Volvo S80 Owner's Manual page 151

Follow the instructions on the packaging when topping up coolant.
It is important that the mixture of coolant concentrate and water is correct
for the prevailing weather conditions.Never top up with water only.
The risk of freezing increases with both too little and too much coolant
concentrate.
See capacities and recommended grade for fluids and oils on page 160.
Always use coolant with anti-corrosion agent as recommended by
Volvo.
New cars are filled with coolant that can withstand temperatures
down to approximately -35 °C.
Check the coolant regularly
The level should lie between the MIN and MAX marks on the
expansion tank.
Top up with fluid when the level has fallen to the MIN mark.
The engine must only be run with a well-filled cooling system.
High temperatures can occur, causing a risk of damage (cracks) to the
cylinder head.
The coolant may be very hot. If the coolant requires topping up
when the engine is at operating temperature, unscrew the expansion
tank cap slowly to gently release the overpressure.
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