A car is great to own right up until the heavy maintenance schedule lands on your desk. Day-to-day running costs are easy enough to absorb, but once an odometer crosses 90,000 miles, the big-ticket parts come due. Mechanic shops tend to see slower bay traffic in mid-week slots and late winter, which is usually when you have the most leverage to ask for a better labor rate.
When you replace a timing belt, the water pump sits directly behind it, so paying for both at once keeps you from paying duplicate labor down the road. Always negotiate the repair total with the shop first before you talk about payment. Spreading that $850 bill over time protects your emergency fund, but only if you have a clear plan to avoid carrying high interest.
That 0% intro rate is a firm deadline, not free money. If you have any part of the $850 balance sitting on the account when the 15 months end, the remaining balance will start collecting interest at the regular variable APR, wiping out the benefit of pacing the cost.