Thermostats for the XK120: a study

Thermostat for XK120
Here is what I “think” I know, after some tests and measurements of two XK120 thermostats. (I say “think” pending your confirmations or errata. )
The XK120 thermostat housing: I used/measured a re-pop XK120 thermostat housing, new, from Welch. It may be slightly different than an original. Rob Reilly found very slightly different measurements. The inside main passage ID, inside of the machined lip indent is 50mm., at the indent outer edge has ID is 54mm, the machined indent at the lip 1.1 mm deep, the thermostat flange lip is 1.1, so both thermostats slip in and then are flush with the mount surface. Compare the 50mm to the 54mm and it gives the machined indent as 4mm wide. The thermostat flange lip is 53.9mm so the thermostats fit closely, with tiny clearance. The bypass on this housing is round, a 10mm opening. (FYI far end the exit to the bypass hose is 13mm ID). The bypass round hole is at its top 5/16 (.3215, 8mm) below the housing flat surface, thus 18mm at the hole lower edge. This is what the sleeve needs to cover to close the bypass port to the engine. This location and hole size is important as the thermostat sleeve needs to cover/close it when warm, but have it open and not obstructed when cold. As we will see neither thermostat avoided cold obstruction perfectly but one was better. FYI, the main large top hose passage on the thermostat housing, is ID 29mm and OD 37.7mm.
Now for the sleeve-bellows Smiths type thermostat: I tested a Smiths 85025/80 and a Remax manufactured Made in England code P154 68C…( I believe made for Quintin Hazell by Remax) The QH number would be QT100…this one is stamped NT100 68C P154. In appearance and all measurements they are nearly identical. The AC has a minor difference that makes no difference. The Smiths and Remax seem identical and are quite possibly the same actual manufacturer The thermostat flange lip fits the housing indent perfectly with less than 1mm clearance. When in place the sleeve is visible thru the bypass: notable is that it blocks about 20% of the bypass opening. The thermostat sleeve is 16mm in its height (Same for the Smiths 16.3mm) (BK cites 15mm…no matter, there is and must be clearance between sleeve and the housing so the sleeve can move freely, this means a very small amount of coolant can pass to the bypass hole but it is a restricted path when the thermostat poppet is at full open so most coolant will follow the least resistance path to the radiator.) and 48.3mm sleeve width (diameter). When closed the sleeve upper edge iis 15-16mm below the upper thermostat flat. The stop (cross bar under the flange on the Smiths and on the nearly identical Remax are slightly different than the AC: The stop act upon and stop inside of the sleeve, on the bellows top. The AC has a lower stop, but also a lower bellows top, thus the same available travel. When closed there is no coolant passage thru the thermostat to radiator. It is open to bypass only—with some volume blockage but the bypass hole is small anyway. The Jaguar Factory Service Manual provides specs: starts to open 60-63C, full open at 80C and 3/8inch (9.5mm lift).

