A process for the preparation of polyethylene by polymerizing in a slurry ethylene and optionally one or more C3 to C10 alpha-olefins in a reactor system comprising a polymerization reactor and one or more first heat exchangers located outside the polymerization reactor where the slurry in the polymerization reactor is cooled by withdrawing slurry from the polymerization reactor, cooling the slurry in the one or more first heat exchangers and returning the cooled slurry to the polymerization reactor, wherein the one or more first heat exchangers are cooled by a first coolant having a temperature of 29° C. or higher.