Ruby Radiator Water Level

[Steve Jones]

I fear you're getting misled by what happens in a modern, pressurised and pumped, system. Your Seven has a thermo-syphon, unpressurised system with no pump. As long as the water level at any time is above the radiator core all is well. By how much it is above is down to the level the engine/radiator sets for itself. All that happens when you top the radiator up above this level is that the excess is expelled via the overflow until the correct level is regained. If you then top it up the process is repeated. As a general rule, if, when cold, you poke your index finger down through the top of the filler neck and it just touches the water level then everything is as it should be. Calculations involving volume, power and measurements don't affect that in any way.

Steve

[Derek Sheldon]

U Just done 1300 miles to southern France and Switzerland in my 1938 Opal , full luggage , four blade fan ,   Very hot weather. Used 1/2 ltr of water and not sure that was really required

[Colin Morgan]

It says in the Vintage Alvis Manual (14.9) that the water capacity in a thermosyphon system was designed to provide a buffer against overheating (not necessarily boiling, but higher than desirable oil temperatures), which makes sense given the variable power requirements on the engine in normal driving before motorways.  The above calculation is intended to show that the quantity of water between low and high levels in the top tank, which turns out to be small, has little effect on this ability to ride out these variations - so trying to keep the top tank topped up for this purpose is pointless.

At the moment, I am adjusting from running a slightly leaky, heavily clogged radiator for many years.  It was from late 1938 and had a pressure relief valve fitted.  The older type replacement does not leak and runs at about 80 degrees instead of 90+. However, after noticing it was losing water by 'slosh', I wondered if this was usual.  If I could keep the level a bit higher I would, but from what is being said, this is not necessary - or even possible.  So, it seems the extra headroom in the top tank was provided to cope with the losses by 'slosh' - surprised Austin would accept the extra radiator height and brass just for this.  Thank you for all the replies.  Half a litre of water to cross half of Europe and back is impressive. 

Colin

[Bob Culver]

Pumped sytems continue to function with the water level somewhat below radiator fins but not thermo syhpon. As long as there is water in the block and head engines come to no harm despite reasonable boiling. With unsealed thermosyphon level needs regualr checking esp if unexpected or suspiciously prolonged boiling.