What is the reason for the new 5.7 liter
Hemi R/T engine having 14.5 quart
capacity cooling systems and using a
203°F thermostat? The capacity seems
too small for an advertised 370 HP
engine. The 203°F thermostat keeps the
engine close to the overheating range.
The owner’s manual contains many warnings
against letting the engine overheat.
I want my 2017 Charger R/T Hemi
engine to last beyond the warranty
period. I first noticed this issue at a
dragstrip test session for my brother’s
Charger 440 6-Pack automatic. They all
worked well, for many years, using 160°F
thermostats and heavy duty cooling systems.
My Chilton manual lists the 1958392 Hemi as a 25 quart cooling system.
The original 2003-2008 Truck Hemi 5.7
had an 18.7 quart cooling system. What
is the explanation for the new car Hemi
cooling systems being so small?
First off, at sea level, assuming an 18 PSi
pressure cap, plain water boils at 255°
F. So you’d have to get the engine more
than 50° hotter than the 203° thermostat
set point to worry about boil-over. And a
50/50 mix of water and ethylene glycol
raises that boil point significantly (+11° F.).
So, unless there’s a leak, it will never boil
over and, even assuming a total loss of
pressure, there’s still ample overhead to
get down the road.
You are confusing cooling system
capacity with the heat rejection ability of
the radiator. Today’s aluminum units are
very efficient, as are the fan systems. The
hotter the coolant, the greater the ▵t. In
other words, the greater the difference
between the coolant temp and the ambient
air temp, the more heat (BTUs or calories)
the cooling system can remove from
the coolant. The water jackets are much
smaller, allowing much quicker warmup,
therefore better fuel economy, less ring/
cylinder wall wear, fewer emissions, etc. It
is a win-win.
Think back 30–40 years. In the summer,
it was common, especially in mountainous
areas, to see a car on the side of the
road, or at a service station, stopped with
boil-over. That’s extremely rare today.
With reasonable maintenance, your 5.7L
Hemi will be good for 150-200K (miles,