I also have in front of me, the AC TF-1. It is marked 72C on top of the flange, with AC manufacture code 2235, “AC Made in England” on the base. The later blue box/white horiz stripe (some have yellow) has AC Delco Davison of general Motors Ltd. Dunstable England. The dimensions closely match the Smiths: flange 54mm, 48.3 sleeve diam, sleeve height 16mm, the stop is apprx 9 mm below the inside of the flange, the Smiths a mm or 2 less. However, n the AC there is a 2mm greater distance inside the sleeve, from sleeve edge to the bellows top: it is 4mm and it is approx 6mm from sleeve edge to the stop) (it is more dished than the Smiths-Remax) which is what acts upon the stop (if it reaches the stop on full open it is a total of approx 9.5-10mm). The AC is much more dished from sleeve edge to the inner bellows top, whereas the Smiths and Remax are not but the stop is itself different (lower) so it comes out the same with 9.5mm to 10mm of possible opening travel. The 9.5mm lift is the important part as that is how far the sleeve moves up to close the bypass port. You can use any of the bellows sleeve ‘stats with the various temperatures. XK120s will mostly run at coolant temps that will have the thermostat full open all the time, the exception being the “winter” 86C thermostat. The others are 68C to 73C, and one at 80C which is still a quite acceptable operating temp.
NOTE these check points: All the thermostats install into the housing with the sleeve inside the housing. The thermostat must be installed, positioned so that the one of the two side flats does NOT block the bypass hole: if they are in the way the flat can block the bypass hole partially or completely. At the same time the piddle or air hole should be at 12 o’clock. Be sure that the sleeve has clearance to the housing, and also to the inner bellows (I had one with a sleeve that was cockeyed, so was against the inner bellows which could inhibit its travel. ) These are important install notes for the any thermostat. The side flat type of blockage is a lesser issue with the C3731/1 or 09-0160 as the side flats are not on the outer edges. I heated the thermostat installed in the housing with the whole assembly in the pot. When the thermostat opens, the top poppet within the lid extends to open about 9.5 to 10mm to allow coolant to radiator; at the same time the sleeve rises and DOES block off and close the bypass completely. There remains a space from sleeve to the upper thermostat flange of 5.8mm when the thermostat is full open, likely at the stop. There is a piddle valve, flopping around in the tiny hole at the top edge of the thermostat: …it “piddles” all the time, thermostat hot or cold. This aids in removal of air from the system when filling cold. The poppet travels to its open position in the same direction as coolant flow, closes against the flow. The Smiths type sleeve moves up, being quite low when cold, it has little bypass blockage when the thermostat is closed. It closes the bypass completely as it should when the thermostat is open. It is likely that if the thermostat failed, maybe the alcohol had leaked out, it would not open, thus fail closed.So the bellows/sleeve thermostat does what it is supposed to do which is no surprise, as Jaguar specified this thermostat. The Smiths 85025/80 and the Remax NT100/68, and AC TF1 have identical dimension measurements. . My tests on a NOS Smiths 85025/80 showed the sleeve at the low-cold point is 16.6mm below the inside of the top flange. When fully open the sleeve is 6.5 mm below the inside of the top flange, thus the sleeve moved up 10.1mm: The thermostat reacts very quickly to cool and close to radiator: as soon as out of the hot water the sleeve starts to drop and the poppet starts to close.

Now for the XKs 09-0160 thermostat: a different design,(actually 2, or more versions exist) it has the sleeve mounted, so that when cold it is at the top, right under the flange, not at the bottom. It has a cone top in the 3 bar version; and a rounded top in the 1 bar version, but neither are flat as is the Smiths type. The brass rounded center top, single top bar version does have a very small hole in the top plate (flange) so that air could pass during a fill when cold and closed. I did not find any such hole in the silver, cone top, 3 bar, closed bottom version which could be a problem with this version, in trapping air in a drain and refill. Would any air in the system, once thermostat fully opens, then be moved with the coolant flow into the radiator space? Both of this type are smaller overall in mass, but the top flange also fits exactly in the 54mm slot. The top mounted sleeve is 12mm in height, (less than the 16mm of the Smiths type) , and 49mm wide (diameter), 1mm more than the Smiths, so fits in the 50mm diameter housing with 1/2 of 1mm clearance around it which when closed to bypass would allow a very very small amount of coolant to the bypass. This thermostat, from the underside of the top flange lip, to the lower part of the top positioned sleeve is 16mm, so cold, with the thermostat closed, and bypass open, blockage from the sleeve occurs. But,noticeable, even more than than the Smiths type where the sleeve is at the low end and out of the way, this top mounted sleeve blocks about 35% of the bypass, while at the same time the path to radiator is totally closed. Cold, closed to radiator, open to bypass, you can see a lot of the sleeve thru the bypass port. When heated the thermostat opens as it should, the poppet opens about 9mm (the Smiths type was 10mm on my test, tho 9.5 is the spec. ( One can expect variance in 60 year old thermostats…if they work at all, so do test before install) and at the same time this sleeve moves DOWN to close the bypass which it does completely. The bypass is closed, and port to radiator open. So it works: minus the issue of the bypass to engine opening being more than half obstructed at a time when the thermostat is closed and directing all coolant to the bypass: Coolant can flow around the thermostat base, so maybe this matters, maybe not, as long as enough coolant is flowing thru the port to the block to prevent super-hot spots. So, the later model, C3731/1 -09-0160 works: the sleeve moves DOWN to block the bypass. The sleeve blocks about 35% of the bypass at a time when it should not. It has no piddle valve but DOES have small air hole in the top. If the thermostat failed, it would also likely fail closed to radiator, but it depends on how/way it fails.

