Excellent research Mike!
Regards
David
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I added a big banner warning at the end, I’ll mention the pressure limitations again when I do the chapters on the S1 manifolds.
The big Easter egg was hidden in the Notes and Sources page:
Mike
For those pesky Americans, I would expand the Boiling Points of Working Fluids matrix to include a Fahrenheit column.
In the category of picking nits, un-underline the period at the end of the second lat .
Good stuff – looking forward to the next chapter!
Craig
Jag were already using Celsius dash gauges in the 1950s. Matching the story units to gauge scales has merit
Well, another month has flown by. Time to blow another half hour reading about thermostats! This month’s chapter discusses wax thermostats:
https://www.coolcatcorp.com/thermostats/Wax%20Thermostats.html
And to get a jump on next month, I’ve also published a page on the history of bypass systems:
https://www.coolcatcorp.com/thermostats/Bypass%20History.html
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Another nice reference article Mike, thank you. Interesting background history snippets as well.
My only query would be with the second sentence, which implies that higher compression inherently increases thermal load/running temps along with the power increase. I’d have omitted the reference to CR because, strictly-speaking, raising the CR improves thermal efficiency and produces less waste heat (hence cold-blooded frugal diesels).
Which reminds me I don’t recall ever changing a thermostat on any of the diesels I’ve owned and have no idea of their rating. I do recall blanking off parts of the radiator in winter…
Thanks Peter. I must have reread that fifty times and didn’t catch the error.
Maybe if you had changed your thermostat you wouldn’t have needed the cardboard 
. My exprience with Diesel is limited to Mercedes, which have cold-side thermostats rated at 180 or 185. Mercedes cars always tend to read hot on the gauge because inlet temperature is regulated, while outlet temperature is what it is. Causes a lot of unnecessary angst among owners.
3.8 L overheating.
I wanted to share this with fellow jag lovers thinking that surely this must’ve happened to someone else.
I’m now at the stage of my rebuild where I’m about ready to start driving it. This is a 1963 E-type coupe, with a 3.8 L engine.
I started the engine recently and found that it was overheating. The first thing I did was check the thermostat in hot water and it opened as expected. From there I started throwing money at it, new ‘Kool cat’ radiator and fan, then water pump and fan belt. I still watched the gauge rise until it boiled.
I decided to take a really hard look at the thermostat and figure out exactly what it did.
It doesn’t just open when the coolant flows on it, there is also a ring, or sleeve attached to it that is about 7/16 of an inch wide that moves as it opens.
When the engine is cold the coolant flows through the engine block, water pump and through a slot in the manifold where the thermostat is located, then back through the engine again. When the coolant is warm enough the thermostat opens and that ring slides over the slot and closes it off. That way coolant only flows from the radiator and cools the engine. That’s the way it’s supposed to work.
I took measurements from where the thermostat sits in the manifold to each side of the slot. I then took three thermostats, all of them new, put them in a pan of water and raised the temperature to 74°C, They all opened at the same time. I quickly took measurements of each one to see how far the ring had moved.
That’s when I realized the ring moved so far, it went right past the slot and continued until the slot was open again, allowing hot fluid to flow directly back into the engine again. That’s why it was boiling over!
Has anyone else run into this problem?
Thanks for your input.
Very nice paper on thermostats…thank you, this post is from my XK120 post…but relevant to the paper section on the bellows/sleeve thermostat topic…(I have found a few available: Peter, at ( “bitsn_pieces” on Ebay UK) has no more of the QH .but DOES have the AC bellows TF4…which is the equivalent…) note bene: the TF4 is the winter- 83C thermostat. But…one can drive it anytime however the operating temp will be a bit higher with the 83C full open thermostat, …but it is the fully functional bellows/sleeve thermostat which once fully open will maintain cooling with the 10C or so increase. The sleeve rises as the thermostat bellows expands and opens, the sleeve then closing the direct to engine path (no or little coolant to radiator) , while the bellows opens the coolant flow path to radiator. While this does mean less heat transfer from engine parts to the warmer coolant, there is an offset as a higher coolant temp thru the radiator means slightly more rapid cooling of the coolant. (the diff from coolant temp to ambient air temp is greater,) . A car with an otherwise clean cooling system will then run at about 85C-90C or so. Less leeway for traffic or really hot days…but otherwise OK. The winter thermostat recommended by Jaguar for the XK140, the C7105 had a temp of 83 to 86C. so similar. Yes…it’d be nice to have the 68 to 72C bellows/sleeve thermostat…The TF1 or TF3, if one can be found. This applies to the XK120-150 (and possibly some early XKE if prior to the cone/poppet thermostats used once pressure went above 4lb. )… As others say…the radiator cap must be no more than 4lb. for a bellows/sleeve type thermostat use. AND…to be correct for the XK 120-150 the bellows must have the sleeve. AC TF series has the sleeve, the TC series had no sleeve and is not correct. Nick
(which COOLS faster…very hot coffee…or coffee with cream that is less hot?)
