cooling and waterpump pulley misalignment problems

[cactusman]

Good points both David and Marek...money spent on the right part makes sense....as does money spent on beer :D

[MarekH]

Dear David,

If you don't have a problem, don't meddle with it is all I am saying.

The fundamental solution is that owners should understand how their cars work. If, as you suggest, you want a few degrees more headroom, just fit a 78'c thermostat instead of an 82'c thermostat. This will send water to the radiator 4'c "earlier" than before. There has been a lot of discussion about roughly the same topic with the v12 on the J-L forum periodically and it is obvious that most people don't understand what is going on.

I've no idea what your opening sentence is trying address - the problem being discussed is that there is "too much" bypass, not that it should be deleted. The function of the bypass is to heat the coolant quickly at startup to get the engine up to operating temperature. It is also, post 1970s, associated with dropping NO/NO2 emissions as these occur more at lower engine operating temperatures. After that, the dual route that the water can take is used as a means of keeping the minimum temperature as high as possible.

Ambient temperatures are pretty much a red herring - consider that the operating point of the engine may be set anywhere between 74'c and 88'c, all of which are well below cylinder temperatures.

Exhaust gas temperature at idle will be in the order of 250'c - i.e. not very high and it never gets lower than that on a running engine, but airflow and waterflow are factors:-

If you pull up too behind close to the car in front, then you are the architect of your own downfall.

Similarly, consider that at engine idle speed very little water is actually circulating as it is belt driven - again - this is your own fault if you don't periodically increase rpms.

Lastly, there won't be any airflow in stationary traffic. That's why cars have fans. Use them!

No one has even bothered mentioning that you can up the cooling capacity of the system by opening up the water flow through the heater matrix.

You have many tools at your disposal and understanding them first will get you a long way down that road.

It is only the radiator waterflow and airflow which will determine whether enough cooling will take place. When Jaguar had to pass more stringent tests in the Japanese market with the v12, their engineers decided to fit larger fans onto the cars - they were obliged to keep 88'c thermostats for emissions purposes so had even less headroom before overheating might set in. The cars didn't overheat.

Essentially, if despite not having 100% of the water go via the radiator route, the radiator manages to dissipate enough heat, then stop worrying.

kind regards
Marek

[mgcjag]

Photoes from Neal herridge...of his 4.2 stat housing, quite different bypass size to the 3.8
Dimensions for photo below Bore 50.1mm slot starts just 5.5mm from front face & is 3mm wide. there is also a 1mm deep c/bore in the front face.
This means the 3.8 stat would cover the slot when cold & leave it open when hot

[neal herridge]

I for one have not been running around like a headless chicken, the main reason for removing my stat was to get the dimensions for the 4.2 manifold.
As I said I have not had a problem with overheating, & I do know about all the things Marek has highlighted re cooling, but I agree with David, Jaguar designed the bypass slot to be covered by the thermostat & unless you use the bellows stat that pulls the ring forward it will not in a 4.2 engine even if you use the SNGB one which will work in the 3.8.
It goes with out saying that all the cooling system must be in good clean condition first.
I am not saying every thing Jaguar did was perfect & a lot of us on the forum like a bit of "upgrading" but the cars worked when first made & I find it odd that we may not be fitting the correct stats which must make things work even better.
As an engineer I don't agree with the if it ante broke don't fix it idea, the cooling system was designed to work in a way that using the wrong stat it is not.
Regards Neal
Steve I have emailed you the pictures.

