2012 MERCEDES-BENZ G-Class engine overheat

Turn off the engine before refueling.
Whenever you are around gasoline, avoid
inhaling fumes and any skin or clothing
contact.
Direct skin contact with fuels and the
inhalation
of
fuel vapors are damaging to your
health. G
WARNING
Overfilling of the fuel tank may create
pressure in the system which could cause a
gas discharge. This could cause the gasoline
to spray back out when removing the fuel
pump nozzle, which could cause personal
injury.
! Do not

use diesel to refuel vehicles with a
gasoline engine. Even small amounts of the
wrong fuel result in damage to the fuel
system and engine.
! Do not switch on the ignition if you
accidentally refuel with the wrong fuel.
Otherwise, the fuel will enter the fuel lines.
Notify a qualified specialist workshop and
have the fuel tank and fuel lines drained
completely. Gasoline
Fuel grade !
You should only refuel with unleaded
premium-grade gasoline as this avoids
damaging the catalytic converter.
If engine running problems are apparent,
have the cause checked immediately and
repaired. Excess unburned fuel can
otherwise enter the catalytic converter,
leading to overheating and possibly
causing a fire.
i Only refuel

with premium-grade unleaded
gasoline with a specified minimum octane
number of 91 (average value of 96 RON/
86 MON).
You will usually find information about the
fuel grade on the pump. If you cannot find the label on the gasoline pump, ask the gas
station staff.
You
can

find more information under "Fuel"
(Y page 273), by contacting an authorized
Mercedes-Benz Service Center or by
visiting http://bevo.mercedes-
benz.com.
! Use a filter when refueling from a fuel can.
Otherwise, the fuel lines and/or injection
system could be blocked by particles from
the fuel can. Refueling
Fuel filler flap When you open or close the vehicle with the
SmartKey, the fuel filler flap is automatically
unlocked or locked.
The position of the fuel filler cap
8
is
displayed in

the instrument cluster. The arrow
next to the filling pump indicates the side of
the vehicle. The fuel filler flap is located to the
rear on the right. Example: G 550 fuel filler cap
:
To open the fuel filler flap
; Tire pressure table
= Fuel type
? To insert the fuel filler cap
Opening X
Switch off the engine. Refueling
125
Driving and parking Z

accelerate. This could lead to accidents and
injury.
Rolling with the engine switched off G
WARNING
There is no power assistance for the steering
and the

brake when the engine is not running.
Steering and braking requires significantly
more effort and you could lose control of the
vehicle and cause an accident as a result.
Do not turn off the engine while the vehicle is
in motion.
Exhaust check G
WARNING
Inhalation
of exhaust gas is hazardous to your
health. All exhaust gas contains carbon
monoxide (CO), and inhaling it can cause
unconsciousness and possible death.
Do not

run the engine in confined areas (such
as a garage) which are not properly ventilated.
If you think that exhaust gas fumes are
entering the vehicle while driving, have the
cause determined and corrected
immediately. If you must drive under these
conditions, drive only with at least one
window fully open at all times.
Certain engine systems are designed to keep
the level of poisonous components in exhaust
fumes within legal limits.
These systems only work at peak efficiency
when they are maintained exactly in
accordance with the manufacturer's
specifications. For this reason, all work on the
engine must be carried out only by qualified
and authorized Mercedes-Benz technicians.
The engine settings must not be changed in
any circumstances. Furthermore, all specific
service work must be carried out at regular
intervals and in accordance with the
Mercedes-Benz service requirements. Details
can be found in the Maintenance Booklet. Brakes
Important safety notes G
WARNING
On
slippery road surfaces, never downshift in
order to obtain braking action. This could
result in

drive wheel slip and reduced vehicle
control. Your vehicle's ABS will not prevent
this type of control loss.
Do not engage the transfer case in position
LOW when driving on ice or packed snow. At
speeds below 18 mph (30 km/h) vehicle
steering is adversely affected by the Off-road
ABS.
Downhill gradients !
On long and steep gradients, you must
reduce the load on the brakes by shifting
early to

a lower gear. This allows you to take
advantage of the engine braking effect and
helps avoid overheating and excessive
wear of the brakes.
When you take advantage of the engine
braking effect, a drive wheel may not turn
for some time, e.g. on a slippery road
surface. This could cause damage to the
drive train. This type of damage is not
covered by the Mercedes-Benz warranty.
Heavy and light loads G
WARNING
Depressing
the brake pedal constantly results
in excessive

