New Mexican T1 Thermostat and Failsafe

[MGVWfan]

I just installed one of the "new" T1 thermostats on my '73 412, the one with the big honking spring around the element. Due to its construction, it is not entirely fail-safe, as someone else pointed out on the forum in another post. It's built like a water-cooled thermostat, with a wax pellet in a brass chamber that expands (greatly in this case, some 3/4" or 19mm) when the target temp is reached, pushing on the brass pushrod through a flexible diaphragm. The big spring compresses the thermostat as it cools, and that's the part that's not fail-safe. If the diaphragm leaks all the wax out, or the pushrod jams in its bushing, the spring keeps the whole thing in the "cold" (compressed) state.

Since the NOS bellows-style (Wahler) tstats are getting scarce, and come with pinhole corrosion (I had 3 over the last 2 years all die the same way, pinhole leaks due to corrosion in the belllows), I think it behooves us to figure out a way to use the spring-style T1 tstat, including a fail-safe. I think I've got a simple way to disconnect the cable when a certain temperature is reached, and I need some collective wisdom to come up with a good fail-safe release temperature.

By connecting the cable to a small brass tag, and the tstat to another small brass tag, the two SOLDERED TOGETHER previously, when the solder's melting point is reached, the two tags part ways, the cable releases, and the flaps go to full open. Electronic solder is available with melting points from 361 deg F/181 deg C (63/37 Sn/Pb) to 428 deg F/220 deg C (Sn/Ag/Cu), and of course there are other alloys for plumbing and other uses with higher and lower melting points. The question is, what is a good fail-safe release temperature, keeping in mind that the tstat "sees" air from the #1-2 cylinder barrels predominantly, not really from the heads, and the heads are the most sensitive to overheating. So, even if the heads can run at, say, 350 deg F OK, does that mean we want the "fail safe" temp as sensed at the thermostat location to be say 360 deg F? Comments please...

[raygreenwood]

I have one of those thermostats I need to send back to a person who let me borrow one....in summer .
I tested it a bit....I'm just not thrilled with the whole design for use udner a hot engine 5" off the road in the "dust and dirt stream".
I hope to have some of that actuator wire in my hands in a couple weeks.
I devised a plate design that bolts onto the two holes on the block where the original bellows bracket was.

What I am having to devise is a "zigzag" pattern between a sereis of pins so I can get the required length of actuator wire to fit within a small space. Since this wire works exactly opposite the bellows (remember the bellows expands as it warms up letting the cable play out and releasing the flaps....wheras this wire contracts when heated).....it will be pulling a short lever on a pivot bolt....that is attached to the wire. The pivot will actually be pulled back by a spring....which keeps the flaps closed when cold....just like normal. When the actuator wire heats up...it shortens and pulls the lever opposite teh spring to allow the flaps to open. With enough of a length of actuator wire...it will have many times the pull of the spring that holds the flaps closed.

The actuator wire is reliable for millions of cycles. If it fails though...I have been thinking along the same lines as you...that maybe a fusible link could release the cable. Ray

[MGVWfan]

Yeah, I fabbed up a bracket for the T1 Mexican tstat out of 1'' galvanized steel strap, bent it near one end to put the butt end of the T1 tstat near where the Wahler tstat was. Works quite well actually.

Interesting, that memory wire might just allow for a degree of proportional control, too, like the original tstat...PWM the current in it using the sensed air temp to keep the CHT within a range, with a "fail safe" Klixon-type safety tstat to put full voltage on it and cause it to expand completely in case of control circuit failure...add a fusible link as a second fail-safe, purely mechanical and utterly reliable. You could use the D-Jet CHT sensor as the input, that way you could be assured you're sensing the parameter you really care about, CHT, vice the jug cooling air exit T.

so any thoughts on the fusible link's melting point?

