Keeping Your Cool in a Tiger

An Article by Dan Walters
September, 2001

Page 5

Antifreeze Final Exam:

....So, you have just installed a "rodded out" used or a new radiator and tightened all the hose clamps and closed the drain valve. Are you about to add a 50/50 mix of water and antifreeze? What do you know about antifreeze? Where did you learn about antifreeze? Is your Sunbeam subjected to sub-freezing temperatures? If the answer to this last question is no, maybe antifreeze is not the best coolant to run in your car.

.....Test your knowledge of antifreeze:

Given: A 50/50 mix of water and antifreeze-

-Lets your cooling system run _________ degrees hotter (then straight water) before boiling over.
-protects your car from freezing down to __________ degrees.
-protects your cooling system from corrosion for __________ months.-is ________________ to humans and _____________ to small animals.
-causes your cooling system to run about __________ degrees _______ then straight water in the cooling system.
-causes your cooling system to take about _________% of the time to reach operating temperature then with straight water in the cooling system.
-is made of ______________ ________________ .
-is _______

OK, No fair reading on 'till you've filled out the blanks!

Answers You Already Knew (?):

.....Antifreeze was developed as a year-round coolant to replace alcohol used in cold weather and water in hot weather. Alcohol as a coolant is good down to about -125F but has a problem of a low boiling point (about 180F). Water as a coolant has some good qualities, it conducts heat well and the temperature goes up quickly as heat energy is put into it (known as specific heat). Water has two problems, it freezes and corrodes metal.

.....Standard automotive antifreeze is Ethylene Glycol (#7), part of the Glycol family which includes Propylene Glycol (used in many things including cosmetics and newer antifreeze) and Polyglycol (brake fluid). Glycol is made of GLYCerin and alcohOL. Antifreeze is a compromise with a wide temperature range (-32F (#2) to 226F ) but less desirable qualities such as lower heat conduction and lower specific heat than water. A 50/50 mix of Ethylene Glycol and water conducts heat about 54% as well as water, and has a specific heat of 88% of water. You may think that antifreeze cools better than water because the coolant takes longer to warm up (about 112% #6) than straight water. But antifreeze absorbs more heat energy than water before the temperature goes up. Add to that the poor heat conduction and It's not uncommon to see coolant temperatures 5-10F degrees hotter (#5) than with straight water.

.....Environmental concerns have brought about the use of Propylene Glycol as antifreeze. Ethylene Glycol is toxic to humans and poisonous to small animals (#4), propylene Glycol is inherently safe to humans and animals, only the additives in propylene Glycol antifreeze are a small problem. Propylene Glycol is less desirable then ethylene Glycol because it has a slightly higher freezing point and slightly lower boiling point (50/50 water mix).

.....If your car is not subjected to freezing temperatures, you gain two things with antifreeze: about 14 degrees (#1) higher boiling point and about 12 months (#3) corrosion protection. However, you lose some efficiency of the cooling system. The amount of raised boiling point is almost negated by the lost efficiency. Consider that the boiling point is raised 3 degrees for every pound of pressure you add to the cooling system. A 5 pound pressure increase with straight water would equal the antifreeze boiling point without the loss of efficiency. Note, cooling systems must be in good shape before adding pressure. Typical weak points are heater cores and header/filler tanks. Early Tigers had 13 lb pressure caps and late Tigers had 9 lb pressure caps as standard.

.....Speaking of pressure, with straight water and a standard 13 pound pressure cap the boiling point is 212 + (13*3) =251 degrees F. Antifreeze would add 14 degrees for a total of 265. Also consider that the pressure inside the cooling system is not constant, it varies with location. The location of the radiator cap determines what pressure the cap sees. Pressure will change just by the temperature alone (heating by the engine, cooling by the radiator) and also by changes in flow (restriction of the thermostat, suction of the water pump). It was determined long ago that a restriction at the coolant outlet of the head was beneficial, especially in extreme conditions. By raising the pressure (and boiling point) of the coolant in the head, localized hot spots (typically around the exhaust valves) were cooled better because of reduced localized boiling.

.....The only thing left is corrosion protection. With the recent addition of coolant additives that help water cool better by reducing surface tension and increase heat conduction along with corrosion protection, antifreeze is left out in the cold as far as usefulness in the cooling system! In other words, antifreeze is overrated (#8).