fan belt

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A taut rubber belt that transfers torque from the crankshaft to the shaft of the cooling fan on an engine.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A loop of material, typically reinforced rubber with a trapezoidal cross-section, by which a motor or engine turns a fan so that it can cool itself.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a belt driven by the crankshaft that drives a fan that pulls air through the radiator