[albert]

,,MG,,AND ,RAY,, i have look in the corvair car,,1960-68,, and the thermostat look the samething witch the 412,, it is a 7 spear like typ2 and the 412 ( on the web. pict. )excepted the fixing bolt,, and we can buy in the corvair parts cataloge,,( one new factory start the construction for this ther. for ,,corvair parts distributor ) and one model too we can use is the model for the jeep 1960 +or- ,,it is the same model excepted he got a cover over the spears ,,( for to go in the wather ) we have just need to reemoove the ring cover over the spear and we have the thermostat for 180 dr,fr, choice for 2-3 différent dgr. on the market,, albert

[bradey bunch]

Of course! I always forget about corvairs as a source for ptoential parts, even though my dad had one. The corvair engineers made their thermostats failsafe. Clarks corvair would be a good place to look...

http://clarkscorvair.com/

look at the bottom of this one

http://www.corvair.com/user-cgi/catalog ... IN&page=20

[MGVWfan]

Yeah, good thought that. I was looking into those, too...

http://store.lscorvairparts.com/product ... cts_id=580

http://www.corvair.com/user-cgi/search.cgi?part=C50AM

They look just like the Wahler bellow-type tstats VW used. I've been reading that the Corvair community had seen the same sort of corrosion problem with their NOS tstats I had (can't find the link to the website, argh!), for the same reason...they sit on the shelf for a long time, any little specks of brazing flux left on the bellows from assembly has time to eat them up. It probably takes 10-20 years for the effect to manifest itself, which is why the NOS stuff for both 'Vairs and VW's doesn't seem to last very long (especially in wet climates like SE Texas). At $56 a pop, I'd rather not have to take my chances with failure in 6 months or so...but if anyone else has experience with these 'Vair tstats, please let us know! If they last longer than the NOS Wahler VW tstats, they'd be a decent substitute, then.

One new wrinkle, however...I've read that someone's making NEW 'Vair tstats, which may solve the NOS corrosion problem. Haven't seen them for sale, just heard of the possibility.

As for Albert's thought of using the bellows capsule from a WC tstat (like a '60 or so Jeep), that has promise, if the tstat produces the required delta length at the correct temperature. The T4 and T1 cooling flaps need about 20mm (3/4") of travel to go from fully closed to fully open, and most WC tstats have half that travel to open their poppet valve. But, it's also an interesting thought. MGB's and just about every British car from the 60's on back used to have a bellows-type thermostat with a bypass sleeve that moved with the poppet valve, but it's been impossible to find that type tstat for 20 years at least.

However, here's one being made for the "brand X" (Triumph) TR4, for the numbers-matching restoration crowd, it's got the bellows and moving heater bypass blanking sleeve:

http://mossmotors.com/Shop/MoreInfo.asp ... nguageID=1

It's #10 in the following link, note the price!

http://mossmotors.com/Shop/ViewProducts ... =29120#top

Not sure for $67 I'd want to buy one and disassemble it for the bellows, though.

[albert]

HELLO,,MG,,i have the best solution for the thermostat but not for same ,,mony,,, like 100.$ ,,the systhem is very simple,, sentystat,, or sensitive thermostat,, you can geeve différent name,, the systhem is that ( a got the pict.) for the home heathing systhem,, for to open or close air duck damper,,(like vw )the construction is ,,,we have électric résistance sensor in the air duck,, 3'' long,, 1/4 DIAM. and for to epen the dempor with the temp. we have a 12 volt motor and a small geer box,, and connecting road 5'' long ,( adjustable ) , the motor take appx 5 minutes for to moove 5'' for to close or open complitley the damper,, and the randge for the sensy thermostat is from ,,30 dg,fr. to 300 dr.fr. or we can by for différent dr,fr, i d,t have the full description in my hand but i can look in my ,,cpu,,for to find ,, the factory name and description,,,,albert

[Piledriver]

HELLO,,MG,,i have the best solution for the thermostat but not for same ,,mony,,, like 100.$ ,,the systhem is very simple,, sentystat,, or sensitive thermostat,, you can geeve différent name,, the systhem is that ( a got the pict.) for the home heathing systhem,, for to open or close air duck damper,,(like vw )the construction is ,,,we have électric résistance sensor in the air duck,, 3'' long,, 1/4 DIAM. and for to epen the dempor with the temp. we have a 12 volt motor and a small geer box,, and connecting road 5'' long ,( adjustable ) , the motor take appx 5 minutes for to moove 5'' for to close or open complitley the damper,, and the randge for the sensy thermostat is from ,,30 dg,fr. to 300 dr.fr. or we can by for différent dr,fr, i d,t have the full description in my hand but i can look in my ,,cpu,,for to find ,, the factory name and description,,,,albert

