If you Owners Manual doesn't specify a recommend interval to replace the belt to avoid catastrophic failure, ask the service manager at your dealership. Some makers recommend replacing the belt at 60,000 miles, some 80,000 etc. Or you can buy a car with a timing chain instead of a belt (such as a Ford) that doesn't need replacement.
The timing belt itself is not a very expensive part . . . . it's the labor charge of disassembling the front of the engine to get in there.......therefore, most replace the belt while the engine is apart to replace a bad water pump.....and vice versa.
Should be changed at mileage recommended by car manufacture (see owners manual). Otherwise if belt looks frayed, cracked or loose.
It is important because engine will stop when it breaks. Stranding you and depending on engine possible expensive internal engine damage.
You go by the mileage. It's very important because if it breaks it could ruin the engine.
If you wait till the signs appear they will be sudden breakdown and lots of engine damage.
