Yes. You need a mixture of water and anti-freeze to operate properly. The water has the 212 boiling point, the antifreeze lets it go below 0 and also helps keep the water from damaging all the metal surfaces (rust). If overheating is an issue, you can run more than 50% water but run the risk in the winter of it freezing and cracking your engine. A better solution if your worrying about overheating is a bigger radiator and change your fluid every summer.