 Thermostat Question, How does it work? |
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| pbanders |
 May 4 2022, 09:16 AM
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#1
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Senior Member  Group: Members Posts: 943 Joined: 11-June 03 From: Phoenix, AZ Member No.: 805  |
While I may have done a transistor-by-transistor analysis of the ECU and used pSpice to simulate the injector driver circuit, I've never done squat with my thermostat system. Basically, it works, so I leave it alone.
But I'm curious, how do the bellows work? When the car is hot, the bellows expand, and the cable tension is released. Is there an internal spring? Something about wax? Help me out here, thanks. |
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Replies(1 - 9)
| mrholland2 |
May 4 2022, 09:17 AM
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#2
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Senior Member Group: Members Posts: 761 Joined: 7-September 11 From: Santa Maria,CA Member No.: 13,531 Region Association: Central California |
QUOTE(pbanders @ May 4 2022, 08:16 AM)  While I may have done a transistor-by-transistor analysis of the ECU and used pSpice to simulate the injector driver circuit, I've never done squat with my thermostat system. Basically, it works, so I leave it alone. But I'm curious, how do the bellows work? When the car is hot, the bellows expand, and the cable tension is released. Is there an internal spring? Something about wax? Help me out here, thanks. I think there is a spring on the flap shaft that pulls against the thermostat. |
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| Mark Henry |
May 4 2022, 09:35 AM
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#3
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that's what I do! Group: Members Posts: 20,065 Joined: 27-December 02 From: Port Hope, Ontario Member No.: 26 Region Association: Canada |
QUOTE(mrholland2 @ May 4 2022, 11:17 AM) QUOTE(pbanders @ May 4 2022, 08:16 AM) While I may have done a transistor-by-transistor analysis of the ECU and used pSpice to simulate the injector driver circuit, I've never done squat with my thermostat system. Basically, it works, so I leave it alone. But I'm curious, how do the bellows work? When the car is hot, the bellows expand, and the cable tension is released. Is there an internal spring? Something about wax? Help me out here, thanks. I think there is a spring on the flap shaft that pulls against the thermostat. Close, the spring on the flaps opens the flaps and provides tension for the cable, as the bellows expands/contracts it lets the flaps move. If your T-stat bellows is always expanded then she be fuched. |
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| 914werke |
May 4 2022, 10:08 AM
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#4
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"I got blisters on me fingers" Group: Members Posts: 11,248 Joined: 22-March 03 From: USofA Member No.: 453 Region Association: Pacific Northwest 
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Brad are you are asking what is contained inside the unit that causes the bellows expansion?
I believe it is a wax that liquefies when up to temp? |
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| mepstein |
May 4 2022, 10:21 AM
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#5
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914-6 GT in waiting Group: Members Posts: 19,875 Joined: 19-September 09 From: Landenberg, PA/Wilmington, DE Member No.: 10,825 Region Association: MidAtlantic Region
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Always test it inside the bracket or it will over expand.
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| emerygt350 |
May 4 2022, 11:42 AM
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#6
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Advanced Member Group: Members Posts: 2,882 Joined: 20-July 21 From: Upstate, NY Member No.: 25,740 Region Association: North East States |
I ripped my old one apart pulling it out of the car, I think it is a bimetal design perhaps? There was no 'wax' inside the bellows. Or perhaps I let all the magic smoke out when I ripped it open with my pliers.... Seemed more like a metal expansion contraction type device. Not a spring inside though, unless it is contained within the bellow portion. I think. I was kind of pissed at it for how stuck it was.
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| pbanders |
May 4 2022, 12:43 PM
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#7
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Senior Member Group: Members Posts: 943 Joined: 11-June 03 From: Phoenix, AZ Member No.: 805 |
Here's a 914 thermostat in operation:
https://www.youtube.com/watch?v=WFrcKSB-oUM From what I can tell, it's a metal bellows filled with wax, which expands when heated and contracts when cooled. Old tech, but it works. |
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| barefoot |
May 4 2022, 01:19 PM
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#8
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Senior Member Group: Members Posts: 1,370 Joined: 19-March 13 From: Charleston SC Member No.: 15,673 Region Association: South East States
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This may help:
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| iankarr |
May 4 2022, 02:00 PM
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#9
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The wrencher formerly known as Cuddy_K Group: Members Posts: 2,556 Joined: 22-May 15 From: Heber City, UT Member No.: 18,749 Region Association: Intermountain Region
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I believe there’s a liquid (alcohol?) sealed inside the bellows and heat causes it to turn into a vapor and expand…
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| pbanders |
May 19 2022, 11:08 AM
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#10
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Senior Member Group: Members Posts: 943 Joined: 11-June 03 From: Phoenix, AZ Member No.: 805 |
Ian Karr is correct, the working fluid is alcohol. Richard Atwell has an excellent page on the details of the thermostat, with all the info you'll ever need.
https://ratwell.com/technical/Thermostats.html Oh, and I received my new thermostat from Awesome Powdercoat, a very nicely made component. As my existing thermostat seems to be working fine, this new one will go into my spares cabinet - which is getting fuller all the time. |
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