and premature wear to the brake
pads.
It may also cause the brakes to overheat,
seriously impairing their effectiveness. It may
then not be possible to stop the vehicle in
sufficient time to avoid an accident.
If the brakes have been subjected to a heavy
load, do not stop the vehicle immediately, but
drive on for a short while. This allows the
airflow to cool the brakes more quickly. 130
Driving tips
Driving and parking

i
Hill start assist will aid you when pulling
away on a hill.
For further information, see "Hill start
assist" ( Y page 117).
Maximum gradient-climbing capability On good road surface conditions, the
maximum
gradient-climbing
capability is 80%,
which corresponds to an approach/
departure angle of 38°. Note that the
vehicle's gradient-climbing capability
depends on the off-road conditions.
Accelerate carefully and make sure that the
wheels do not spin when driving on steep
terrain.
i If the load on the front axle is reduced
when pulling away on a steep uphill slope,
the front wheels have a tendency to spin.
4ETS detects this and brakes the wheels
accordingly. The rear wheel torque is
increased, making it easier to drive off.
Brow of hill When driving on an uphill gradient, reduce
pressure slightly on the accelerator
immediately
before

reaching the top of the hill
(do not shift the transmission to position N).
Use the vehicle's own impetus to drive over
the top of the hill.
This style of driving prevents:
R the vehicle from lifting off the ground on the
brow of a hill
R loss of traction
R the vehicle from traveling too quickly down
the other side
Driving downhill R
Before tackling steep downhill gradients,
select shift range 1 (Y page 121).
This way you use the engine's braking
effect to reduce the speed. If this is not
sufficient, brake gently. When doing so, make sure that the vehicle is facing in the
direction of the line of fall.
R Observe the notes on driving in
mountainous terrain (Y page 139).
R Drive slowly.
R Do not drive at an angle down steep
inclines. Steer

into the line of fall and drive
with the front wheels aligned straight.
Otherwise, the vehicle could slip sideways,
tip and roll over.
R Check that the brakes are working normally
after a long downhill stretch.
i The special off-road ABS(Y page 54)
enables accurate, brief and repeated
locking of the front wheels, causing them
to dig into the loose ground. Note that when
the front wheels are fully braked, they slide
easily over the surface of the ground,
making it difficult to steer. Driving systems
Cruise control
Important safety notes Cruise control maintains a constant road
speed for you. On long and steep downhill
gradients, especially if the vehicle is laden,
you must select shift range 1, 2 or 3 in good
time. By doing so, you will make use of the
braking effect of the engine, which relieves
the load on the brake system and prevents
the
brakes

from overheating and wearing too
quickly.
Use cruise control only if road and traffic
conditions make it appropriate to maintain a
steady speed for a prolonged period. You can
set any road speed above 20 mph
(30 km/h). G
WARNING
The cruise control is a convenience system
designed to assist the driver during vehicle
operation. The driver is and must always Driving systems
139
Driving and parking
Z

Useful information
i This Operator's Manual describes all
models and all standard and optional
equipment of your vehicle available at the
time of publication of the Operator's
Manual. Country-specific differences are
possible. Please
note that your vehicle may
not be equipped with all features
described. This also applies to safety-
related systems and functions.
i Please read the information on qualified
specialist workshops (Y page 20). Important safety notes
You will find an illustration of the instrument
cluster in the "At a glance" section
(
Y page 25).
G
WARNING
A driver's attention to the road and traffic
conditions must always be his/her primary
focus when driving.
For your safety and the safety of others,
selecting features through the multifunction
steering wheel should only be done by the
driver when

traffic and road conditions permit
it to be done safely.
Bear in mind that at a speed of just 30 mph
(approximately 50 km/h ), your vehicle is
covering a distance of 44 feet (approximately
14 m) every second. G
WARNING
No messages will be displayed if either the
instrument cluster or the multifunction
display is inoperative.
As a result, you will not be able to see
information about your driving conditions,
such as
R speed
R outside temperature
R warning/indicator lamps R
malfunction/warning messages
R failure of any systems
Driving characteristics may be impaired.
If you

