2008 MERCEDES-BENZ GL550 coolant

241 Controls in detail
3-zone automatic climate control*
Residual heat and ventilation
With the engine switched off, it is possible
to continue to heat or ventilate the interior
for up to 30 minutes. This feature makes
use of the residual heat produced by the
engine.Activating
Switch off the ignition (page 41).
Press button9 (page 230).
The indicator lamp on the button
comes on.
Deactivating
Press button9.
The indicator lamp on the button goes
out.
Rear automatic climate control
The control panel is located at the rear of
the front center console.
iHow long the system will provide heating
depends on

the coolant temperature

the battery voltage
Regardless of the temperature and air volume
set on the automatic climate control panel, an
interior temperature is aimed at by 72°F (22°C)
and the blower runs on low speed to protect the
vehicle battery.
iThe residual heat is automatically turned off:

when the ignition is switched on

after about 30 minutes

if the coolant temperature is too low

if the battery voltage drops
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368 Operation
Driving instructions

Always secure items in the trailer to
prevent load shifts while driving.

When towing a trailer, check occasion-
ally to make sure the load is secure,
and that lighting and trailer brakes (if
so equipped) are functioning properly.

Take into consideration that when tow-
ing a trailer, the handling characteris-
tics are different and less stable from
those when operating the vehicle with-
out a trailer.
It is important to avoid sudden maneu-
vers.

The vehicle and trailer combination is
heavier, and therefore is limited in ac-
celeration and climbing ability, and re-
quires longer stopping distances.
It is more prone to reacting to cross
wind gusts, and requires more sensi-
tive steering input.

If possible, do not brake abruptly, but
rather engage the brake slightly at first
to permit the trailer to activate its
brake. Then increase the braking force.

If the transmission repeatedly shifts
between gears on inclines, manually
shift to a lower gear (select 4, 3, 2 or 1)
(
page 197).
A lower gear and reduction of speed re-
duces the chance of engine overload-
ing and/or overheating.

On very steep inclines, not manageable
with automatic transmission in1,
switch on off-road driving program
(
page 278) or LOW RANGE mode*
(
page 201).

When going down a long hill, shift into
a lower gear and use the engine’s brak-
ing effect.
Avoid riding the brakes, thus overheat-
ing the vehicle and trailer brakes.

If the engine coolant rises to an ex-
tremely high temperature (coolant tem-
perature needle approaching the red
zone) when the air conditioning is on,
turn off the air conditioning system.
Engine coolant heat can be additionally
vented by opening the windows,
switching the climate control fan speed
to high and setting the temperature
control to the maximum hot position.

Extreme care must be exercised since
your vehicle with a trailer will require
additional passing distance ahead than
when driving without a trailer.
Because your vehicle and trailer is
longer than your vehicle alone, you will
also need to go much farther ahead of
the passed vehicle before you can re-
turn to your lane.
!If the trailer should begin to sway, reduce
the vehicle’s speed immediately.
In no case attempt to straighten out the tow
vehicle and trailer by increasing the speed.
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372 Operation
Driving instructions
Emission control
Certain engine systems serve to keep the
toxic components of the exhaust gases
within permissible limits required by law.
These systems, of course, will function
properly only when maintained strictly ac-
cording to factory specifications. Any ad-
justments on the engine should, therefore,
be carried out only by qualified
Mercedes-Benz Light Truck Center autho-
rized technicians.Engine adjustments should not be altered
in any way. Moreover, the specified service
jobs must be carried out regularly accord-
ing to Mercedes-Benz servicing require-
ments. For details refer to the
Maintenance Booklet.
Coolant temperature
During severe operating conditions,
e.g. stop-and-go traffic, the coolant tem-
perature may rise close to approximately
248°F (120°C).
The engine should not be operated with
the coolant temperature above 248°F
(120°C). Doing so may cause serious en-
gine damage which is not covered by the
Mercedes-Benz Limited Warranty.
Warning!G
As with any vehicle, do not idle, park or op-
erate this vehicle in areas where combusti-
ble materials such as grass, hay or leaves
can come into contact with the hot exhaust
system, as these materials could be ignited
and cause a vehicle fire.
Warning!G
Inhalation of exhaust gas is hazardous to
your health. All exhaust gas contains carbon
monoxide (CO), and inhaling it can cause un-
consciousness 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 win-
dow fully open at all times.
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376 Operation
At the gas station
Low outside temperatures
(diesel engine)
To prevent malfunctions, diesel fuel with
improved cold flow characteristics is of-
fered in the winter months. Check with
your fuel retailer.Check regularly and before a long trip
Open the hood (page 378).
Example illustration GL 450 (GL 320 CDI,
GL 550 similar)
1Brake fluid
2Coolant level
3Windshield washer system and
headlamp cleaning system*
Engine oil level
For more information on engine oil, see
“Engine oil” (
page 380).
iDiesel engine:
If you have driven the vehicle until the tank is
empty, the fuel system needs to be bled
(
page 527).
!Diesel engine:
The engine is more susceptible to wear and
damage if you use

marine diesel fuel

heating oil

additives
The exhaust aftertreatment device will be
seriously damaged if you use

LOW SULFUR HIGHWAY DIESEL FUEL
(500 ppm SULFUR MAXIMUM)

any other diesel fuel with a sulfur content of
above 15 ppm
The use of such non-approved fuels and/or
special additives is not covered by the
Mercedes-Benz Limited Warranty.
!Do not fill the tank with gasoline. Do not
blend diesel fuel with gasoline or kerosine. The
fuel system and engine will otherwise be dam-
aged, which is not covered by the
Mercedes-Benz Limited Warranty.

