McLaren’s Dual Cooling Circuits Demystified

The cooling circuit in most sports cars are fairly straightforward and consistent.  For high strung turbocharged cars, not only do you need to control engine thermals  (e.g. coolant, oil), but also the high intake air temps from turbochargers.  Turbochargers can spin upwards of 200,000 rpms!  As you can imagine, this creates a LOT of heat.

Without any intervention, intake air temps would soar past 200 deg F.  Since hotter air is less dense, it contains less (densely packed) oxygen particles. Simply put, less oxygen in your intake stroke, means less power at the wheels.

For this reason, we need some form of intercooling to remove some of the heat and increase efficiency.  The standard option for OEMs is air-to-air intercooling (e.g. Porsche 911 Turbo).  Air-to-air intercooling has the added benefit of being lightweight (little plumbing, no pumps) and working very well at high speed.  The negatives to air-to-air intercooling is heat soak when no air is moving over the intercooler fins; idle or low speeds.  The placement of the intercoolers are also very limiting when designing the car aerodynamics since these need to be in direct airflow.

McLaren chose a different route on the P11, P12, P13 and P14; water-to-air intercoolers.  Water-to-air intercoolers have the benefit of providing consistent intercooler temps, regardless of vehicle speed. They also can be tucked away under body panels and still work. The negative is more plumbing, since you now need “heat exchangers” to remove the heat from the water intercooler circuit.

The end result from McLaren is a total of 6 radiators and two coolant pumps* (2 water radiators, 2 intercoolers, 2 heat exchangers); not counting the oil, clutch and trans coolers!