ACTION NAPA AUTO Parts - 26

Ford 6.4L Powerstroke

Richard McCuistian

he Ford 6.4L Powerstroke engine has one of the most
complex cooling systems on the road. Servicing this
system is not for the novice; the service manual's
ﬂush-and-ﬁll procedure is 78 steps. The job is a lot
easier with an air lift tool.
This cooling system works extra hard because it absorbs heat from the exhaust system. There are two EGR
coolers, and the number 2 (vertical) cooler has a tap that
supplies coolant to the EGR valve. Coolant exiting the
EGR valve returns to the degas bottle, while coolant exiting the EGR coolers returns to the engine's cast aluminum
front cover. Just for comparison, the water pump moves
125 gal/min at 3000 engine rpm, which is a 25% higher
f low rate than the water pump in a 400-horsepower LS-1
Corvette engine at redline.

Coolant ﬂow to the EGR valve is throttled.
26

ACTION/NAPA * Spring 2015

There are two thermostats in the front engine cover,
but they share a single outlet. They clip into the thermostat housing, and a YouTube video shows an aftermarket
tool for installing them that includes a go-no-go gauge
for the longer thermostat. The short thermostat functions
normally to control coolant f low through the radiator,
while the longer one bypasses the radiator circuit and allows coolant to return to the water pump. The longer thermostat has been the subject of a recall: failure (hyperextension) causes radiator leaks, and an updated thermostat
has been released to fix this problem. Both radiator hoses
have also been updated with double O-rings to prevent
minor seepage that causes a release of cooling system
pressure and subsequent cavitation. There is also a recall
(TSB 11-12-4) requiring replacement of the dual-port degas bottle with a single-port bottle (some folks just block
the upper port).
Cavitation is an issue in these engines, and using the
correct coolant is just as important as using the correct
oil. A notice in the service manual warns: "Not all coolants contain a nitrite additive package. Failure to have
nitrite in the cooling system may result in major corrosive
damage to the engine cooling system components." There
is a special Motorcraft additive with the right coolant
chemistry for this engine.
If coolant temperature at start-up is less than 136˚F
(58˚C), the Powertrain Control Module (PCM) will estimate how long it should take for the coolant to reach thermostat opening temperature. If the coolant does not reach
the predicted temperature, the PCM will set trouble code
P0128 or P007B and the malfunction indicator lamp will
be illuminated. Other cooling system codes are P0217 (engine over temp), P1285 (cylinder head over temp), P1299
(cylinder head over-temp protection active), P0125 (insufficient coolant temp for closed loop fuel control), and
P0480, P0481 and P0482 that indicate cooling fan malfunctions. "Over temp protection" means the PCM has
reduced the engine's power output to control temperature.
When looking up service information for this engine,
make sure to check for the latest TSBs too. Many have
been superseded over the years, particularly those for the
cooling system. ❆

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