> However, adding glycol to water has an adverse effect on heat
>transfer so engine cooling will be adversely affected by having higher
>glycol concentration. In other words, keeping the coolant mixture from
>boiling is not the same as providing more efficient cooling for the engine.
>So, one must ask: is the cooling problem indicated by high coolant
>temperature (or boiling) or by high cylinder head or oil temperature?
>Rob Housman
Rob
In the early Rotax 912 installation notes 100% glycol was specified.
Perhaps to prevent boiling at cylinder head hot spots, (my guess, we
weren't told the reason). Spot boiling would also reduce heat transfer,
vapour conducts heat worse than liquid.
We soon found that diluting the coolant to 75% glycol had a big effect on
cooling. Much better. Eventually Rotax and Europa suggested 50% glycol but
the effect on boiling point was not discussed AFAIK. Max CHT was still
specified at 150 deg C. Way above the boiling point of the coolant.
PFA now require coolant temp to be measured rather than CHT. Very
sensible,IMHO but please note the boiling point, 115deg C or 130deg at 1
bar overpressure, (the relief valve is set at 1 bar)
Graham
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