Coolant flow

Tech Talk #78 – The Big Chill: How to Avoid an Engine Meltdown

This is from tech talk #78.

"Why are drag racing engines prone to meltdown? We’ve all watched NASCAR engines run 600 miles at wide-open throttle on a sweltering summer day without problems. At the Bonneville Salt Flats, land speed record racers run flat-out for miles at maximum power. And yet a dedicated drag race car probably wouldn’t last a minute under those conditions.

The answer is in the math. One gallon of gasoline contains roughly 120,000 British Thermal Units (BTU) of heating value, enough energy to raise the temperature of 1,000 pounds of water by 120 degrees. A typical internal combustion engine converts only about 25 percent of the fuel’s energy into useful work (accelerating the car). The rest is turned into waste heat or consumed by mechanical friction. Approximately 30 percent of this waste heat must be dissipated by the engine’s cooling and lubrication systems. So if a drag race engine burns one gallon of gas in the course of staging, burnout, and a quarter-mile run, potentially more than 36,000 BTUs have been dumped into a cooling system with a capacity of only a few gallons of water.

Most drag race cooling systems are utterly inadequate to dissipate such staggering heat. Drag race cars typically use tiny radiators (or sometimes no radiator at all), low-volume electric water pumps, and inefficient fans that simply can’t cope. It’s more accurate to think of these components as “cool down” systems rather than cooling systems, since their chief purpose is to reduce coolant temperature after a run.

A true cooling system would require a massive radiator, a high-volume water pump, and huge fan to balance the input and output of heat. Look at the size of the radiator that’s required to cool a 500-horsepower engine operating continuously in a diesel-powered commercial truck– it’s enormous. Even the cooling systems in passenger cars and light trucks are rarely able to keep up with the heat gain when the engine is run at continuous peak power. That’s why the temperature gauge in my Suburban quickly heads for “H” when I’m towing up a grade."