Thermostat

Technical advice Q&A
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#1 Thermostat

Post by mgcjag » Wed Feb 17, 2016 11:04 am

Hi All....Just thought i would put up this post to aid anyone searching for info just on thermostats following on from discussions on another post here viewtopic.php?t=8355
It has come to light that when looking for a stat for your model there is some misleading info that could end up with you being supplied with and fitting the incorrect one.. this link
http://georgiajag.com/Documents/Thermostats.html
gives a very good description of thermostat related problems and shows the types of stats, so before replacing yours just make sure its correct for your model by understanding how the bypass mechanism works...usually early cars have a silt bypass and need a sleeve type stat, later cars have a round hole and use a stat with a disk on the bottom, but as we all know manifolds and engins can be changed so check your own requirements
Steve
1969 S2 2+2 & Building a C type replica

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#2

Post by 44DHR » Thu Feb 25, 2016 2:13 pm

As so many people have viewed the initial thread on Thermostats, I just thought I would share this additional information on Smiths Bellows type Thermostats and other alternatives written from the viewpoint of the XK 120, 140 and 150. It gives valuable information on these units.

http://www.bobine.nl/jaguar/02-engine/t ... 0-and-150/

I think this is quite comprehensive !!

The final comments on the later XK cooling systems are observant. Any thought to getting a replacement wax-type 74 degree bellows thermostats for 4.2 E types ? I was confused at first with reference and photos of the "Blanking Sleeve for non-sleeved thermostats" as if it somehow was attached to the the thermostat to move and block off the by-pass. As I understand it now, it just sits around the thermostat and does not move and blocks the by-pass at all times.

regards,

Dave
Dave Rose
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#3 Thermostat

Post by JimmyS » Sun Feb 28, 2016 7:12 pm

I'm have been reading the thread viewtopic.php?t=8355 with interest, particularly when the subject of thermostats came up. I have an inlet manifold / carburettor assembly without a thermostat awaiting refurbishment.

Image

Having read viewtopic.php?t=8262 I am even more confident I have a manifold suitable for a 4.2 E-Type.

Image

Image

I hope we are agreed that I have the correct manifold. Following David's request for more 4.2 data, here are the bore and by pass slot sizes on this particular item.

Image

Bore Ø1, 31/32" 49.848mm
Counter bore Ø2, 5/32" 54.877mm
Counter bore depth 1/32" 0.953mm

This is where things get awkward, as the slot depth from front face sizes differ from Neal Herridge's example. I have the slot starting at 15/32" 11.722mm down and 5/32" 3.899mm wide. My sizes were measured with a Digital Caliper in decimal Imperial mode, the recorded figures were converted to millimetres and also rounded to the nearest likely fractions.

I still have to figure out what thermostat to use....
Last edited by JimmyS on Tue Apr 17, 2018 11:11 am, edited 5 times in total.
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#4

Post by PeterCrespin » Sun Feb 28, 2016 8:40 pm

44DHR wrote:As so many people have viewed the initial thread on Thermostats, I just thought I would share this additional information on Smiths Bellows type Thermostats and other alternatives written from the viewpoint of the XK 120, 140 and 150. It gives valuable information on these units.

I think this is quite comprehensive !!
Flippin' eck! I've been 'scooped'! Bob has submitted this article for the May/June Jaguar Journal and I've just edited it. All JCNA members should cover their eyes :-)

I'll have to explain the meaning of 'embargo' to my Dutch contributor.
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#5

Post by Heuer » Mon Feb 29, 2016 12:07 pm

The article on the XK thermostats gives an interesting historical perspective but is of limited value to E-Type owners. The original alcohol bellows thermostats have not been available for many years and even if they were they could only be used effectively in those 3.8's fitted with a 4psi radiator cap. They also fail 'closed'. The sleeved thermostat sold by SNGB and others is not particularly effective because of its reduced diameter which does not seal the by-pass correctly but is better than nothing. The best solution is to use the #532453 or #596225 sleeved wax thermostat from a Land Rover SIIA/SIII because it is the correct sleeve diameter, works up to 9psi, 74C or 82C versions, fails 'open', readily available and low cost. It does however require the water outlet elbow to be machined with a 53.5 mm x 8.5 mm recess, something any engineering shop or lathe owner can easily do. Wat-Jag sell a kit comprising the thermostat, gasket and machined elbow (exchange) for ?50.