And now for the new entry: the currently manufactured Moss 434 156 bellows sleeve thermostat: The Moss Europe bellows / sleeve thermostat’s flange diameter, and sleeve diameter meet the Jaguar spec already discussed. The Moss sleeve is 16.256mm wide, wide to mean its height in the terms we have been discussing. We know the relevant Smiths sleeve is 16mm in height: looking good, a very small bit wider (more height) certainly no harm done, likely an aid. Now as to sleeve travel, the Moss sleeve travels 8.382mm of sleeve travel. We know the Smiths has 9.5mm to 10mm: , I am concerned about there being 1.118mm less travel and still completely covering the bypass port-hole. It does ain 1.256mm back in its height. Does that mean it will cover the bypass port despite less travel? We shall see. Close is enough in horseshoes and hand-grenades. Lee said his test of a Smiths with 8.5 travel did not close the bypass, (my opinion is that his test Smiths thermostat did not fully function thus the 8.25mm observed instead of the 9.5mm that is known to be the Smiths spec.) The Moss with less travel but more sleeve height may just do it,but I have to withhold stating that the Moss bellows/sleeve is applicable to the Jaguar cars until actually tested in the relevant housings. Does it fit in the housing? , Yes. Will it open flow to radiator? Yes. But will it close the flow to bypass sufficiently? I hope so. It may be that the sleeve stops could be modified to allow more travel. A $123.99 part that is new, is likely better than a hard to find $70 NOS that is 60 years old, and I won’t be the one to whine. It may be one of the less costly things I would do in maintenance of a XK120.

About the job of the thermostat: it’s job is to allow the engine to warm the coolant to optimal engine operating temp: good for lubrication, fuel ratios, combustion, etc. Then when coolant becomes too hot, the magic little thermostat works to cool the coolant by allowing the radiator to do its job. The thermostat should cycle: closed to radiator at start up, then as coolant warms opens to radiator, then cycles closed to radiator while open to engine , and on and on. The coolant “should” stay close to the temperature of the spec of the thermostat. If you have a 72C then op temp should be close to that: if you have an 82C then close to that. A higher temp thermostat in and of itself, does not make the coolant overheat, but it does take away some margin that may be needed due to other cooling system issues. That said, Dick Maury says, “if a car is running hot, the fix is NOT a change to a lower temperature thermostat. The thermostat only controls the minimum operating temperature of the engine. If the car is overheating beyond the rating of the thermostat, the excess heat is beyond any thermostat control: the thermostat is open, job done. Only the radiator can now do the cooling. Changing to a lower temperature will only cause the engine to run cooler when warming up. Once the thermostat is open, it is open. Because these thermostats often fail closed, is why a sudden overheat is likely a failed thermostat. For 140 150 folks your thermostat placement is in a different place:…if the bypass location dimensions and placement are similar to the 120 housing, then all should be as for the 120,
The XK radiator cap must be 4lb, maximum, do not use the 7lb or 10lb thinking you can now operate at higher coolant temps without boiling: this will cause the thermostat to fail, and they may fail closed, with no flow to the radiator which is very quickly not good, as this is how head gaskets and core plugs fail. Note also that the original red seal within the radiator filler neck is important with original type cap which does not have its own seal within (a later cap may have the rubber seal within the cap.) Be sure there is a “witness”mark on the cap rubber seal.
Finally we are likely to end up stressed, when engine heat production exceeds the capacity of the radiator to cool the coolant. The thermostat is wide open doing all it can, the radiator is doing all it can, and the coolant temperature continues to rise. That is when we realize that we are in our beloved vintage automobile, with a vintage cooling system, likely a lot of vintage crud within it, while the vintage temperature needle keeps moving toward the vintage peg.+
Credit due to many forum posters including Bob Knijnenburg Dick Maury, Rob Reilly, Roger Payne, Mike Balch, Michael Frank (+and MGA Guru…for the vintage wisdom) , and no doubt many others. Thanks. Most pleased for review and errata comments.

Many road test reports done in the day skirt the issue of cooling / over heating, but a few do report the issue as common, known to Jaguar, and wonder why it was not fixed in the XK120 models. Most said it was OK on the road…but if you are caught in traffic in summer…“just pull off the road, brother, you’ve had it.” Been there, done that !