Like a bimetallic coil spring and lever arm? (wrapped around a shaft)
(I'm thinking you should try something like that Ray, using the memory wire)

[albert]

no,PILL,, it is an électronic temp. controle,, the sensor 3'' is hot wire résistive wire ,,like you have for the gas heather in the air duck,and the small électronic board controle the positive courant on the motor ,, for to play the air flap ,, and we have adjusment on the controle for the temp,,albert

[MGVWfan]

Albert's thinking of having a motorized damper connected to the flap lever, with a control circuit sensing cooling exit air T or CHT. It'd be a good solution, if you can find a damper motor that's small enough to fit in the engine bay (especially problematic with the Variant engine bay), and will take the heat and fumes in the engine bay, and operates from 12V. You could even tap the existing D-Jet or L-Jet CHT line for a temp sample. Albert, you know of a damper motor that fits the bill?

[albert]

MG,, the box,,, include the motor, électronic board,,plus the gear box and the cam,,is appx. 2''1/2 deep and 4''x4''and the sensor probe is witch 2 wire,,the description is like that,,, if we want ( example ) 180 dr,fr. we adjust the knob at 180 and the électronic board controle the damper for to keep 180 dr,fr, with 1 at 9 dr,fr. différential,adjustable,,if we have 185 dr,fr, the damper open for to geeve more air or close if we have 175 dr,fr,we have many application for this controle,, you can see this flap controle in many ac or commercial heathing systhem,,wend i find the model in my ,,pc,, i send you the pict, ,,albert

[raygreenwood]

HELLO,,MG,,i have the best solution for the thermostat but not for same ,,mony,,, like 100.$ ,,the systhem is very simple,, sentystat,, or sensitive thermostat,, you can geeve différent name,, the systhem is that ( a got the pict.) for the home heathing systhem,, for to open or close air duck damper,,(like vw )the construction is ,,,we have électric résistance sensor in the air duck,, 3'' long,, 1/4 DIAM. and for to epen the dempor with the temp. we have a 12 volt motor and a small geer box,, and connecting road 5'' long ,( adjustable ) , the motor take appx 5 minutes for to moove 5'' for to close or open complitley the damper,, and the randge for the sensy thermostat is from ,,30 dg,fr. to 300 dr.fr. or we can by for différent dr,fr, i d,t have the full description in my hand but i can look in my ,,cpu,,for to find ,, the factory name and description,,,,albert

Like a bimetallic coil spring and lever arm? (wrapped around a shaft)
(I'm thinking you should try something like that Ray, using the memory wire)

Its already one of my backburner projects. I'm thinking about a fat version of the coil that is found in a pict-3 choke . I let you know how it goes. Ray

[MGVWfan]

Another interesting idea. Auto choke bimetallic tstats usually are made to open and close against very minimal forces (like the choke blade without a spring return)...the T4 flap return spring (if you keep it as a fail-safe) has so much pull, it will most likely overwhelm an auto choke tstat (like on Webers, Solexes. and MoPars). I've messed with the choke tstat from a MoPar slant 6, it's even got a long operating rod like we need, but not enough pull...I wonder if the physics of a bimetallic tstat make it impractical to generate more than a pound or two of force in a reasonably sized coil. Of course, you could pull the fail-safe spring, then the tstat should generate enough force to open and close the flaps.

[raygreenwood]

Actually bi-metallic strip forces can generate significant pull. I'm thinking of a "design" like a choke but with metal thicknesses about .050" and width of about 1/2" wide.

The two strips will have to be held together first and then heated...and then coiled while hot. Then the edges will have to be joined by solder.
The one thing that cannot be denied is metal expansion and contraction. It less than something like a trapped liquid that is frozen or heated....but still significant. If that force is then multiplied by lever length.....I think it can be done. Ray

[albert]

REY,, the bi-metalic spring is excellent ,,but tooday we can buy that only for the home,, cheminy damper,,,i d,t know more application,,,like i have see for commercial,ac,,, motorrised damper for fire protection,,made by honeywell,,but the motorised damper ( 20 model) is more expensive,but he geeve an excelant présition,,for the dg,fr, albert