Here is one for an early Mark VII.
Another interesting manifold. What is the diameter and depth of the bypass port?
Also, what is the depth of that ridge in the thermostat housing?
Nice recent posts with accurate measurements…now much closer to definitive .note that the xk120 had the thermostat in a separate housing attached to the radiator,: .it is.then the 140 onward that has it to the intake.
XK140: thermostat now at the intake manifold: but wait…that is not all…the 140 cooling system is improved over the 120: a different radiator, plus… The 140 has a 1 inch inside diameter bypass plumbing with the suction line
built into the casting of the water pump rather than an afterthought 1/2"
circuit as in the XK120. The 120 circuit necks down to 7/16" at the banjo
fitting and further down to two holes of .275" at the banjo bolt itself.
To make matters even worse, this xk120 banjo bolt at the water pump shares its
suction with the heater circuit with two more small holes of the same size for
it.
XK140,C7462 is the XK140 inlet manifold.
C7463 is the XK140 water outlet pipe for inlet manifold
as to thermostats themselves:
first, with the bellows type thermostat, about
75% of the flow area is blocked by the bellows and the bypass ring around it. Later types, but not applicable to bellows/sleeve applications, are more open to flow.
re the jiggle pin. Viart mentions it should be
on top to let air bubbles through when filling.
Then there is this: Jaguar Service Bulletin No. 235 of January 1958 informs dealers that a new thermostat version has been introduced for Mark7 that has an increased outer diameter. Although this increase of .010″ or 0.25 mm is rather small, Jaguar changed the “Water Outlet Pipe” (or thermostat housing) for (all?) XK engines as there was “ a possibility of the movement of the thermostat being restricted by the smaller bore water outlet pipe “. Note that SB 235 contained an error (wrong Smiths number quoted for old and new version) that has been corrected in SB 239 of February 1958 (although it contained a new typing error: X.850 24 /74 instead of X.850 25 /74). The SB does refer to the prior thermostat CX3731/1…thus that part number IS a Jaguar part number for the then used Smiths thermostat.
It is therefore possible that the later Smiths thermostats with part number (X.)85025/xx may touch the walls of the older water outlet pipes.
there were more Smiths thermostat-temperature versions available than the ones Jaguar had chosen. They are sometimes close to the nominal value Jaguar opted for. Example: 85025/70 instead of 85025/74. just a small temp spec difference.
Looks like we are closer to definitive:…as you suggest/request Michael, a do-over is needed in each model, with the relevant XK120 housing, and XK140/150/E Type manifolds in hand. We need to know the diameters in/out and bypass, and precise bypass slot location and size.
Nick
I’ll probably add a section on air bleeds…jiggle, ball valve, or simple hole after I publish the bypass section.
The rough goal with regard to bypass design is to keep a constant rate of coolant flow, regardless of thermostat position. It’s really impossible to get it right with this design, and was especially difficult using pencil and paper. Try drawing a sleeve thermostat and housing by hand, or calculate the flow cross sections for various lift heights, and you’ll see what I mean.
The perceived size of the port may not tell you much about the actual measurements of the flow cross section. The 140 port looks big, but a lot of it is cut into dead metal, the slot only partly breaks through into the bypass passage. This is true of all the slot-cut bypasses. What I think was going on is that they wanted bypass flow to stop earlier in the travel of the sleeve, which is easier to achieve with a rectangle than a circle. By the time they reached the 150 and E-Type, the slot was very skinny and would have been fully blocked for any appreciable sleeve travel. It really seems that they had a cooling problem that they didn’t know how to solve.
to your recent point.,.I like this…edited excerpt from the MG Guru.:
The problem we may finally run into happens when the engine load and heat production increase more than the capacity of the radiator to dispose of the heat. The thermostat is wide open doing all it can but the coolant temperature continues to rise. That is when we realize that we are dealing with a vintage cooling system, with its vintage design, likely some vintage internal crud and corrosion, and keep a close eye on the vintage temp needle while it creeps closer to the vintage peg.
There was just not enough open frontal area on the 120/140 to achieve sufficient air flow volume thru a suitably large radiator. All of my old Ford V8s have a constantly open, .5" bypass system , but, because of the huge radiator area and amount of water flow, this open bypass system worked just fine. IIRC, the Chevys used the same system.
What seems odd to me is IF Jag thought they had a problem overheating attributable to the bypass system, why in hell did they make the 140 bypass slot and hose several times larger than the 120’s?! They went from a hose of 1/2" on the 120 up to 1" on the 140.
I did some measurements and tests on a xk120 thermostat housing, with a Smiths type sleeve bellows thermostat, and an XKs 090160 thermostat installed, in a pot of hotwater: Both work, fit, but in different ways. Since it is just a XK120 experiment, …I have posted it on the XK forum, topic thermostats for the XK120 heading . But…,since the Series 1 is somewhat similar…have a look there. Similar test …thermostat in the respective manifold housings need to be done for XK140/150 , and Series 1. , as I only did the 120,. Nick
I liked the graph of bore wear vs temperature. When I was boring engines I noticed the greatest wear was where the cool water came in. Most engines had significant wear in only one cylinder but we ended up boring all cylinders. With removable sleeves this was easier to deal with. It did, of course, require the cost of repacing a sleeve but that was offset by not having to buy a set of OS pistons and a better feeling for keeping it std. size. I wondered if painting that impact area or creating a baffle might reduce wear at that point.