A truckers tip: a small aftermarket windshield washer pump/with water reservoir can be installed hidden inside the fender well, a pump on off sw under dash, run two little rubber hoses with spray nozzles from pump to front sides of the radiator…when the temp creeps up to hi…hit the switch for a few seconds spray of water on the radiator front. (if an aux electric fan is installed even better when you switch that on as well) the temp will drop:…a few of these cycles may get you thru the traffic to clear sailing.

See separate post for “WHICH thermostat to use”
Nick
credit to: Bob Knijnenburg see http://www.bobine.nl/jaguar/02-engine/thermostats-for-jaguar-xk-120-140-and-150/

and FYI this discussion on the web:
http://www.mgcarz.com/thermostats.html

See Jaguar Journal Sept-Oct issue, and Nov -Dec…2016, or on line for the Bob Knijnenburg article on XK thermostats, with cross ref to the QH-QT100 series, and AC TF series bellows -sleeve stats that can still be found. The Chart below from Michael at XKs Unlimted, early Jaguar (Smiths) thermostats:
car Jaguar# Smiths # TempSpec Notes/later part#
XK-120 C3731 X.43655 63C X85025/60

XK-140 C3731/1 X.43570/5 72C X85025/72
XK-140 C7105 X.43605/3 86C X85025/86

XK-150 & XK-150 “S” C12867 168 F Standard
XK-150 & XK-150 “S” C12867/1 183 F Cold Climate

smiths%20thermostat at left, a Smiths type bellows/sleeve, 090160%20therm%20superstat and on the riht, the XKs bypass stat 090160 with sleeve at the upper end.


3

1h

This old XKs 090160 thermostat was available some years back but is not current: (above on wood with 3 cross bars on top and a cone) worked in my test in the XK120 application…the “top mounted” sleeve traveled down to block off the bypass. It does not have a small bleed hole. More on this version later. XKs now still has the 090160 on the web description, but also lists at the same time now, as part number , C3731/1. saying at the bottom of the view, that it supersedes the 090160.
I do not have means to test in a housing for 140/150 or early S1…but it “may” work as well. “May” because the 090160 sleeve is not as tall as the Smiths bellows type, thus covers less, and also it travels not from the bottom to up…but from the upper, downward to block the bypass. This may matter if it travels short or too far;!
Next case: the Barrett C3731/1, a single bar across the top, rounded center button on a brass top, a small bleed hole, a top mounted sleeve without bellows, spring is visible. SN%20Barrett%20therm%20sleeve%20type|500x500 090160%20therm%20superstat smiths%20thermostat ( SNG single top bar) a photo here also of the original type Smiths bellows/sleeve) Whether it in fact blocks the bypass completely on a 140/150, as it does on the 120 remains to be tested.
The SNG bypass thermostat…(and now the XKs as well) lists with the Jaguar part # C3731/1… but that means ONLY that they (SNG and XKs) selected that # designation for it, and determined or “feel” that it will do / fit what it is supposed to do where that # was specified by Jaguar. It is NOT a Jaguar part, nor are these thermostats the same as the Smiths type bellows/sleeve part that Jaguar used/installed at the factory. The SNG stat looks similar to the current XKs 090160…but some differences easily seen to the old Xks 3 bar version. Whether the sleeve moves “up”,.,or “down” is irrelevant IF: it is has enough sleeve material height to cover the bypass port; and if it moves enough, but not too far, to cover and close the bypass port. Seen here the SNG C3731/1, the XKs 090160, and a original type Smiths X85025. the old XKs has 3 bars, the current XKs C3731/1
090160 a single top bar & visible spring 090169%20view
The older 3 bar, cone, silver top, brass closed bottom with no spring visible- 090160 is a 160C…on the cold side. It has no mfg name mark, it has “J04” “160 G” (prob mis-stamp in China and meant to be a C), and “13” all on the bottom smallish copper button base. This 3 cross tie bars on the top, with no bleed hole has a bottom that looks nothing like the single top bar 090160 ,this one having a closed bottom, no visible spring.

shown, a little blurred.but obvious differences,
Nick

and the top view of the 3 top bar, cone, that has the brass closed bottom , no visible spring, and no air bleed hole.,
XKs currently lists the C3731/1 090160, and the photo they show now is the single top bar, spring visible…perhaps the same as the SNG…so maybe the exact same thermostat. But XKs shows it as not available, whether a temporary issue is not yet known.