[Heuer]

So far we have:

1. The bypass slot is 3mm wide and located at about 14mm depth, inner housing diameter is about 49.60mm - 3.8 (Ralph)
2. I got the same for slot size and location for '64 3.8 (top of slot @ 1/2" measured from cover mount surface. I got 1.95" for diameter, but there's a little corrosion in there. Depth of the hole is 1.8" - 3.8 (Eric)
3. Top of slot is .530" down from gasket surface; Bottom of slot is .640" down from gasket surface, slot is therefore .110" wide. Bottom of housing is 1.785" from gasket surface. Offset for thermostat is .035" deep. Inside diameter is 1.980". Offset for thermostat is .086 wide - 3.8 (Richard)
4. More of the same figures for my 63 FHC US car. Slot 4mm, set 13m inboard of the slightly recessed outer lip, internal diameter 50mm - 3.8 (Jonathan)
5. Slot 3.64mm wide, depth to slot 12.84mm, recess 0.9mm - 3.8 (Yves)
6. Bore 50.1mm, slot starts 5.5mm from front face & is 3mm wide. there is also a 1mm deep c/bore in the front face. - 4.2 (Neal)
7. Measurements from a 1966 4.2 engine number 7E5686-9 are as follows: Slot width .100 inch. Depth .500 inch to start of slot. Cavity ID 1.965 inch. (Gary)
8. Depth of machined recess 28 mm, both bores 49.5-50.0 mm; Face to slit 7 mm (4.2 log manifold) 6.5mm (Warneford 4.2 or 3.8 triple Weber). Slits 3 mm on SU 2.5mm on Weber. (Pete)

Neal - what is your engine number/year?

We need more 4.2 data.

[Heuer]

Looks like we have consensus on the 3.8's which are typically:

Bypass slot is 1/8? wide
Located at 1/2?depth
Inner housing diameter is 2?. A thermostat with a diameter of 1 7/8? would move freely and when open would successfully restrict flow into the bypass. The C3731/1* thermostat would work.



For the 4.2's looks like we have:

Bypass slot is 1/8? wide
Located at 7/32? or 1/4" depth
Inner housing diameter is 2?. A thermostat with a diameter of 1 7/8? would move freely and when open would successfully restrict flow into the bypass. No currently available thermostat would work. A NOS Smiths 85025/74 (wax pellet version) would work.



Notes:
1. I have changed the measurements to the nearest imperial fraction because that is how Jaguar would have set the machining
2. As the slot on the 4.2 manifold is higher up it would mean the by-pass would open quicker when the temperature dropped and close later than on the 3.8. Jaguar went to some trouble to make this change - they obviously knew more about what was going on than we do!

[ralphr1780]

I share the same angle of view expressed by Neal here above.
The S1 3.8 and 4.2 engines were designed with this specific bypass setup which provided "optimal" warm-up and cooling balance and efficiency in an original configuration. This was obviously a concern for Jaguar as the design changed from the XK to 3.8 to 4.2, and then to S2.
The pressure at the bypass and thermostat is identical, hence with a warm engine the flow through an open access bypass which slot represents some 20% of the total opened surface cannot be negligible and will have an impact on cooling performance of an original configuration.
Keen on learning more facts and figures!
Also, if any fellows around can comment:
Did Jaguar at any moment issue a service note for S1 engines recommending to change from a sleeve thermostat to a poppet? Or the other way around, a note recommending not to?
Seldom heard about S2 engines blowing head gaskets due to overheating, but heard about few 3.8 ones. Cases around here?

[Heuer]

This is the Service Bulletin Jaguar issued regarding the new "Quick-Lift" thermostat:



It used a wax capsule seeded with copper grains (increased rate of expansion and allowed control over operating temperature) to operate the sleeve and poppet. For some reason #C20766/2 was annotated as being "Tin Plated" to differentiate it from the version used by the saloons.

Anybody got a photo of an original or NOS C20766/2? It will look like this but be tin plated (simulated on the right) rather than brass:

[neal herridge]

David, my engine number is 7E2873-9 & its a 1965 car.
Also just as point of interest I have worked on a C-type & that does not have a bypass or a thermostat, as said before Jaguar only used this set up for racing. It backs up your thoughts re if Jaguar wanted to do away with the bypass set up to save money they had data from the race cars.
Neal.

[Polse7317]

I have now the sleeved thermostat (sngb c3731/1*) fitted on the motor.
The diameter is 47 mm , its housing is 50 mm , so the gap is 1.5 mm around .


