Thermostats

[Patrick67BJ8]

I have a few questions about the different types of thermostats I have for my Healey.

I have three thermostats that appear to be nearly identical to originals and one that I just removed from my engine in prep for engine and radiator flushing. The three thermostats on the left of the photo are nearly identical and the right one is the one I just took out.

Do the three larger thermostats blankoff rings rise when the engine temp coolant gets hot? Do the blankoff rings rise enough to close off the head port? Does the blankoff ring lower, goes down, to close off the head port?

My wife won’t let me test the thermostats in her pots on the stove!

 

[bdcvg]

Yes, The rings aid more rapid heating of he engine block then move to supply heat to the cabin.

 

[WHT]

Yes, the ring is mounted to the top of the bellows and it rises when the bellows expands.

Check your thermostat after she leaves on a errand.


Good info at: > Bellows Thermostats <

"The motor in a bellows thermostat is a sealed beryllium copper or bronze bellows which has a liquid charge of alcohol or volatile oil. The set point temperature is determined by the boiling point of the charge. Since the back side of the bellows is permanently fixed to the frame, the pin and sleeve (bypass versions) ride on the face of the bellows. When the fluid vaporizes, the bellows expands, pushing the pin forward, opening the radiator passage and closing the bypass. There is a physical stop which also serves as a guide for the pin. There is no need for a return spring in a bellows thermostat: when the working fluid cools and condenses, a partial vacuum forms and draws the bellows tightly closed. When hot, the bellows itself acts a spring which helps open the thermostat, and this spring effect plays a critical role in regulating the response of the thermostat. It will also cause the thermostat to "fail open" in the even there's a leak.

For British engines with sleeve or slotted bypass systems, there is should be a sleeve mounted on the bellows. Thermostats without sleeves should not be used for these applications.

Never run a bellows thermostat above 4lbs pressure. The most critical point is that the charge will be in a vapor state when the thermostat is open. Once the charge is vaporized, the bellows is very compressible and it will act like an aneroid barometer. Which is to say, that it is very sensitive to pressure. So it should come as no surprise that they were not really intended for modern pressurized cooling systems. Care must be taken that system pressures are kept low, otherwise the thermostat can be literally squeezed out of calibration. For this reason, the radiator pressure cap should be rated at no more than 4lbs when a bellows thermostat is employed. These thermostats were rendered obsolete by pressurized cooling systems, and were complete anachronisms by the 1960's."

 

[Bob_Spidell]

The one on the right is a Robertshaw brand--repackaged by others--thermostat that wasn't manufactured with a sleeve, but some aftermarket sellers added them (note the solder joint on the bottom of the sleeve). The bellows-type, at least the originals, are 'fail close,' which means your car could overheat if they fail. Moss sells a 'fail open' thermostat, but I don't know if it's bellows-type or other. I bought an original bellows-type from a seller in the Netherlands, but haven't installed it due to fail closed.

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Six-cyl cars run a 7psi thermostat.

 

[WHT]

Bob, the original bellows thermostat failure modes are not certain.

As Popeye often said: "Yous pays yous money and yous takes yous choice (actually Punch in 1846)".

The original thermostat bellows were designed to act as a weak spring (failure mode open), but were primarily driven by pressure changes. I have no knowledge of the latest Chinese varients.

Metal fatigue and leaks are most likely to occur when the bellows is in the open position when hot and under pressure. If so, it will not develop lower pressure internally as it cools and the bellows will stay open. A cool, sealed bellows closes (and stays closed) because its internal pressure is lower than ambient pressure.

However, real world response is not always as planned. As you say, the the bellows could fail in the cool (lower pressure) position when closed, and the "weak spring" might not be sufficient to open the thermostat completely.

"There is no need for a return spring in a bellows thermostat: when the working fluid cools and condenses, a partial vacuum forms and draws the bellows tightly closed. When hot, the bellows itself acts a spring which helps open the thermostat, and this spring effect plays a critical role in regulating the response of the thermostat. It will also cause the thermostat to "fail open" in the even there's a leak."

The key words are: When hot, the bellows itself acts a spring which helps open the thermostat, and this spring effect plays a critical role in regulating the response of the thermostat.

 

[Patrick67BJ8]

These are the original boxes my spare parts thermostats came in. Thanks for the posting of the Robertshaw thermostat. I guess at sometime over several years I purchased that.

I think the bellows thermometers that I have are good to use so next I will search for a 4psi radiator cap. I also downloaded MOSS thermostats photos from their catalog. How and why is the MOSS blank off ring used, with a non bellows thermostats?

 

[Patrick67BJ8]

I did more research and you have to understand whatbthosevTF1,2,34 codes mean when it comes to the operating temperature. I have a winter and summer thermostat in my parts inventory. BTW, I did not see what temp the MOSS thermostat is. I also noticed the huge price difference between the originals and afterwards thermostats. Maybe there’s a reason for the blank off ring?

 

[Healey Nut]

I have a few questions about the different types of thermostats I have for my Healey.