The #532453 thermostat can be used in all 3.8's. For the S1 4.2's the by-pass slot must be located at a depth of 9mm or more but as there seems to be a variance of between 6mm and 12mm, each manifold must be checked before proceeding.
Image

If you are not bothered about having a by-pass (so slower warm up time) you can fit a sleeve with a 3/16" bleed hole into the manifold or insert a brass bung with a 3/16" bleed hole into the by-pass hose. The sleeve is available from SNGB. I would not recommend either for road use!
Image

This is what happens with a single poppet thermostat fitted. A sleeved thermostat would close the by-pass when the poppet opens:
Image

This is the double poppet thermostat fitted to the S2 cars, useless on the S1 cars as the by-pass is on the side not at the bottom:
Image

It is not recommended you run your car with the wrong type of thermostat or leave it out completely. Without the thermostat the engine can take a long time to reach operating temperature which results in increased wear. Also the thermostat deliberately puts back pressure on the water pump because without it there can be cavitation which results in decreased flow and erosion of the water pump housing. Jaguar specified the thermostat for the entire XK engine production run - 1949 to 1992 - it is there for a reason!
Last edited by Heuer on Thu Mar 17, 2016 3:36 pm, edited 3 times in total.
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#6

Post by Heuer » Mon Feb 29, 2016 4:04 pm

44DHR wrote:As I understand it now, it just sits around the thermostat and does not move and blocks the by-pass at all times.
No! It would be unwise to fit both the sleeve and the thermostat because the latter requires a constant flow of water over it so it opens at the right time. By blocking the by-pass with that sleeve you are creating a pocket of almost stagnant water with the result the coolant temperature will go way over the top before the thermostat finally gets around to opening. The sleeve/no thermostat may be OK for racing but for normal road use the thermostat is essential by design to restrict the coolant flow, even when fully open. It puts back pressure on the water pump impeller to prevent cavitation which would reduce flow and erode the pump housing.
David Jones
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#7

Post by neal herridge » Sun Mar 06, 2016 4:45 pm

Update so far, I purchased a Landrover stat locally part No. 532453 to work out how to fit it into a 4.2. Problem is there is not enough metal a round the stat housing, it only has a wall thickness of about 4mm it would need boring out nearly 4mm bigger on the bore dia. reducing the wall thickness to just 2mm.
Next thought was to contact a firm which says their stat fits both 3.8 & 4.2 in total I made 5 phone calls to them over the course of which they told me that they had the correct stat as yes the other one would not fit.They said its the stat their mechanic fits to all 4.2 and they did not know why other firms had trouble supplying it, I ordered one it came Saturday & guess what its for a S2 not best please as I spent a long time going over what was needed.
Back to the drawing board, I can engineer a solution to the problem using the Landrover stat but it means turning down the stat OD after making a fixture to hold it boring out the housing by a small amount to give a step for the stat to sit in then making a ring to clamp the stat in place in the housing.
I does feel a bit over the top, & as David has said before I wonder what's in other S1 4.2 , just another thought I checked my rad cap & its a 7psi one so maybe I could use a bellows stat but its still not the correct solution for any one else .
Answers on a postcard please.
Neal.

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#8

Post by neal herridge » Wed Mar 09, 2016 9:26 am

Better news to report, after talking to the above firm they said they would contact Ken Jenkins (who I had already talked to ) & come up with an answer.
I have to say they have gone the extra mile on this one & put a lot of time into it the upshot being they think they have found a stat that can be modified to work with out to much trouble & I will have it to try next week.
Neal.

