Mercury 1997 Cougar Manual page 218

3.8L engine only
Open the vent plug.
Remove coolant recovery reservoir cap.
Remove radiator pressure cap.
With the engine off and cool, add a 50/50
mixture of recommended cooling system fluid
and water to the radiator until full, then add
to the reservoir until the reservoir is at the
FULL-HOT level.
Close the vent plug.
Reinstall the coolant recovery reservoir cap
by installing the cap to the fully installed
position.
Reinstall the pressure cap to the pressure
relief position by installing the cap to the
fully installed position, and then backing off
to the first stop.
Start and idle engine until the radiator upper
hose is warm (this indicates the thermostat is
open and coolant is flowing through the
entire system).
Immediately shut off engine. Cover cap
completely with a thick cloth and cautiously
remove radiator pressure cap and add a
50/50 mixture of recommended coolant and
water until system is full.
Reinstall the radiator cap securely.
Remove the cap from the engine coolant
recovery reservoir and add a 50/50 mixture
of recommended cooling system fluid and
water to the FULL-HOT mark on the engine
coolant recovery reservoir. Check that
reservoir hose is not kinked.
Reinstall the reservoir cap.
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