Excess anti freeze kills Landcruiser head gasket? - Antifreeze mixtures - long

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"I always understood that the anti freeze aided with the cooling."
Hi Julian and the list,

Complicated but best heat removal in thermodynamic terms is from water with
a wetting agent, then water only, then a water/antifreeze mix, as usual the
real world is a little different and antifreeze does help in the coolant.
The short answer is of course always use the recommended coolant mix and
change it as specified. Ethylene glycol used in antifreeze is acidic, so
corrosion inhibitors are added to antifreeze mixtures. These inhibitors can
become exhausted hence the reason antifreeze needs changing, the fact the
tester shows it is still "working" doesn=92t mean it shouldn't be changed.
Measuring the pH level can show if it is still OK but flushing and changing
the coolant when recommended is the best route. Always maintain the correct
mixture of antifreeze and water.
In case anyone reading the list isn't sure what is being discussed more
specifically but is interested I will try to explain (and probably get
something wrong). None of this is meant to suggest that Neill's head gasket
was killed by too much antifreeze, from the text below you will see that too
much antifreeze (100%) used in winter would probable still work ok but the
coolant temperature might be a bit higher.
Ethelene glycol has a specific heat capacity that is about 60% of water.
Specific heat capacity is the amount of energy required to heat particular
mass by one degree, units are not important as we as interested in ratios,
(good thing to because so many different units are used), basically (don't
try this) if 1 litre of water is heated for 1 minute and heats up by 40 deg,
1 litre of neat antifreeze with the same heating will heat up by 66 deg. (40
divided by 0.6) The more heat needed to warm the material up the more heat
it will be able carry away to the radiator.
(I think actually the figure for the pure antifreeze heated will be a little
different because the antifreeze is denser, probably about 60 deg.)
Different mixes of water and antifreeze have varying specific heat
capacities but they are all less than just water. All this means you need to
move more antifreeze around to do the same job as water.
Some confusion over antifreeze comes about because Ethylene glycol has a
higher boiling temp than water. This higher boiling point is the reason why
one of the first cooling uses was in aeroplanes, it allowed planes to have
smaller radiators with less coolant. Using 100% antifreeze in a system
designed for a water/antifreeze mix will reduced cooling capability and
probably increase operating temperatures, a higher capacity pump might be
required and the more viscous nature of 100% ethylene glycol would cause
problems, no real gain unless your cooling system is designed to operate at
high temperatures (or low pressures).
So although ethylene glycol can work at higher operating temperatures most
engines don't operate much above 90 to 105 deg C, so the coolant doesn't
need the higher boiling temperature. The complication comes about because
the higher boiling temperature is actually useful in cars even though the
coolant system temperature is below the boiling point of water (or water at
15 psi perssure). The higher boiling temperature for the coolant with
antifreeze reduces localised boiling which occurs normally inside the engine
where the coolant comes into contact with hot surfaces, head, cylinders etc.
When the coolant boils and becomes gas the bubbles of gas insulate the hot
surface from the coolant, because antifreeze reduces the local gassing it
improves the cooling system performance. The higher boiling temperature
might also help if the cooling system is on the limit, stationary in traffic
etc but the higher temperatures seen then are ones you want to avoid if
possible, not promote.
"Wetting agents" were mentioned above, these work by making the gas bubbles
smaller so they disperse quicker, so improving the performance of the system
but without reducing the heat carrying capability of the coolant, hence the
reason water with a wetting agent is better than antifreeze. (I think
wetting agents also act as corrosion inhibitors.) There might be an issue
with just using a wetting agent in above freezing temperatures, probably
just myth but some people say if you have air conditioning and water in the
heater matrix can freeze.
Hope someone is interested in all this, just happen to have been looking at
the cooling on my 2F engine and thinking about how an electric circulation
pump might work, writing it down has been useful to me at least!
Malcolm Bagley
Stafford, UK
1975 FJ45 Pickup (in work)
1976 FJ45 Pickup (next one)
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