by Alain Hoffmann
Left - Discovery , Right
The coolant reservoir is a large black plastic container with a screw-on
cap. The coolant should be an water-glycol mix of 50/50. Such a mix gives
a lower freezing and a higher boiling point as pure water or pure glycol.
This mix also works as rust inhibitor. Especially on the TDi's, V8s' and
TD5s' you may never run without this as it will corrode the engine inside
and hamper heat transfer.
You should NEVER leave coolant in an open container. It has a fatal
attraction on cats and dogs as it's so sweet. And if they drink it they
DIE!! And a terrible death it is. .
Coolant level should never be checked when engine is hot. Even when almost
cold you still have some pressure. So put your hand on the cap and turn
it slowly as shown in the picture above (the engine was cold when I did
this). If you have the slightest doubt wear heavy gloves or put a thick
rag on the cap. If your engine overheated put a piece of floor carpet
over the cap and try to turn it. Those carpets are almost a barrier for
steam. Wait for the point when the pressure slowly hisses out. After this
it's safe to unscrew the cap.
Coolant level with engine cold should be around the outer lip of the tank
as shown below. Don't overfill, excess liquid will be pushed out..
If need is you can always top up with normal water. If I have to do this
from time to time I make sure I use undiluted glycol next time for topping
up (above right).
In an emergency you can use almost any liquid as long as it's not salty.
Of course it must be evacuated and rinsed as soon as possible. The only
liquids not to use are saltwater, oil and brake fluids. If the engine
overheated and you haven't enough liquid you can either shut off and risk
a lockup or leave it at idle, remove the cap CAREFULLY and very slowly
pour in new liquid. Be prepared to get some vapour without warning. This
is only a recommendation, you do this at your own risk.
Those PLASTIC filler caps are mounted on top of the radiator(above). You
don't need to remove them in normal use. However after a great loss of
cooling fluid you must remove them and fill the system from here. Before
removing them you must remove the reservoir cap as shown above to release
the pressure. Fill up to about 1 cm below top level, then screw the cap
in CAREFULLY with a large screwdriver.
In case of an overheated engine you must slowly pour water in so the engine
doesn't get a shock.