Is it recommended to wait until it reaches the recommended mileage before changing the timing belt even if it is already 3 or more years

  • Better to know the specifics of your vehicle before making a suggestion. Certain vehicles (eg Volvo) I would advise my customers to replace before the mileage "expires". Also, most maintenance schedules recommend a CHECK of the timing belt at regular intervals (perhaps every 25k - 40k miles) to potentially discover a fraying, cracking, teeth chipped, or worn belt before any issues arise. Some vehicles (notably Subaru) use the back "smooth" portion of the timing belt to drive the water pump. This makes both surfaces critical in these applications. Beyond this, there is only opinion.
    – SteveRacer
    Oct 13 '17 at 2:34

The condition of a rubber timing belt will deteriorate both through wear during use and through exposure to the elements (temperature cycles, salt, rain etc) which is why both the mileage and the age matter.

It's difficult to be more specific without knowing the exact make and model of the car, as SteveRacer points out some cars such as Subaru's have a belt configuration that means they are more sensitive to belt aging than others but I can't think of one where I wouldn't recommend changing the belt on whichever condition occurs first age or mileage. A timing belt failure can easily scrap most engines so while it's often an expensive job it's far cheaper than an engine rebuild/replacement so ignoring it is false economy.

  • And usually in most manuals it mentions the "use" of the vehicle - change more frequently for lots of stop / start driving or mostly motorway use etc.
    – Solar Mike
    Oct 13 '17 at 9:36
  • @SolarMike yep.. the "jolt" the belt receives when starting the engine or from sudden changes in rpm means that frequent, short journeys can be more wearing then infrequent longer ones, another reason for the timed aspect to the change schedule. Oct 13 '17 at 9:44

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