Nick,

Thanks for the work you did: an indepth study on the behaviour of these bellows thermostats and the sleeve more in particular.

One remark regarding dimensions: there are different manufacturers over time and after Smiths ceased production, AC and Quinton Brivec took over but both manufactured already (bellow-type) thermostats when Smiths was still in production. This might explain the differences in dimensions you found.

The same is valid for a possible difference in “opening.behaviour” meaning some thermostat brands need 10C while others require 15C before they’re fully open (probably depending on the filling (gas) pressure of the bellows and the spring force). The latter should be read in conjunction with the discussions on the choice of opening temperature and the effect on the cooling of our XKs…

Regards,

Bob Knijnenburg

ALL of the C3731/1, COUNTER-moving thermostats, as sold by the usuals, are only partially effective on the 120, completely ineffective on the 140, yet serviceable for the 150 thru the S1 E. The market for these later cars is, of course, much larger that that of the 140 so it is understandable that the outlier 140 would be the red-headed step-child in all of this…tough luck for us 140 guys. And since the availability of the proper, NOS 'stats is sketchy, modifying the 140 system to use the modern, readily available parts seems to be the most practical course. That is why I reduced my bypass port from 1" down to about .34" to reduce potential bypass flow, as was suggested earlier by another poster.

For the 140, the XKs 090160, pictured above, appears to have a flat mounting flange (no turned up lip), rendering it even worse than the Barrett one since it would sit even further into the cavity than the Barrett unit.

Hi.,.my interest started as for the xk120,.,which I have…then expanded to the 140, 150, and early E, series 1 since they use the same bellows sleeve, that leads to the conclusion that although the location/housing is different in each, the dimensions for the placement must be approx the same, …but this is untested by me, and the main issue would be the size, shape and location of the bypass hole or slot. I have two Remax bellows sleeve that came in QH boxes…thermostats…marked NT, and 2 of the newer type that XKs have as the 090160…two variations, 3 bars at the poppet, or 1, and visible lower spring, or all enclosed brass, purchased some years apart. . .,. Prior to your work and article there was not much info.,.so thank you. Nick

Lee…curious as to your comment re the XK120: later thermostats counter move (you mean fm top downward to open) " only partially effective" . The two later thermostats I have, …both XKs 090160 type, but the 2 are different worked well, did totally close the pass, did open to radiator. The one with 3 top bars over the poppet does have a two step raise in the silver color top flange, while the one bar, exposed spring type is flat to its brass edges. So quite a few differences in that type–they both fit the 120 housing quite well, in the machined indent,
I do not have the Barrett one,but check the pics, I have tested these in the 120 housing,both work, close the bypass. I have no means to test the 140,

Interesting in the Factory Manual pD12 lower, for XK120 specs no brand at all, with a 60-63C commence openi, and 80C full open, 9.5mm lift. So the thermostat controlled max operating temp is 80C: we can say that since the from 60C the thermostat is increasingly part open to radiator AND decreasingly part open to bypass until full open at 80C. Thus the normal op temp is at the upper end of that range, let’s just say 70 to 80C.

An aside: For the Mark 7, spec thermostat Smiths commences to
open 70-75C and full open 90C, valve lift 9.5mm: but also lists the British Therm brand same opening, but full open at 75C, and in the supplement for the Mark7: From engine no NA1076 a modified thermostat C13944 is fitted replacing C3731/1. The bore in the pipe to take the thermostat has been increased by .25mm.in the.new housing C 14133. The new thermostat must not be fitted to a prior engine as the movement of the thermostat can be restricted by the smaller bore, C3731/1 Smiths X85025/74 74C, the new is Smiths 43570/5 73C
Nick

Rob Reilly provided measurements/photos of the 'stat housing for the 120. It showed that the block-off ring traveled about 1/8" past the opening of the bypass port…AND…was slightly too small in diameter as well…which may actually be the bigger issue. His helpful post is contained within another thread. And yes, “counter-movement” means from top down…or away from mounting flange.

