Mercedes-Benz 2005 SLK-Class Operator's Manual page 428

Technical data
Fuels, coolants, lubricants, etc.
Anticorrosion/antifreeze quantity
Model
SLK 350
SLK 55 AMG
428
Approx. freeze protection
–35°F (–37°C)
5.4 US qt (5.1 l)
5.9 US qt (5.5 l)
–49°F (–45°C)
6.0 US qt (5.6 l)
6.4 US qt (6.1 l)