I found a similar problem with the thermostat sold as correct for the 140…it is NOT…the block-off ring moves the wrong direction as it blocks the bypass when cold, but opens the bypass when hot. I WAS able to “fix” the problem by widening the block-off ring so that it now functions as it should. You MAY be able to effect a similar fix to your in-hand thermostat. The part no. of the modern (incorrect)140 stat is sold as a C3731/1. I do have a water rail from a later, HD carb set-up and it looks like my C3731/1 (UNmodified) would work with that newer-style water rail…which means it may work fine for your car.
Hi Alan Brown,I have been running my 3.8 for 28yrs with a regular thermostat and a restriction in the by pass hose.When I got my car I don’t think the sleeved thermostats were available.In a holding pattern now,if it aint broken don’t fix it!
Regards Gerry 62 Ots.
At least, don’t fix it till it IS broken!
The OP’s car IS broken…
…um…huh???
Mr. Brown’s car is broken(overheating).
it would seem the C3731/1.you had that did not fit, .was in actuality NOT a C3731/1 ??? Correct thermostats would be Smiths X43570/5 or X85025/72. Some vendor may sell under the C3731/1 number…but provide quite something else…Cross brand refs to the correct do exist in the AC TF1, TF2 and TF3, (TF4 winter) and QH…in the QT100 series.,.or QT200 winter. No modification to anything…they are correct…,.only the open spec temps vary, BTW the 140 for winter had the Smiths C7105, X43605/3, or later same but with # X85025/86 (TF4)
I’ll be getting to e-type manifolds shortly, I have no data on XK140. I do have a Mark 1 rail at hand, and it’s pretty much the same config as an S1 E 3.8.
The smiths sleeved stats were used by many manufacturers, and so the slots fall roughly in the same place… somewhere between 3/8 and 3/4” below the thermostat flange. It would be pretty weird if Jag decided to do something different and only for one model, but the location of the slot may vary within that range. What I have found is that rails and manifolds made by aftermarket vendors are only approximately right, which should be no surprise. The fact that the sleeve moves backwards is irrelevant. SNG3731 should work for any stock housing. Please post photos and measurements if you find this it not to be the case, and I’ll try to verify.
Moss motors makes a credible bellows unit that’s calibrated 74c. I’ve been fiddling with an adapter which would allow a standard double poppet stat to be used, but it’s a surprisingly tough problem.
I believe Nick is correct…the C3731/1 is an approximation of the original (at least, the one I bought turned out to be), made to service various models of Jag etc…so any specific car model may or may not be properly serviced by the C3731/1 I have. The biggest difference from the photos here, aside from the direction of movement, is the length of the sleeve…the originals being much longer than my replacement part. As I said, the part I have does appear to be workable for the early HD carbed set-up…C14651(IIRC) intake manifold, as used on the early Es, 150s and MK2.
Note that the bypass slot on the 140 set-up lies closer to the mounting surface of the thermo than it does on the later cars, and the slot is much wider…this is why any sleeve that moves AWAY from the mounting surface is problematic on the 140 in particular. I don’t have a 120 set-up to compare to but it is quite different in configuration.
the 120 and 140 thermostats “should be” interchangeable, although the fitment is in a different location. Jaguar Journal Sept and Nov 2016 has the article on thermostats by Bob Knijnenburg, which is available on line…bobine…cited earlier. Per this study, The bellows sleeve thermostats cited have top outer diameter of 54mm, sleeve diameter of 48mm, and sleeve height of 16mm. The 140 thermostat part number REMAINED C3731/1, Smiths X43570/5 and later just a part no change to the suffix to /28. the sleeve moves upward with the opening expansion of the bellows. The raised sleeve raises 9.5 to 10mm and thus closes the bypass, and opens flow to the radiator.(There is some minimal flow thru the closed thermostat to the radiator flow path to aid in a more rapid opening.)
Any vendor now…can list a thermostat with the Jaguar part number…but supply whatever thermostat they choose…often not necessarily the correct one. Others list a later type poppet/cone thermostat (no bellows, no sleeve) I suppose thinking…good enough. It is not,.
Nick