I have three thermostats that appear to be nearly identical to originals and one that I just removed from my engine in prep for engine and radiator flushing. The three thermostats on the left of the photo are nearly identical and the right one is the one I just took out.

Do the three larger thermostats blankoff rings rise when the engine temp coolant gets hot? Do the blankoff rings rise enough to close off the head port? Does the blankoff ring lower, goes down, to close off the head port?

My wife won’t let me test the thermostats in her pots on the stove!

View attachment 91487

Time to replace the wife if she won’t let you test them

 

[Patrick67BJ8]

Time to replace the wife if she won’t let you test them

Too expensive to do that! A I hope she never finds out that I put the wire wheels in the dishwasher pot scrubber setting.

 

[Healey Nut]

Too expensive to do that! A I hope she never finds out that I put the wire wheels in the dishwasher pot scrubber setting.

I won’t tell , it’s our secret

 

[Bob_Spidell]

Do you have a grill?

 

[Patrick67BJ8]

Do you have a grill?

Outside bbq grill.

 

[Bob_Spidell]

Should be able to boil a pot of water on it. If you do, please report results.

To me, "the original bellows thermostat failure modes are not certain" reads as 'not reliable; hence not suitable for a car that is actually driven.'

 

[red57]

Never run a bellows thermostat above 4lbs pressure. The most critical point is that the charge will be in a vapor state when the thermostat is open. Once the charge is vaporized, the bellows is very compressible and it will act like an aneroid barometer. Which is to say, that it is very sensitive to pressure. So it should come as no surprise that they were not really intended for modern pressurized cooling systems. Care must be taken that system pressures are kept low, otherwise the thermostat can be literally squeezed out of calibration. For this reason, the radiator pressure cap should be rated at no more than 4lbs when a bellows thermostat is employed. These thermostats were rendered obsolete by pressurized cooling systems, and were complete anachronisms by the 1960's."

This is new information to me. I have never heard about the 4 psi limit.

In reading the Bentley Book it clearly states in section C.9 that "commencing with engine no. 3099 (approx. Sept. '58) a new thermostat was introduced to suit the 7 lb. radiator fill cap (BN4 and clearly shows pictures of a sleeved bellows tytpe thermostat).

And then later, in section CCC.2, "a non- bellows wax element type thermostat, interchangeable with the bellow type used previously, was introduced with engine 29F/2592" (approx. Dec. '62).

So that reads to me that bellows were used in conjunction with 7 psi radiator caps from Sept. '58 to Dec. '62 - a little over 4 years. Were they a special bellows that was designed for 7 psi?

I ask because I finally found and installed a sleeved bellows type for the first time ever and thought I was doing a good thing for my motor???

 

[WHT]

red57,

All I can say is that two years ago I tried to find a bellows thermostat that was proven to be reliable at 7 PSI (and slightly above 7 PSI); and spent several weeks looking for information and real world test results (not just vendor claims). I could not find a bellows thermostat that was known to be consistently reliable at these pressures. Moss sells one that they say is good from 4 PSI to 7 PSI. But, after 20 years of sometimes poor performing purchases, I don't always trust third world parts anymore (I do believe they are completely reliable at 4 PSI and below).

Barney Gaylord, who is well known from The MGA With An Attitude, published a warning from a Robert Shaw thermostat engineer saying: "With the introduction of higher pressurized cooling systems, manufacturers discovered that the system pressure would cause the bellows thermostats to operate erratically".

Barney then tested several bellows thermostats and found they all closed around 7 PSI. So, from what has been documented, 7 PSI seems to be a fairly hard limit when they are new. Who knows how that changes with several years of use when the weak bellow spring effect that helps open the thermostat aged? Robert Shaw found they could close and open erratically at this system pressure. I did not want to take a chance a bellows thermostat would stop working when it was needed most.

Please see the Moss and Barney Gaylord comments below:

Moss Motors - For the TR2, 3, 4, 4A, Austin-Healey 100, 100-6 & 3000, and MGA:

Thermostat, Bellows-Type, 160° F
This is a Moss reproduction of the OE-type bellows thermostat, with a sleeve to block off by-pass when the thermostat opens. This is suitable for systems using 4-7 lbs/sq in. radiator caps as was original. For pressures over 7 lbs/sq in, use 454-155, a wax capsule-thermostat that also has a sleeve to block off the bypass. The reason you can’t use a 434-165 bellows-type thermostat with a cap rated over 7 lbs/sq in is because the pressure in the system collapses the bellows, opening the bypass and causing increased operating temperatures, and possibly overheating.
Part # 434-156

The MGA With An Attitude - ADDENDUM:

Pat Jenkins is a thermostat engineer for Robertshaw.
At 12:08 AM 10/20/04 +0000, Pat Jenkins <jenko@comcast.net> wrote:
"With the introduction of higher pressurized cooling systems, manufacturers discovered that the system pressure would cause the bellows thermostats to operate erratically".

