The timing belt is a thick rubber belt located in the engine compartment behind the drive belts contained under the timing cover. Its job is to keep the crankshaft in sync with the camshaft(s), ensuring the proper timing and operation of the engine valves and therein, the engine. It is recommended to follow the maintenance schedule provided by the manufacturer of your vehicle and replace the timing belt as recommended. The timing belt drives the water pump in 60% of the cars. The labor cost of replacing the water pump is significantly higher than the cost of the pump in those cases. In cases where the water pump is behind the timing cover, when you are replace the timing belt, it is also cost effective to replace the water pump. We highly recommend replacing the timing belt pulleys, tensioners and oil seals located behind the timing cover as well. The tensioner applies pressure to the timing belt keeping it tight, while the pulleys keep the timing belt in line. These components are sealed units that contain bearings (they cannot be lubricated on a regular basis). The bearings wear out over time and may seize. If that happens, it may cause the timing belt to come off, which can cause major internal engine damage. Ignoring the replacement of a timing belt as a part of scheduled maintenance, could result costly repairs and major engine failure down the road. You should not wait for your timing belt to break, it must be serviced regularly, when your manufacture recommends it.