Merlin Coolant Temperature Limits

[pbehn]

Eutectic system - Wikipedia

 

[Engineman]

Hi Dan,
There are very interesting points here. The Merlin, until the XII and XX developed in 1940, started with 100% Ethylene-Glycol cooling. This has a standard boiling point of 199 degrees C so it seems that, for example, a coolant limit of 120 degrees C was something of a mechanical or engine-system related problem, bearing in mind that maximum oil temperatures might be in the region of 130 degrees C in the return from cooling and lubricating the engine.
I can quote Alec Harvey-Bailey from his RRHT book "The Merlin in Perspective":
"Early Merlins used 100 per cent ethylene glycol cooling which allowed 135*C coolant temperature, but with the advent of the Merlin XII a major move was made to pressure water cooling using 30 per cent glycol as anti-freeze. The advantages of water as a cooling medium are considerable. With 135*C coolant temperature the mixture at 15 lb per square inch reduces the cylinder head metal temperature by some 30*C when compared with 100 per cent glycol"
So, at the same 135*C coolant outlet outlet temperature in a running engine, the water-glycol mixture removes more heat and achieves a 30*C lower operating temperature of the cylinder head metal.
Also, I think Sam Heron was quoted: "water is underrated as a coolant.."

Cheers

Eng