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#9

Post by mgcjag » Wed Mar 09, 2016 9:42 am

Great news Neal......nice to hear that you have stuck with it.... all the best Steve
Steve
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#10

Post by 44DHR » Wed Mar 09, 2016 10:12 am

Neal,

I have been following all these posts with interest and looked at Heuer's modified 3.8 thermostat cover pictured above. I have sent two new 4.2 thermostat covers, part number C23233 to WATJAG on Monday this week for them to modify to take their "special order" Thermostat for the "Series 1 4.2 E-Type, MK X & 420" as detailed on their web page. I measured them up before sending them and the ID of the outlet on the mounting face is 50mm, so I was was wondering how this could be achieved to both take the diameter out to 53.5mm as Heuer states, plus machine 8.5 mm deep without breaking through the outer surface.

Because WATJAG mention this thermostat would fit the other older Jaguars, it did not occur to me that they could be using the later type of Series 2 Thermostat with the bottom seal rather than the sliding bellow. I also sent them photos of my Warneford inlet manifold used for my Webers and exact details of measurements where the by-pass slot is and it's depth, so I trust they would not be using a Series 2 type. This Manifold appears identical to the standard 4.2 inlet manifold mounting and by-pass slot arrangement.

I will give them a ring in a minute to check they have my shiny new parts and that we are going down the correct route to provide me with modified housings to take a bellows wax thermostat to suit a Series 1 4.2 E type.

I must just add that this exercise is typical of me going off on a mission once I have been told a snippet of advice - when I was unaware of any issue before. I have driven my E type all over Europe and sat on the French Riviera on the Promenade des Anglais in Nice in the height of the summer sun absolutely cooking in the car, yet my car has never once overheated - with the Kenlowe merrily cutting in and out - all with the "wrong" thermostat !!
Dave Rose
1967 Series 1 4.2 FHC

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#11

Post by 44DHR » Wed Mar 09, 2016 2:42 pm

I spoke to WATJAG - firstly the owner and then he got Colin who does the machining to call me back. Both very helpful and Colin confirms that on the Series 1 4.2 E type, such as mine which uses the thermostat cover C23233, that this cover is not machined and it is a different thermostat which they specially order in which is machined to enable it to fit into the Inlet manifold. This would make sense as I was concerned that any machining on a C23233 would seriously reduce its overall sealing surface and break into the by-pass channel section. This is good news for others as you don't have to change or modify your original cover, just insert the modified thermostat. He confirmed that this is a bellows type thermostat that they modify.

So, I need not have sent my C23233 covers up for machining as stated on their web-site, but how I understand what Colin said is that the thermostat they will be supplying needs an area machining off to enable it to fit flush into the register in the inlet manifold thermostat mounting and reduce it's height as he said you could use it unmodified, but you would need several sealing gaskets to pad out the difference. He confirmed that the 3.8 uses a Land Rover thermostat and he implied that this 4.2 version was not - and if I heard him correctly, he said it had a Jaguar part number.

He has ordered in some of these 4.2 thermostats and when I get my two modified ones sent next week, I will post some photos of this modification.

regards,

Dave
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#12

Post by 64etype » Wed Mar 09, 2016 6:54 pm

I've been looking around for a small, normally open thermostat to place in the bypass hose...probably right at the bypass inlet pipe on the pump. So far, no luck in the search....moving to the motorcycle, offroad vehicle grouping next...
Eric

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#13

Post by Heuer » Wed Mar 09, 2016 11:40 pm

Great work Dave. Look forward to hearing and seeing how you get on.
David Jones
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#14

Post by 44DHR » Thu Mar 17, 2016 10:11 am

Update to the Great 4.2 Series 1 Bellows Thermostat Mystery.

Colin at WatJag has just called me to say they now have the thermostats that they modify for the 4.2 Series 1 E types and he will be at Stoneleigh on Sunday with some on display.

He is waiting to see Ken Jenkins tonight regarding an aspect of them, and then he will call me tomorrow to arrange to get my two off to me. As I won't see these now until after Stoneleigh, I want to advise Forum members going to Stoneleigh that they will be able to see the results there.

Colin explained that the 74 degree thermostats that they source are modified to the skirt and housing as both are too deep in their unmodified state. I wasn't aware that they also reduce the depth of the skirt, but this is good if they have the facility to do this to suit other manifolds employing the By-pass slot, such as my Warneford Weber manifold. I mentioned the interest this has generated on the E-Type Forum, so if you do visit the stand it would be good to mention this. He said the price of the unmodified Thermostat was around ?6.50 and once modified he hoped to be pricing them around ?12.50 plus VAT - which to me seems a bargain if this resolves our bellows supply issue.