must continue to drive, do so with added
caution. Contact an authorized Mercedes-
Benz Center as soon as possible. G
WARNING
Malfunction and warning messages are only
displayed for certain systems and are
intentionally not very detailed. The
malfunction and warning messages are
simply a reminder with respect to the
operation of certain systems. They do not
replace the owner's and/or driver's
responsibility to maintain the vehicle's
operating safety. Have all required
maintenance services and safety checks
performed on

the vehicle. Bring the vehicle to
an authorized Mercedes-Benz Center to
address the malfunction and warning
messages. Displays and operation
Tachometer
The red

band in the tachometer indicates the
engine's overrevving range.
! Do not drive in the overrevving range, as
this could damage the engine.
The fuel supply is interrupted to protect the
engine when the red band is reached. Displaying the coolant temperature
G
WARNING
Driving when your engine is overheated can
cause some

fluids which may have leaked into
the engine compartment to catch fire. You
could be seriously burned.
Steam from an overheated engine can cause
serious burns which can occur just by opening 152
Displays and operation
On-board computer and displays

Display messages Possible causes/consequences and
M Solutions?
Coolant
Stop,
Turn
Engine Off The coolant is too hot.
X
Pull over and stop the vehicle safely and switch off the engine,
paying attention to road and traffic conditions.
X Make sure that the air supply to the radiator is not blocked, e.g.
by snow, slush or ice.
X Wait until the display message disappears before restarting the
engine. Otherwise, there is a risk of engine damage.
X Pay attention to the coolant temperature display.
X If the temperature increases again, visit a qualified specialist
workshop immediately. The poly-V-belt may have torn.
X
Pull over and stop the vehicle safely and switch off the engine,
paying attention to road and traffic conditions.
X Open the hood.
X Check whether the poly-V-belt is torn.
If the poly-V-belt is torn:
! Do not

continue driving. The engine could otherwise overheat.
X Consult a qualified specialist workshop.
If the poly-V-belt is not damaged:
X Wait until the display message disappears before restarting the
engine. Otherwise, there is a risk of engine damage.
X Pay attention to the coolant temperature display.
X Visit a qualified specialist workshop. G
WARNING
Driving when your engine is overheated can cause some fluids which may have leaked into the
engine compartment to catch fire. You could be seriously burned.
Steam from

an overheated engine can cause serious burns which can occur just by opening the
engine hood. Stay away from the engine if you see or hear steam coming from it.
Stop the vehicle in a safe location away from other traffic. Turn off the engine, get out of the
vehicle and do not stand near the vehicle until the engine has cooled down.
! If the coolant temperature exceeds 248 ‡(120 †) do not continue driving. The engine will
otherwise be damaged. Display messages
171
On-board computer and displays Z

Display messages Possible causes/consequences and
M Solutions? The engine fan is defective.
X
At coolant temperatures under 248 ‡ (120 † ), drive to the next
qualified specialist workshop.
X Avoid subjecting the engine to heavy loads, e.g. driving in
mountainous terrain, and stop-and-go traffic. # The battery is not being charged.
Possible causes are:
R
a defective alternator
R a torn poly-V-belt
R a malfunction in the electronics
X Pull over and stop the vehicle safely and switch off the engine,
paying attention to road and traffic conditions.
X Open the hood.
X Check whether the poly-V-belt is torn.
If the poly-V-belt is torn:
! Do not

continue driving. The engine could otherwise overheat.
X Consult a qualified specialist workshop.
If the poly-V-belt is not damaged:
X Visit a qualified specialist workshop. The battery voltage is too low.
X
Switch off electrical consumers that are not required.
X Have the battery and alternator checked at a qualified specialist
workshop. The battery has been charged or the vehicle has been jump-
started.
X
Have the battery and alternator checked at a qualified specialist
workshop. 4
Check
oil

level at
next gas station. The engine oil level has dropped to a critical level.
X
Check the oil level (Y page 211).
X If necessary, add engine oil ( Y page 213).
X Have the engine checked for leaks if the engine oil needs to be
refilled more often than usual. You have added too much engine oil. There is a risk of damaging
the engine or catalytic converter.
X
Siphon off excess engine oil until it is at the specified level.
Observe the legal requirements.172
Display messages
On-board computer and displays