First i tested it in hot water and after boiling: (temp opening indicated is 74C?)


The thermostat opened at+- 82C?



Then i tested in the motor , and the coolant has boiled after 40 min with the idle motor , a big fan in front the radiator ....


So , it's quite the same than with the "old" thermostat....
i am a little bit disapointed....!

[ralphr1780]

Yves, this is totally different from your previous thermostat! This one is at least restricting the flow through the bypass when opened while opening wide the flow to the radiator.
What is the ref of this one?

[Polse7317]

It's a SNG barratt one : C 3731/1*, but may be the 1.5 mm gap around let the coolant go a little or more ? in the by-pass . But i think i must have another problem...

[mgcjag]

Hi Yves.......sorry to hear that the new stat has not cured your overheating.....at least now you have what is probably the best thermostat option available.....you now need to look at other reasons for the overheating.....are your timing and carb fuel mixture ok

[Polse7317]

timing has been just checked by the mechanic for the first motor fire . But he is away far from here now , (SPAIN) . I have to solve the problems by myself for the moment.... and i am not mechanic . anyway i noticed one strange event: when i switch off the motor on the dash key, it continues to fire for 1 or 2 seconds and then stops with an "return explosion" in the carbs

[ralphr1780]

Yves, so if I understand you correctly: you have fitted the new thermostat and restarted the engine, and again the temperature started rising as before and reached boiling point. And when you turn off the engine, it still backfires for a couple of seconds.

Before restarting the engine, please ensure you have the timing set correctly, and particularly the firing order. Obviously there is something wrong with that.
With respect to the coolant liquid: are you measuring the quantity of liquid you are filling?

[Polse7317]

Hi Ralph, for the coolant i fill until +- 1 cm above the headertank bottom. I see the coolant flush easy when i open the filler cap and run the motor. (Surprisingly it flush from the right to the left side when i am in front of the radiator , but there are "two bottom" in the HT and the flush must turn Inside before going to the right exit to the radiator)
For the timing , i am not expert.... but i remembered that the mechanic had to change the order of the plugs in relation with the "123 electronic " manual , when he fired the engine for the first time. actually the engine starts very well and runs without any problem. (except over heating of course !)

[Heuer]

The running-on of the engine could be due to the fan generating a voltage as it keeps spinning when the ignition is off. Try running the engine disconnect the fan (pull off one wire) and then switch off. If the engine stops immediately you know the fan is a contributory factor.

[Polse7317]

Ok i'll try that tomorow .... another point interesting: i have a new headertank and its cap has 4 lbs opening pressure indicated . When i look at the cap " american original" which was on the car when i bought it, i read : 7 lbs ..... what is the good pressure ?

[Heuer]

Not really part of your current problem but the early cars had the cooling system pressurised to 4lb/sq". After about March 1963 the system was changed to 9lb/sq" with a different hose and cap: viewtopic.php?t=2006&postdays=0&postorder=asc&start=55

The 9lb/sq" cap would be correct for a post March 1963 car without the convoluted hose..

[Heuer]

Just received the Wat-Jag thermostat and machined housing to try. The Western Thompson thermostat is from a SII/SIII Land Rover (part number 532453) and is larger than the SNGB C3731/1*. This means the water outlet elbow requires machining with a recess of 2 1/8" diameter to a depth of 11/32". It does however have a sleeve that is 15mm deep and 48.5mm in diameter so will do a better job of closing the by-pass compared to the 10mm deep and 47mm diameter C3731/1*. On the positive side the thermostats are going to be available forever and they can be bought for ?4 or less!



Wat-Jag are now trading as Bronzegold Ltd and will be sharing a stand at Stoneleigh with Ken Jenkins. They will have a number of these kits on display if you want to take a look. Cost for thermostat, gasket and machining is ?54. If you are worried about modifying your own elbow SNGB can sell you a new one for about ?42.