I'm at the 74th Goodwood Members Meeting for both days this weekend, so can't make this Stoneleigh event, but regards to anyone can get there to check out this latest development.

regards,

Dave
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#15

Post by JimmyS » Thu Mar 17, 2016 2:33 pm

I still have to figure out what thermostat to use....
I purchased a Smiths thermostat 'X85025/86' to investigate the possibility of using one of them. I noticed it seemed to be snagging inside the manifold when I offered it up. You can see from this photo that where the internal machining stops, there is a slight ridge roughly 28mm down from the top face.

Image

Lifting sizes from the manifold and the Smiths thermostat, I modelled the situation in my CAD program to see what was going on. It seems to me I have the option of grinding some material away from the ridge inside the manifold or of reducing the height of the skirt (sleeve) that blocks the by pass slot.

Thermostat closed in simplified manifold...
Image

Closed Sectioned 1...
Image

Closed Sectioned 2...
Image

Opened...
Image

Opened Sectioned 1...
Image

Opened Sectioned 2...
Image

There seems to me to be evidence of scuffing in the manifold picture above, between the 3 & 6 o'clock position, where a previous thermostat has bottomed out. Can someone please tell me if the X85025/86 is just plain wrong for this application, other than being for winter use?

Regards,
Jim
Last edited by JimmyS on Tue Apr 17, 2018 11:16 am, edited 4 times in total.
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#16

Post by Heuer » Thu Mar 17, 2016 3:47 pm

Jim

It is the correct Smiths thermostat for the S1 cars, albeit the winter version. Looks like your manifold may not have been machined correctly. Is it the correct one for the 4.2 as it seems to have a cross pipe preventing the hosing from being deeper?

Dave

Thanks for the update. I will drop by the Wat-Jag stand and grab some photos and apologise to Colin as I have not yet fitted the replacement housing- holiday intervened!
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#17

Post by JimmyS » Thu Mar 17, 2016 4:05 pm

Is it the correct one for the 4.2 as it seems to have a cross pipe preventing the housing from being deeper?
Thanks David, I did wonder if I had the correct manifold but having read viewtopic.php?t=8262 I am confident that I do. The cross pipe you refer to is the inlet route to the number 6 cylinder if I understand you correctly. It looks like I need to tidy the ridge off then and take things from there.

Regards,
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#18

Post by 44DHR » Fri Mar 18, 2016 9:14 am

Not meaning to make this a long running saga - and mighty impressive CAD diagrams by JimmyS by the way.

I thought - or I'm expecting - my modified WatJag thermostat to work in a different way to JimmyS's representations - in that I think when cold the sleeve will be shut up against the mounting face to allow coolant to pass out through the by-pass slot from inside the manifold. When the coolant warms up, the sleeve will move down to open the main part of the thermostat - i.e. into the manifold and cover the by-pass slot.

If I understand it correctly, Colin is modifying their thermostats so he can shorten the present sleeve length to ensure it is clear of the slot when cold and then as it moves down to cover the slot it is not too long to hit the internal ridge inside the manifold. These are the photos that I sent to Colin of my manifold together with detailed dimensions of what I am seeking.

Image

Image

Image

Once Heuer can get some photos at Stoneleigh or I get my modified thermostats and take some photos to show you, hopefully all will become clear.

Cheers,

Dave
Last edited by 44DHR on Fri Aug 04, 2017 3:52 pm, edited 1 time in total.
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#19

Post by Heuer » Fri Mar 18, 2016 11:39 am

Dave

The thermostat Jim has bought is the original bellows design which works in the opposite way to the modern one Wat-jag are supplying.
David Jones
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#20

Post by ralphr1780 » Fri Mar 18, 2016 12:58 pm

I may be wrong, but both thermostat housings of Jim and Dave seem to have different characteristics from the ones which were already illustrated in previous discussions. Difficult to keep track with obviously so many manifold variations.
Ralph
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