Jim:
<<<snip>>>
They still recommend the same standards of mixture. Do they use a
longer lasting corrosion inhibitor or what?
<<<Snip>>>
Maybe, but you've also changed the cooling system from dissimilar
materials (cast blocks with aluminum heads) to one of just one material,
aluminum, instead of the all cast iron of 30 years ago.
The main reason for the 50/50 mix TODAY is to control the boiling point
of the coolant. It has nothing to do with the quantity of additives.
Modern cars must run hotter to control emissions. Anti-freeze raises
the boiling point. Older cars using water and running at a coolant
temperture of 175d F have a margin of 37d F before boiling. Many modern
engines use a 190d F or 195d F thermostats. With straight water and a
15 lb. radiator cap the boiling point is 230d F. (Notice the 220d F
STABILIZED temp in one of the charts I referenced.) Antifreeze
increases that safety margin more. So that's the main reason why they
specify the 50/50 mixture. The hotter temps are also the reason for the
pressurized systems. Notice that car makers keep raising the pressures
in the systems rather than increasing the antifreeze ratio to control
boiling.
In regards to the 5 year life, I have read that the additives for
corrosion have evolved over the years taking into account the more
extensive use of aluminum in engines.
Consider the situation 35 or so years ago. Except for the exotics, AMC's
aluminum block 6, or very early Ford flat head V8s, most engines were
all cast iron. In other words there were no dissimilar metals in the
cooling system. So the additives only need to protect against rust.
(BTW, Ford discontinued those early aluminum heads after a few years due
to corrosion problems.)
Then came the modern aluminum heads and water pumps. This is probably
the worst condition because you have about 1/2 of each type of metal in
the cooling system. Thus galvanic and electrolysis corrosion could be
very active besides rust of the iron components. So the additives get
used up faster trying to protect the system.
With your all aluminum system there are again no (or few) dissimilar
materials. The only additives needed are to protect the aluminum and
electrolysis is at a minimum. Therefore the protective additives get
used up more slowly.
Cooling systems were designed for the coolant available at the time they
were designed. Anybody remember when alcohol used to be used for
anti-freeze? England doesn't have the real cold that we have in the
northern plains. Cooling systems for the T types and MGA were suitable
for England's milder climate and WATER coolant or low antifreeze mixes.
Glycol was very expensive in the 50's so minimal amounts were used IF
NEEDED. The 1956 Montgomery Wards catalog lists THEIR BRAND at $2.19 a
gallon plus shipping while men's denim's (blue jeans) are as low as
$1.66. And, they probably had the cheapest price for antifreeze
available. The TD shop manual says: "If ... anti-freeze mixture is in
use, the water should be drained into a suitable clean container and
kept for future use. ... Avoid over-filling when anti-freeze is in use,
to prevent unnecessary loss on expansion." Nothing is mentioned about
quantity of use. The MGA twin cam shop manual lists anti-freeze needed
in three steps down to 35 degrees of frost. That's minus 3d F and a tad
over a 25% anti-freeze mixture. Again cost was being considered.
Today, the radiator and cooling system is designed for a 50/50 mix and
the radiator, pump, and coolant flow are sized appropriately.
Blake
P.S. Pure anti-freeze has a specific heat of 0.675 compared to waters
1.008 at 212d F.
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