As an aside, Reilly has a huge stock of terrific photos which have been very helpful over the years.

the 090160 I tested in the 120 housing completely covered the bypass hole, the diameter of the sleeve is 49mm, the inside diameter of the housing is 50mm, so 1/2 of 1mm clearance, yes…all the way round of course…, but that is quite a small path…when the path to radiator is fully open…(path of least resistance). The brass top, single top bar version does have a very small hole in the top plate so that air could pass during a fill when cold and closed, I did not find any such hole in the silver, 3 bar, closed bottom version which could be a problem with this version, in trapping air in a drain and refill. Would any air in the system, once thermostat fully opens, then be moved with the coolant flow into the radiator space? That noted, I’d say these thermostats are just fine for the Xk120,.
Nick

THIS thermostat looks to be the correct one for both the 120 AND the 140…note the small gap between the block-off ring and the mounting flange…well done, Kennedy!

Can you get a 1000 more?

what is it…is it a NOS old…Smiths or AC or QH, Remax? I just received a NOS Smiths I located ,smiths%20therm%20w%20box same as this, new in box, and I have 2 of the Remax NOS. T
he new Moss EU so far has measurements that match what we need.48.5 sleeve diameter, flange 54m.,just need sleeve heiht and sleeve travel., IF…its height is 15mm-16mm, and travel is 9.5mm-10mm…BINGO

This is the issue everyone seems to be overlooking. The XK120 Service Manual indicates the travel of the sleeve is 3/8 inch (9.5mm).

However, when you cross reference this to the XK120 Parts Catalogue you find that the 3/8 inch sleeve travel spec. is for the Smiths X.43655 thermostat, which has been obsolete for 60 years. The replacement thermostat is the Smiths X.85025, which has less sleeve travel. I measure the sleeve travel of my NOS Smiths X.85025 at only .325 inches (8.25 mm) as opposed to the original Smiths (X.43655) thermostat sleeve travel of .375 inches.

It is my understanding that the other manufacturers of bellows and sleeve thermostats (such as AC, Remax, QH, etc.) followed the later Smiths X.85025 specifications. Thus, none of the available bellows and sleeve thermostats are likely to resolve the bypass port issues of the XK120 or XK140.

In other words, the bypass port will not fully close when the main thermostat valve to the radiator is fully open. My measurements on an XK120 thermostat housing indicate that the sleeve closes-off only about 1/2 of the bypass port when the thermostat is fully open. In addition, there may be a sizable gap between the outside diameter of the thermostat sleeve and the inside diameter of the thermostat housing due to age and corrosion of the alloy thermostat housing.

This subject has been thoroughly covered on the E-Type forum over the past couple of months. What came to light is that Jaguar changed the location and width of the bypass port after the XK140. This
may have been to adjust to the changed specs of the later Smiths bypass thermostat.

points understood Mike…but check further…I have a NOS Smiths, several NOS QH, Remax, and AC…all in the numbers specified for our XKs. I tested both the NOS bellows sleeve and the newer ones with the top mounted sleeve…BOTH extended 9.5 to 10mm, both fully covered the bypass hole in the housing. Yes the sleeves are from 1/2 of 1mm to 1mm less diam than the ID of the housin, as they must be to have clearance to move freely, that is a tiny amount of possible coolant passae to enine, when the thermostat is open to radiator…easier path…and closed to engine. I find no problem. Maybe some NOS, 60 year old stats won’t open all the way to 9.5-10mm as when new.,.mine did. The Smiths which I tested was of course totally oriinal as to what Jaguar installed at the factory for many years of production,no revision, and I am convinced the thermostat operated in the XK120, 140, 150 ports adequately. I think you stat just didn’t age well, BTW…the 120, 140, 150 used the same dimension thermostats.,.just different fitted location…but the size did not change til much later…(xcept for Mk7)…,in the later E Type Series 1. The early Series 1.,same stat as the Xks, Nick

Lee,

I think I was fairly lucky getting this one. I have an early 120 with no heater so it isn’t the exact correct for my car (the one pictured is a Smiths 43570/28 73 degrees). It will have little effect as the 28 just kept the water warmer so the heater was more effective.

