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Classic S Type Overheating Problem


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My temperature gauge goes up to around 80% on journeys.  The fan seems to be working ok and there is plenty of coolant in the system.  I've been advised to check the temp of the water in the rad with a thermometer to see if the gauge is working.  The engine has had a lot of work done so I don't think there's anything major going on, but the rad feels a bit furred up in the neck.


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  • 1 year later...

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


Maurizio, Rome, Italy

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  • 2 weeks later...

 Thank you Maurizio, you’re a gent. At one garage, people working on the car found that there was no thermostat in there and replaced it.  I think it was taken out to resolve an earlier overheating problem. I have had the radiator re-cored and a new cap put on and although the bottom half of the radiator cowl is missing I don’t think there is a coolant flow problem .

You have given me some good points to consider here, but I think it might be something as simple as having the thermometer re-calibrated, along with some of the other instruments.  It’s not now boiling over like it was

Thanks again, Paul



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  • 1 month later...

I have a 1948 MK V that had overheating problems. A friend suggested using Evapo-rust. I drained the coolant, flushed the system twice with water, then filled the system with Evapo-rust that I ordered from Home Depot,  $80 for a 5gal pail. I ran this for a month using the car every day. Each day I noticed the gauge being lower. Once it was running normal, I drained the Evapo-rust back into its pail to use later in another vehicle. I then flushed twice again today and filled with antifreeze. It works great, No overheating now at all! Evapo-rust does not eat aluminum, gaskets or effect the water pump.

 I highly recommend this product.

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