I took the above to my local garage to get it done. Turns out there was no thermostat in the car! The garage fitted one but from what I understand, it's not going to cure an overheating problem. 
They say the rad seems o.k but they suspect it's a water pump problem as the hose to the matrix, and the water within, is still cold. There was a new core plug fitted in Feb' 2016 and no engine blockages were picked up. I've been told that it's probably the rad- but I don't know. Are the rads easy to remove? Do I need to Jack the car up? I'm told by JEC members I can flush it out, upside down, with a hosepipe but ultimately I suppose it will need re-coring.
Thanks, Paul

Hi Paul,

Given the nature of the engineering when your car was built I believe it would be considerably easier than with a modern - eighties on - car. Fewer electronics for one thing and probably more space under the bonnet.

Frankly getting the radiator out should be reasonably straight forward and you can indeed flush it out with a hose pipe, but I agree with your engineer thats its more likely to be the water pump. It should also be a fairly simple task to remove and replace this too. The challenge will be to find a replacement.

Cheers,

Steve 

Had the radiator re-cored and they sandblasted the water pump; the nozzle being partially blocked, which seems to have cured the the problem.

Thanks, Paul

Hi Paul, I had a SIII Daimler Sovereign with the same XK engine and suffered the same problems.

Possible causes:

1. Water pump not pumping; see if belt slips, check pulley and belt, smears are telltale, eventually a toothed belt will slip a lot less than a smooth belt

2. Water not flowing evenly and freely within the engine block - gunk? deposits over the years? You need to "wash&rinse" the waterways (*)

3. Thermostat not opening properly; replace thermostat

4. Fan turning too slowly or has too few blades (It's warmer these times compared to 50 years ago); try an 8-blade fan from the S3 Sovereigns, and/or a "blowing" electric fan (Kenlowe etc.) on the front side of the radiator (very thin and will not show through the grille)

(*) You can also consider a "waterless" cooland liquid, which will work from -40°C to +140°C; this means no issues with antifreeze in the winter and safe operating temperatures up to and beyond "off the scale" readings of your temp gauge - it's worth considering...

Click here to read about waterless coolant

Cheers,

Maurizio, Rome, Italy

[note: same post as in your earlier thread, but chances are you've abandoned that and concentrating here]

I have a similar problem on my s-type. It’ll only overheat whilst waiting in long traffic queues. Once moving, the air flow cools engine again. Interestingly, my temp gauge never goes much above 70 when overheating? 

I wanted to know what size kenlowe fits the s-type?

neil