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Old 1st April 2016, 16:15
Mike Mike is offline
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Default Over heating

Hi Tim

Based on your photos on flickr, and my own very similar experience, I suspect your problem may have more to do with the positioning of your expansion tank relative to the top of your radiator.

My M50 did just the same on my first proper run. When I did some research I determined that water expands 10% by volume from 4 degrees C to 110 degrees C (the boiling point is raised by increasing the pressure in the cooling system). So, given that the cooling system held around 5 litres there will be at least half a litre forced out as the cooling system reaches maximum temperature.

I only cured mine by adding a tank with a 1 litre capacity (anything less resulted in water being boiled off, and then the system sucked air back in as it cooled) and mounting it on top of the front bulkhead - the highest point under the bonnet - (and still only just above the top of my radiator).

From your flickr site I would suggest your header tank is mounted too low.

If you want to experiment to prove the point, add in a little more feed pipe to allow your tank to temporarily fix above your bonnet line.
Then take your car for a run. You will lose some coolant as it expands, so make sure you have an overflow taking it below the chassis, and allow the engine to reach maximum temperature. When it cools down to cold, the header tank should still be half full.

Hope this helps - let me know how you get on


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