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sean View Drop Down
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    Posted: 07 June 2007 at 6:17pm
These are not "genuine Willys" parts, but are vintage period service parts, representative of the type used in CJ2A.

These are old school bellows type thermostats.  The bellows is filled with some kind of liquid or gas (still unknown for sure) that expands w/temperature, opening the thermostat valve.

From left to right:
  • Harrison #1251 - 160º "High temperature", 1946 vintage, fits "Willys Jeep (military & civilian)".
  • Fulton #30-FHT - 155º "High temperature", fits "Willys and Jeep - ALL TRUCKS".
  • Harrison #312285 - 180º "Extra high temperature", 1950 vintage, fits "Willys 1937-1950 ALL".
       

Modern thermostats are a wax-pellet type.  A wax pellet is contained w/in a copper slug, operating against a fixed rod, much like a hydraulic cylinder.  The thermostat valve is fixed to the slug. When the wax expands w/temperature, the slug pulls the valve open.  At cold temps, the valve is forced closed by the external spring.

There are technical differences between the two types that may be worth considering. YMMV.

1) Valve opening size.  Both types use a circular valve, which when open creates a cylindrical passage.
  • The wax pellet valve is 1" diameter, and opens to .3", producing an area of .94 sq-in for coolant passage.
  • The bellows units are 1.375" diameter, and open to .4", producing an area of 1.73 sq-in for coolant passage.
       

Which one allows more coolant to flow through the radiator?  Specially at the relatively low operating pressure (4 PSI) of the L-head, compared to the higher pressures (10-15 PSI) in cars that modern thermostats are designed for.

In lieu of the bellows type, it might be worth trying to find a modern type w/large valve, which has about the same passage area as a bellows:

       

2) Exposure to coolant.  The L-head thermostat housing was designed for a bellows thermostat.
  • The bottom of a bellows unit is about even w/the top of the head.  Coolant won't have to expand much to reach it.
  • A wax pellet sensor slug sits much higher within the housing.  Coolant has to reach a higher level for the thermostat to begin working.
   

3) Failure mode.  While both types are quite reliable, if they do fail ......
  • When a bellows type fails, it opens, allowing coolant to circulate.
  • When a wax pellet type fails, it REMAINS CLOSED! Shocked
Which would you rather have?

Sean

Edited by sean - 28 Dec. 2010 at 9:56am
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Brachus12 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Brachus12 Quote  Post ReplyReply Direct Link To This Post Posted: 22 Oct. 2008 at 10:46am
Here's another Harrison that I picked up off eBay.



Harrison #3122283 - 160deg, 1950 vintage, fits "Willys 1937-1950 ALL".
47 CJ2A #101361 "Bugger"
42 GPW 75248
SPEN Trailer
62 M170 13758

http://s4.photobucket.com/albums/y119/brachus/Willys
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Post Options Post Options   Thanks (0) Thanks(0)   Quote willys54wagon Quote  Post ReplyReply Direct Link To This Post Posted: 03 Aug. 2011 at 3:48pm
Gents,
 
I have the 3 bolt thermostat housing which is designed for the bellows thermostat.   Bubba used a tin can to hold the thermostat up to the top of the housing.   Seemed to have worked but wondered what others are using for the spaceer.
 
What would be the names for items 8, 9, 10?   9 obviously being the housing , 8 thermostat and 10?
 
 
 
Notes above refer to a disadvantage of the thermostat being up in the housing and that the new ones fail closed.  Is it possible a spring was used to keep the new style thermostat in place and provide a release if it failed closed?
 
A final note that NAPA does not carry a gasket for this but sells gasket material to cut your own.  Not a big deal, just interesting.
Two jeeps on the road, one is close and the rest are dreams.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote willys54wagon Quote  Post ReplyReply Direct Link To This Post Posted: 03 Aug. 2011 at 3:55pm
Is this the part I am looking for to fit in the housing to hold the thermostat up?
http://www.autopartswarehouse.com/details/QQJeepQQWillysQQOmixQQThermostat_HousingQQ19461956QQO321710701.html
 
If so looks like it would work to place the thermostate closer to block or up in the housing.  Is one better than the other?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote willys54wagon Quote  Post ReplyReply Direct Link To This Post Posted: 03 Aug. 2011 at 3:57pm
Ok, now I see it at Walcks for $5.20 a much cheaper price.
http://walcks4wd.com/catalogsearch/result/?q=thermostat
Two jeeps on the road, one is close and the rest are dreams.
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