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377 Operation
At the gas station
Brake fluid
Coolant
For normal replenishing, use water (pota-
ble water quality).
For more information, see “Coolant level”
(
page 381) and see “Fuels, coolants, lu-
bricants” (
page 562).Windshield/rear window washer
system and headlamp cleaning
system*
For more information on refilling the wash-
er reservoir, see “Windshield/rear window
washer system and headlamp cleaning
system*” (
page 383).
Vehicle lighting
Check function and cleanliness. For infor-
mation on replacing light bulbs, see “Re-
placing bulbs” (
page 504).
For more information, see “Exterior lamp
switch” (
page 143).
Tire inflation pressure
For more information, see “Checking tire
inflation pressure” (
page 395).
!If you find that the brake fluid in the brake
fluid reservoir has fallen to the minimum mark or
below, have the brake system checked for brake
pad thickness and leaks immediately. Notify an
authorized Mercedes-Benz Light Truck Center
immediately. Do not add brake fluid as this will
not solve the problem. For more information, see
“Brake fluid” (
page 564).
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378 Operation
Engine compartment
Hood
Opening
Warning!G
Do not pull the release lever while the vehi-
cle 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.
Warning!G
If you see flames or smoke coming from the
engine compartment, or if the coolant tem-
perature display indicates that the engine is
overheated, do not open the hood. Move
away from vehicle and do not open the hood
until the engine has cooled. If necessary,
call the fire department.
Warning!G
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 off com-
pletely before touching any components on
the vehicle. Comply with all relevant safety
precautions.
Warning!G
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.
Warning!G
Vehicles with gasoline engine:
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, diagnos-
tic socket) of the ignition system

with the engine running

while starting the engine

if ignition is “on” and the engine is
turned manually
Warning!G
Vehicles with diesel engine:
The engine is equipped with a high-voltage
electronic control unit for the injection
system. Because of the high voltage it is
dangerous to touch any components of the
injection system (injectors, electrical wires)
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381 Operation
Engine compartment
Adding engine oil
Example illustration GL 450 (GL 320 CDI,
GL 550 similar)
1Filler cap
Unscrew filler cap1 from filler neck.
Add engine oil as required. Never over-
fill with oil.
Be careful not to spill any oil when adding.
Avoid environmental damage caused by oil
entering the ground or water.
Screw filler cap1 back on filler neck.
For more information on engine oil, see
“Technical data” section (
page 562) and
(
page 564).
Transmission fluid level
The transmission fluid level does not need
to be checked. If you notice transmission
fluid loss or gear shifting malfunctions,
have an authorized Mercedes-Benz Light
Truck Center check the automatic trans-
mission.
Coolant level
The engine coolant is a mixture of water
and anticorrosion/antifreeze.
When checking the coolant level

the vehicle must be parked on level
ground

the coolant temperature must be below
158°F (70°C)
!Only use approved engine oils and oil filters
required for vehicles with Maintenance System.
For a listing of approved engine oils and oil
filters, refer to the Factory Approved Service
Products pamphlet (USA only) in your vehicle
literature portfolio, or contact an authorized
Mercedes-Benz Light Truck Center.
Using engine oils and oil filters of specification
other than those expressly required for the
Maintenance System, or changing of oil and oil
filter at change intervals longer than those called
for by the Maintenance System will result in
engine or emission control system damage not
covered by the Mercedes-Benz Limited
Warranty.
!Excess oil must be siphoned or drained off.
It could cause damage to the engine and/or
catalytic converter (gasoline engine) or the oxi-
dation catalyst (diesel engine) not covered by
the Mercedes-Benz Limited Warranty.
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382 Operation
Engine compartment
The coolant expansion tank is located on
the driver’s side of the engine compart-
ment.
1Cap
2Coolant expansion tank
3Indicator wall
4Coolant levelUsing a rag, turn cap1 slowly approx-
imately one half turn counterclockwise
to release any excess pressure.
Continue turning cap1 counterclock-
wise and remove it.
Coolant level4 is correct if the level:

for cold coolant: reaches the top of
indicator wall3 visible through the
filling opening

for warm coolant: is approximately
0.6 in (1.5 cm) higher
Add coolant as required.
Replace and tighten cap1.
For more information on coolant, see
“Coolants” (
page 567).
Warning!G
In order to avoid potentially serious burns:

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.

Do not remove pressure cap on coolant
reservoir if coolant temperature is
above 158°F (70°C). Allow engine to
cool down before removing cap. The
coolant reservoir contains hot fluid and
is under pressure.

Using a rag, slowly open the cap approx-
imately 1/2 turn to relieve excess pres-
sure. If opened immediately, scalding
hot fluid and steam will be blown out
under pressure.

Do not spill antifreeze on hot engine
parts. Antifreeze contains ethylene
glycol which may burn if it comes into
contact with hot engine parts.
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