Matt

yes Matt…the spec temps don’t matter too much…tho a 60C may be a bit too cold…and a 86C a bit too warm. The /28 is a 73C…like Goldilocks bed…just right. Kinda nice to have a real Smiths…even tho it can’t be seen…you know…and…THIS is the currently manufactured, relatively new bellows-sleeve thermostat via Moss Europe, part 434 156, current retail $123.99 USD.
The Moss Europe bellows / sleeve thermostat’s flange diameter, and sleeve diameter meet the Jaguar spec, The Moss sleeve is 16.256mm wide, wide to mean its height in the terms we have been discussing. We know the relevant Smiths sleeve is 16.2 or .3 mm in height:, a very small bit wider (more height) certainly no harm done, likely an aid. Now as to sleeve travel, the Moss sleeve travels 8.382mm of sleeve travel. We know the Smiths has 9.5mm to 10mm: I am concerned about there being 1.118mm less travel and still completely covering the bypass port-hole. It does ain 1.256mm back in its height. Does that mean it will cover the bypass port despite less travel? We shall see. Close is enough in horseshoes and hand-grenades. Lee said his test with 8.5 travel did not close the bypass, (my opinion is that his test Smiths thermostat did not fully function thus the 8.5mm observed instead of the 9.5mm that is known to be the Smiths spec.) The Moss with less travel but more sleeve height may just do it,but I have to withhold stating that the Moss bellows/sleeve is applicable to the Jaguar cars until actually tested in the relevant housings. Does it fit in the housing? , Yes. Will it open flow to radiator? Yes. But will it close the flow to bypass sufficiently? I hope so. It may be that the sleeve stops could be modified to allow more travel. A $123.99 part that is new, is maybe better than a hard to find $70 NOS that is 60 years old, and I won’t be the one to whine. It may be one of the less costly things I would do in maintenance of a XK120.


Nick

think I said…I do not accept that one model number of the Smiths, has less sleeve travel than another. The only difference should be the operational temperatures. The hole for the thermostat bypass did not move., Smiths would not chane the travel. I suspect a malfunction in the test thermostat…which of course is why a replacement is sometimes needed…they fail in one way or another,and even a NOS 60 year old thermostat can not be assumed to be in perfect operation,
Mine open to 9.5 to 10mm
Nick

just to start in on the Xk140 details relative to thermostats…as they take the same thermostats, the bypass slot in a measured ‘140 manifold extends from .30” (7.62mm) to .60” ( 15.24) mm below the thermostat mounting surface, so the slot is .30 in (7.62mm) vertical dimension, top to bottom,
With the new Moss thermostat, similar to Smiths type.,.,but so far NOT specified for Jaguar (Triumph, Healy, ), the top of the ( cold) sleeve sits .10” ( 2.50mm from and below the slot opening.
When full open, the Moss sleeve rises upward by .30” ( 7.62mm )until it contacts the stops, leaving .10” (2.54 mm of slot uncovered by the sleeve.
If one could successfully file slightly more than .10”( 2.54) off of the stops, the sleeve should be able to rise that much further, for a total rise of 0.4 in (10.16mm) , enough to completely cover the slot. Would creating additional sleeve rise damage anything internal in the thermostat that could lead to failure? It would be nice to be able to use the Moss thermostat in the XKs.,.tests needed.
Nick

We have seen the 140 slot in 3 different manifolds, cast at 2 different foundries, measure from about .24"(or even less, in the case of mine) to .3" below the mounting surface. The photo the one poster posted shows the only one I’ve seen so far that would work for all 3 configurations (120, 140, 150/E/MK2) we are examining here…but…it is an nos, 60 year old part, which I don’t remember seeing the part number or manufacturer of. I do believe there were appropriate thermostats installed into these cars when new, and the one I just referenced seems to be just that…a period spare.

The question to me is whether we can locate a reasonably priced and readily-available supply of NEW parts that fit the bill. So far, it looks like only approximations are available (brand new) for the earliest cars…(the H-type carburated cars) which leave something to be desired.

Nevertheless, tremendous work done here by so many!

often there are several NOS sleeve bellows for Jaguar XK on ebay, …etypeparts, and bitsnpieces…, takes a bit to find em…type in "Smiths bellows sleeve , TF1 etc…be sure there is a sleeve…see my post.>>WHICH thermostats for the XK…there are quite a few that will work…must have the sleeve,m,.around 40-50 USD. Nick