Mercedes-Benz OM 904-926 LA BlueTec Operating Instructions Manual page 76

Work schedules
74
X
Open the engine cooling system cap slowly,
relieving the excess pressure.
X
Check the antifreeze/corrosion inhibitor
concentration using a testing device. The
correct concentration of 50% antifreeze/
corrosion inhibitor by volume in the coolant
provides antifreeze protection down to
Ò37 †. If a lower level of antifreeze protec-
tion is indicated, correct the mixture ratio.
! If the concentration of antifreeze/corro-
sion inhibitor is too low, there is a risk of
engine damage as a result of corrosion/
cavitation in the cooling system.
Avoid concentrations greater than
55% by volume corrosion inhibitor/antifreeze
agent. Otherwise, the maximum antifreeze
protection down to Ò45 † will not be attained.
Heat dissipation and antifreeze protection
deteriorate at higher concentrations.
X
To check the coolant level: the cooling
system is filled correctly if the coolant is
level with the mark in the filler neck.
Cooling and heating system – condi-
tion check of radiator, lines and hoses
Special tool: pressure tester tool
X
Heating systems: open all control valves
and shutoff valves for the heating system.
X
Remove the coolant expansion tank cap.
X
Check the coolant level and top up if nec-
essary.
X
Check/correct the coolant antifreeze pro-
tection content.
X
Dry the inside of coolant filler neck ; with
a lint-free cloth.
X
Mount pressure tester tool : on the filler
neck of the coolant expansion tank.
X
Connect the compressed-air hose with tyre
inflation connection to pressure tester
tool : and set it to a test pressure of
1.0 bar.
The test pressure should correspond to the
value at which the cooling system pressure
relief valve opens. The opening pressure
can be determined from the code on the
cap or pressure relief valve.
Example: code 100 = 1.0 bar excess pres-
sure.
X
After about 5 - 10 minutes, read the drop
in pressure on the manometer of
tester :. After 5 - 10 minutes, there must
be no drop in pressure detected on the
manometer. Do not exceed the test pres-
sure and the test time, as this may damage
the cooling and heating system.
If the cooling system/heating system is
leaking, this will become apparent due to a
drop in pressure, indicated by the manom-
eter on tester :.
X
If there is a loss of pressure in the cooling
system leading to visible loss of coolant,
have the leak in the cooling or heating sys-
tem repaired.
X
If there is a pressure drop with no visible
loss of coolant: have the cause identified
and immediately rectified by a qualified
specialist workshop.
Mercedes-Benz recommends that you use
a Mercedes-Benz or MTU Service Centre
for this purpose ( Y
to safety or on safety-related systems must
be carried out at a qualified specialist work-
shop.
X
Release the pressure using pressure tester
tool : and remove pressure tester
tool : from the coolant expansion tank
filler neck.
page 11). Work relevant