Well that makes sense. The bellows is a bit more than 1 inch diameter, so about 1 sq-in area on one end. Working pressure in the cooling system would apply force on the ends of the bellows tending to close the thermostat (about 1 pound of force for each 1 psi of pressure). To test this I put the bellows thermostat in a pan of boiling water to bring it to the full open position. I then applied force to the valve plate with a spring scale. Seven pounds of force was enough to completely close the valve, so indeed the bellows type thermostat may not open at all when used in a pressurized cooling system. I guess I won't be installing this one in my MGA.

 

[Patrick67BJ8]

red57,

All I can say is that two years ago I tried to find a bellows thermostat that was proven to be reliable at 7 PSI (and slightly above 7 PSI); and spent several weeks looking for information and real world test results (not just vendor claims). I could not find a bellows thermostat that was known to be consistently reliable at these pressures. Moss sells one that they say is good from 4 PSI to 7 PSI. But, after 20 years of sometimes poor performing purchases, I don't especially trust Moss and their third world parts anymore (they are completely reliable at 4 PSI and below).

Barney Gaylord, who is well known from The MGA With An Attitude, published a warning from a Robert Shaw thermostat engineer saying: "With the introduction of higher pressurized cooling systems, manufacturers discovered that the system pressure would cause the bellows thermostats to operate erratically".

Barney then tested several bellows thermostats and found they all closed around 7 PSI. So, from what has been documented, 7 PSI seems to be a fairly hard limit when they are new. Who knows how that changes with several years of use when the weak bellow spring effect that helps open the thermostat aged? Robert Shaw found they could close and open erratically at this system pressure. I did not want to take a chance a bellow thermostat would stop working when it was needed most.

Please see the Moss and Barney Gaylord comments below:

Moss Motors - For the TR2, 3, 4, 4A, Austin-Healey 100, 100-6 & 3000, and MGA:

Thermostat, Bellows-Type, 160° F
This is a Moss reproduction of the OE-type bellows thermostat, with a sleeve to block off by-pass when the thermostat opens. This is suitable for systems using 4-7 lbs/sq in. radiator caps as was original. For pressures over 7 lbs/sq in, use 454-155, a wax capsule-thermostat that also has a sleeve to block off the bypass. The reason you can’t use a 434-165 bellows-type thermostat with a cap rated over 7 lbs/sq in is because the pressure in the system collapses the bellows, opening the bypass and causing increased operating temperatures, and possibly overheating.
Part # 434-156

The MGA With An Attitude - ADDENDUM:

Pat Jenkins is a thermostat engineer for Robertshaw.
At 12:08 AM 10/20/04 +0000, Pat Jenkins <jenko@comcast.net> wrote:
"With the introduction of higher pressurized cooling systems, manufacturers discovered that the system pressure would cause the bellows thermostats to operate erratically".

Well that makes sense. The bellows is a bit more than 1 inch diameter, so about 1 sq-in area on one end. Working pressure in the cooling system would apply force on the ends of the bellows tending to close the thermostat (about 1 pound of force for each 1 psi of pressure). To test this I put the bellows thermostat in a pan of boiling water to bring it to the full open position. I then applied force to the valve plate with a spring scale. Seven pounds of force was enough to completely close the valve, so indeed the bellows type thermostat may not open at all when used in a pressurized cooling system. I guess I won't be installing this one in my MGA.

Thanks for the research WHT.
I found the same and similar info on my googling last night.
I will do some more research today, but I will hold off on doing my own testing because it has already been done by other people. The Triumph & Jag forums also have similar info and results.

What about using a puke tank/coolant overflow, would that be a better choice than a radiator psi type of cap?

Also, would using a $7 dollar non-bellowed thermostat with a blank off ring be of any use or advantage/disadvantage?

 

[red57]

I agree, thank you for the research WHT and I am wondering what thermostat (source/type) have you chosen for your engine?

I also wonder if the blanking ring and common thermostat work as well as the sleeved type?

Any conclusions welcome.

 

[WHT]

Patrick

Good luck with your cooling system. Although, I am not sure anything will really help much when it is 104F to 108F day-after-day as it has been this summer.

red57

There really isn't a perfect solution. For what it is worth, I use a sleeved wax thermostat; watch the temperature gauge religiously and carry a spare thermostat and gasket in case of failure. So far so good.

You can hedge your bets by using partial blanking.

 

[Patrick67BJ8]

I talked with David Nock today and told him what I removed from my car and what I had in the way of the bellowed thermostats.

he was familiar with both and said not to use the bellowed thermostats because they fail closed and you will overheat quickly.

David told me what he had and I ordered that and I should have it on Monday. I will post photos as soon as I receive it.

Thanks to all who participated on this post

 

[John Turney]

I use a non-bellows thermostat and

I agree, thank you for the research WHT and I am wondering what thermostat (source/type) have you chosen for your engine?

I also wonder if the blanking ring and common thermostat work as well as the sleeved type?

Any conclusions welcome.

I use a non-bellows common thermostat with the blanking ring on my 3000 engine. Seems to work fine. Supposedly, it takes longer to warm the engine, but I don't drive in freezing weather anyway. The blanking ring has some small holes to let air out of the head. The major worry is that the rim of the blanking ring + the thermostat + gasket can be a bit thick for the groove, so one might have to deepen the groove.