Useful information
i This Operator's Manual describes all
models and all standard and optional
equipment of your vehicle available at the
time of publication of the Operator's
Manual. Country-specific differences are
possible. Please
note that your vehicle may
not be equipped with all features
described. This also applies to safety-
related systems and functions.
i Please read the information on qualified
specialist workshops (Y page 20). Engine compartment
Hood
Opening the hood G
WARNING
Do
not pull the release lever while the vehicle
is in motion. Otherwise, the hood could be
forced open by passing air flow.
This could

cause the hood to come loose and
injure you and/or others. G
WARNING
Do not open the hood when the engine is
overheated. You could be seriously injured.
Observe the coolant temperature gauge to
determine whether the engine may be
overheated. If you see flames or smoke
coming from the engine compartment, move
away from the vehicle. Wait until the engine
has cooled. If necessary, call the fire
department. G
WARNING
You
could be injured when the hood is open –
even when the engine is turned off.
Parts of the engine can become very hot. To
prevent burns,

let the engine cool completely
before touching any components on the
vehicle. Comply with all relevant safety
precautions. G
WARNING
To help prevent personal injury, stay clear of
moving parts when the hood is open and the
engine is running.
The radiator fan may continue to run for
approximately 30 seconds or may even
restart after the engine has been turned off.
Stay clear of fan blades. G
WARNING
The engine is equipped with a transistorized
ignition system. Because of the high voltage,
it is dangerous to touch any components
(ignition coils, spark plug sockets, diagnostic
socket) of the ignition system:
R with the engine running
R while starting the engine
R when the ignition is switched on and the
engine is turned manually
X Make sure that the windshield wipers are
switched off. G
WARNING
The windshield wipers and wiper linkage
could be set in motion.
When the hood is open, you or others could
be injured by the wiper linkage.
Make sure that the windshield wipers are
switched off

and that the SmartKey has been
pulled out of the ignition lock before opening
the hood.
The release lever on the hood is in the footwell
on the left-hand side of the vehicle when
viewed in the direction of travel. 210
Engine compartment
Maintenance and care

X
Turn the SmartKey to position
2(Y page 115) in the ignition lock.
X Check the coolant temperature display in
the instrument cluster.
The coolant temperature must be below
158 ‡ (70 †). G
WARNING
In order to avoid any potentially serious burns:
R use extreme caution when opening the
hood if there are any signs of steam or
coolant leaking
from the cooling system, or
if the coolant temperature display indicates
that the coolant is overheated.
R do not remove the pressure cap on the
coolant reservoir if the coolant temperature
is above 158 ‡ (70 †). Allow the engine to
cool down before removing the cap. The
coolant reservoir contains hot fluid and is
under pressure.
R using a rag, slowly turn the cap
approximately 1
/ 2 turn to relieve excess
pressure. If opened immediately, scalding
hot fluid and steam will be blown out under
pressure.
R do not spill antifreeze on hot engine parts.
Antifreeze contains ethylene glycol which
may burn if it comes into contact with hot
engine parts. X
Slowly turn cap : half a turn
counterclockwise and allow excess
pressure to escape.
X Turn cap : further counterclockwise and
remove it.
If the coolant is at the level of marker bar
= in the filler neck when cold, there is
enough coolant in coolant expansion
tank ;.
If the coolant is approximately 0.6 in
(1.5 cm) above marker bar = in the filler
neck when warm, there is enough coolant
in coolant expansion tank ;.
X If necessary, add coolant that has been
tested and approved by Mercedes-Benz.
X Replace cap : and

turn it clockwise as far
as it will go.
For further information on coolant, see
(Y page 276).
Windshield washer system and
headlamp cleaning system The washer fluid reservoir is used for both the
windshield
washer

system and the headlamp
cleaning system. G
WARNING
Washer solvent/antifreeze is highly
flammable. Do not spill washer solvent/
antifreeze on

hot engine parts, because it may
ignite and burn. You could be seriously
burned.
! At temperatures below freezing: always
fill the washer fluid reservoir with a mix of
water and windshield washer concentrate
(e.g. MB WinterFit). There is otherwise a
risk of damaging the windshield washer
system/headlamp cleaning system.
! Only use washer fluid concentrate which
is suitable for plastic lenses. Unsuitable
washer fluid concentrate could damage the
plastic lenses of the headlamps. 214
Engine compartment
Maintenance and care