DKWs had a thermosiphon cooling system, with the radiator behind the engine: they commonly suffered “Colorado piston,” where the leading piston would wear badly, because it ran the coolest.
Dad figured this out, in the late 50s, and fabbed up a shield to mount in front of the engine, which largely fixed the problem.
( SNG single top bar) and the original type Smiths bellows/sleeve) Whether it in fact blocks the bypass completely, as it does on the 120 remains to be tested. The SNG bypass thermostat…lists with the Jaguar part # C3731/1 but that means ONLY that they (SNG) selected that # 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 is it like the Smiths type bellows/sleeve part that Jaguar used/installed at the factory. It looks similar to the current XKs C3731/1 090160…but some differences from the old one are easily seen. 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. th XKas
re the 140:…maybe the 120 flow in warm up was not quite enough to avoid hot spots?? Jaguar did improved the water pump, improved the radiator with different mounts, angle, grille , installed a new inlet manifold with coolant passage, and revised the distributor and timing: as Roger Payne points out,10bhp with only these revisions. Not too many 100F days in merry ol England: maybe they had not visited USA in summer.
Nick
Except they certainly knew by then that the 'muricans were THE market, lol.
I discussed both of those products earlier. AFAIK, the 090160 in your photo is no longer available from XK’s, and ordering the 090160 will get you the same thermostat that SNG sells as C3171/1. But let’s begin with 090160 as pictured. The donor thermostat was a Robertshaw, probably 333-160, made in the midwest, maybe Kentucky or Indiana. Robertshaw has gone through a series of corporate owners and I believe is currently manufactured in Mexico on an OE basis only, so no more retail products. There now are a few manufacturers that copy this same design, and quality is all over the place. 090160 added a bypass sleeve by soldering or brazing to the Robershaw poppet. The problem is that the design of the thermostat has always been misunderstood. The flow path is actually constricted to the area between the poppet and the bypass sleeve, nothing passes through the center. Soldering the control sleeve actually blocks part of the flow path. The donor thermostat was intended for use in engines where the flow enters from the sides of the housing, like a V8, where coolant flows from right and left banks to the center. In those applications, it’s a very high flowing thermostat. In Jag applications where flow enters from the back of the passage, it’s constrained and flows about the same as any other thermostat. This is how it’s intended to work in its native application:
I’ll have a whole page on this thermostat, only because it’s an interesting design. But it’s not really an ideal solution for a Jag.
SNG 3171/1 is a different rendition of the same idea. But the donor thermostat is from a Land Rover Ser II. It suffers a bit because the donor sleeve is tapered. So cutting it down also reduces the diameter by a millimeter or maybe less. Both thermostats will have a 3/8 sleeve and about 3/8 movement. And they’re wax thermostats, so they move backwards. You can use higher pressure caps with these thermostats, and that’s going to be a big advantage.
It really makes no sense to say much about the original Smiths or Teddington thermostats, as the stock has dwindled and they should be considered NLA. What may be more interesting is the Moss bellows stat, which I believe will work for all bellows applications.
yes…most xk120 were left H drive for export.
Need to obtain .the Moss Europe bellows…to determine its measurements and operation. Moss email to me declined to find the measurements,but said no problem to buy one, return if it does not fit,.,pricey around $100 or so. It would be quite something if it fit the Jaguar application for bellows sleeve…and also the Triumphs etc., Nick
I addressed that question earlier in this thread, including posting measurements.
I found your reference to the Moss 434 156…with 2 1/8 flange (53.9mm, and 48.5mm sleeve. So far…that matches closely what the Smiths, and the newer bypass stats are…and would fit the Jaguar XK120/140/150, early S1. Do you know what the sleeve height and travel is? If also similar, That could “seal” the deal for the new Moss Eu bellows sleeve that fits the Triumph. BTW Jaguar factory did use the thermostat part number C3731 and C3731/1, those part nos appear in the factory Technical Service Bulletins.
Nick
Also posted. The sleeve is .64" wide, and when fully extended, the gap between the top of the sleeve and the thermostat flange is .33". In other words, about the same dimensions as the Smith’s.
And to repeat…there were few models of thermostats available in the British market, so the cars tended to be designed around what was available. If there’s a missing link thermostat with different dimensions, it’s yet to appear.
The Moss thermostat is expensive relative to any mass production thermostat, but this is a very hard part to reproduce. You can complain about availability or complain about price, but you’ll never find a $10 replacement for this application.
Thank you Michael.Re the Moss 434 156 bellows sleeve thermostat: .I looked hard, must have missed the .64 etc…but lots of text. 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 15mm 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 you say travels 8.382mm of sleeve travel. We know the Smiths has 9.5mm to 10mm: Looking not so good, 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 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. Thanks for your work, Nick
