» The engine, hoses and the ground beneath
the vehicle should be checked regularly for
wet areas that may indicate a coolant leak.
Photo courtesy of Navistar
May 2018 | VehicleServicePros.com 25
Water pump - Driven by a belt, the water pump
circulates coolant throughout the engine via
pipes and hoses. Th e coolant is pumped through
the water jacket, which is the space surrounding
the cylinders. Heat is transferred from the
cylinder heads and sleeves to the coolant, which
then circulates back to the radiator.
Radiator - “Th e radiator specifi cally applies to
the device that takes heat out of the coolant
and ejects that heat into the air,” Navistar’s
Nachtman says. “Air fl ows through the grille
on the front of the vehicle, it goes through the
radiator which is fi lled with hot coolant, the
heat is transferred to the air and the coolant is
cooled. Th en it goes back into the engine and
the cycle repeats.”
Fan - Th e fan sits behind the radiator and works
to pull air through in order to remove heat from
the coolant. It is driven by a fan clutch, which
dictates when the fan is on or off . Depending on
the effi ciency of the cooling system, the ambient
temperature, how fast the vehicle is moving and
other factors, the fan may not always need to
be running in order for the radiator to allow for
eff ective cooling of the coolant.
Th ermostat - While smaller gasoline engines
use only one thermostat, larger diesel engines
typically have two. “Th ermostats open to allow
more coolant to go through if the engine is
operating hot and needs to be cooled off ,”
Nachtman says.
On modern vehicles, cooling systems are not
limited to cooling only the engine. Th ey also
serve to regulate temperature in a variety of other
systems on the vehicle.
“Th ere’s an oil cooler, so coolant regulates the
oil temperature,” Nachtman says. “Coolant fl ows
through the exhaust gas recirculation (EGR) cooler.
It also fl ows through the EGR valve and the
turbocharger … Certain applications may have a
transmission oil cooler, or a power steering cooler
- those all use coolant as well.”
Not just for cooling
While coolant is eff ective at removing heat from
the engine and other components, it also serves
a dual purpose by providing heat where needed.
Take, for instance, the heat in the cab of a vehicle.
A heat exchanger (any device that takes heat
from one element and transfers it to another) takes
heat from the cooling system’s coolant and transfers
it to the air in the HVAC system, which blows
through the vents into the cab.
“Coolant is also used to warm up the DEF (diesel
exhaust fl uid),” Navistar’s Nachtman says. “In the
winter time when it’s cold enough, DEF will freeze
solid, and coolant is used to warm up and thaw
the DEF in the DEF tanks.”
Another way that coolant is used for heat is
in-transit heat in trailers. During colder winter
months, in-transit heat systems allow hot coolant
from the truck’s cooling system to be circulated
through the interior of the trailer to keep the cargo
from freezing. Th e coolant then circulates back
into the truck’s engine.
“Some customers will also order shut-off valves
so that coolant only fl ows through the in-transit
heat system when they choose,” Nachtman adds.
Keeping up with
cooling technology
Ever since internal combustion engines have
been using water cooling systems, the basic
principles of the system have remained the
same. However, as demand and regulation have
required, the technology used in these systems
has changed in order to make them more effi -
cient. Emission requirements set by the EPA were
enforced beginning in 2007 and 2010. Th ese
requirements changed how heavy duty diesel
engines operate and, in turn, how effi ciently
cooling systems need to function.
“Since 2007, diesel engine emission technology
has changed,” says Brian Daniels, manager
of powertrain and component product marketing
at Detroit Diesel. “As a result, newer engines
Fleets can reduce
downtime by performing
proper cooling system
maintenance, inspection
and testing.
/VehicleServicePros.com
