Unfortunately, there’s no universal answer to this question. Each vehicle is different, and there aren’t any tried and true signs to look for in determining if a radiator flush is necessary.
However, your owner’s manual should suggest how often your vehicle needs a radiator flush, and it’s important to stay on top of this maintenance. Also, consider getting a second opinion from an ASE-certified mechanic.
It’s also worth noting that flushing the radiator yourself may be more trouble than it’s worth. Radiator pressure and fluids can be dangerous, and your car could be damaged should something go wrong.
Watch this YouTube video on how to properly flush your vehicle’s radiator coolant:
