The Risks of Cooling Down

Engineering is a constant battle of risk versus reward.  How much are you willing to challenge your equipment in order to gain speed?

Speed is at the heart of the new ‘knockout’ qualifying.  The new format has made Friday afternoons much more interesting; however, it also raised a new series of issues and challenges for NASCAR and the teams.

NASCAR wanted to limit the types of changes that can be made to the cars during the qualifying process.  One of their limitations is that the hood cannot be opened, which precluded the use of cool-down units.

Without the cool-down units, teams were having their drivers run laps at extremely slow speeds to give the engine time to cool down. A number of drivers raised concerns about the safety of cars doing 40 mph on the same track as others running 180 mph.

NASCAR announced last Tuesday that teams would be able to use one cool-down unit under the following conditions:

• One unit may be used
• The unit must be connected through either the left- or right-side hood flap/cowl flap
• The hood may not be opened
• Generators may not be plugged in
• No cool-down laps allowed

Cooling down the engine is critical to getting that fast lap. Andy Randoph, Engine Technical Director with Earnhardt Childress Racing Engines, tells me that an unrestricted Cup engine loses almost two horsepower for every 10° Fahrenheit of water temperature increase.  Cool engines are fast engines.

An engine cool-down unit is a big box (about 2 ft x 2ft x 3ft) with a reservoir for 12-15 gallons of water and (often) ice.  The cool-down unit is hooked up to the radiator system and pumps cold water through the engine cooling system.  An engine may be about 280 F when the driver pulls it off the track onto Pit Road. Most cool-down systems boast that they can cool an engine to 50 or 60 degrees Fahrenheit in about five minutes.

Cooling an engine from 280 °F to 200 °F represents a gain of sixteen horsepower.

With very few exceptions (i.e. water), heating a material causes it to expand.  Cooling it makes it contract.  We often model atomic bonds as having the atoms connected by springs.  The hotter the temperature, the more the atoms move. The result is that the material actually gets bigger when it gets warmer.

But different materials expand and contract at different rates. For example, metal changes size much faster than glass. Running  a glass jar with a metal lid under warm water makes the lid expand more than the glass and lets you remove the lid.

Cool-down units cool the engine quickly  and that opens up a lot of possible problems because the cooling doesn’t happen uniformly.  There are a lot of different types of materials in an engine.  For starters, the cylinder head is made of aluminum and the engine block of cast iron.   When you cool the engine quickly, the differences in contraction rates create relative motion at the head gasket interface – where the head and the block meet.  Fasteners that once were tight can loosen up.

A second concern is that it is very difficult to maintain water level when using a cool-down unit.  The motivation for not allowing teams to open the hood during qualifying is to limit the types of modifications they can make to the car.  You’d have to position an official on each car if you let teams open the hoods.  Teams are going to have to be careful in how they do the cool-down procedure to make sure that they leave the car with enough water in the radiator system.

I know Chad Knaus told Dave Moody that he didn’t expect any problems with using cool-down units. A key trait of crew chiefs is optimism.  Changing a tire should be a routine act as well, but how many times have teams lost races because of loose or missing lug nuts? There are going to be situations in which a team, having just been knocked out of the top 12 with two minutes left in the session, are going to rush to cool the engine down and make another lap – and do it too quickly and have engine problems later.

As Andy Randolph told me, this is a classic case of risk/reward.  How much are you willing to chance damaging the engine for the race in an attempt to secure a good qualifying spot?