Cooling Woes by Larry {Doc} Jennings



Your cooling system was designed to operate under the conditions that existed at the time of its manufacture. Conditions may
include speed limit, type of fuel and coolant type. A cooling system needs to let the engine warm up and then keep it at whatever
temp is best for it's intended use. The system was designed for the best possible function at the lowest possible cost. It has the
capacity to maintain optimum operating temperature under normal conditions. The designer of the cooling system on, say, a '65
GTO would cringe at the thought of a 389 running on low octane fuel and retarded timing with the 33-year-old design, but I'll bet there
are more than a few cars running around like this. When these high horsepower, marginal cooling system cars heat up we just
increase the pressure on the system and we get by for awhile. All this really accomplishes is a higher boiling point, the temp will
still go up but the coolant won't boil until the heat overcomes the set pressure. Any liquid will absorb heat only until it reaches its
boiling point then it vaporizes. Each liquid has its own boiling point based on its chemical composition and the atmospheric
pressure. 

The radiator is a heat exchanger, as the coolant flows through it the heat is dissipated to the air that passes by the fins. If you turn
the heater on full blast on a hot day you will see the coolant temp drop. Funny thing is, many will pull out the thermostat hoping the
increased flow will cool better. Instead, this will speed up the flow to the point where no heat transfer occurs. The coolant needs to
circulate slowly enough to receive heat from the engine and to dissipate heat through the radiator. In the perfect system as the heat
builds in the engine the thermostat opens and closes to maintain a set temperature. This keeps you going down the road just
peachy. As the system becomes taxed, the thermostat just stays open. Your system is in trouble and there's no sign of it yet. No
telling how many cooling systems are running around on the edge and when they pop we think, it was fine and then POW. When in
truth it has been going bad for awhile. 

Speed limits put cooling systems to the test. I remember riding in my dad's '48 DeSoto; at 50 it ran normal, at 60 it warmed up but
was still OK, and at 70 it would move into the discomfort zone. Not overheated but hot. When towing a small travel trailer on a hot
day it would overheat on a hill no matter what speed we went. Water bags hung on the front bumper of all cars on trips in those
days. Now we expect older cars than that to go 80 all day and be just fine. I remember the owner's manual in my '64 Plymouth 426
warning the driver not to sustain high speed and that was when I could buy 101 octane on any corner. Now that we are contending
with air problems and will never be able to break away from gasoline, they will be constantly changing formulas. The burn rates of
these concoctions are very different. The advance rates are set for the burn rate set at the factory in what ever year the car was built.
It would be nice to be able to keep it that way. Could you imagine figuring out and re-curving the distributor every year or less? 

Additionally whenever you add horsepower you add heat. A little won't overcome the cooling system normally, but if the system isn't
that good in the first place it can be pushed to the boiling point. How often I've heard someone say, "all we changed was the cam".
A cam event change and, more importantly, static cam timing can change the heat output more than you can imagine unless you're
an engine builder. Exhaust can cool or heat your engine. More back pressure means more heat but reducing back pressure to
reduce heat will change where the engine makes its power. 

So it would seem that the very thing many are after, the original look, is the thing we need to change to keep our cool. If you're not
dealing with a concourse car, you can improve heat transfer capability by changing the radiator, adding an oil cooler, or increasing
the air-flow. Remember added louvers? They came about because lowered cars restricted airflow. An old 85-hp flatty thatís rebuilt as
stock with todayís technology now makes 100-hp or so. This will have increased the heat potential by about 18%. You can do
nothing to change the water jacket size, which controls the amount of coolant present in the engine. You might be able to slow the
coolant down with restriction or slow the water pump by changing pulley sizes to gather more heat but if thatís not enough it needs
more radiator or an oil cooler. Your engine cost plenty-try to keep that investment cool and healthy and it will save you money in the
long run. 

Larry Jennings
morsruby@peoplepc.com