Thacker Apr 25 2008, 11:47 AM

Bryan,
Excellent post! You one smart coolie.