In this day and age, with 5+ different coolant formulations out there you have to RTFM to find out the proper interval. On some cars it is easy, on other cars it is difficult. If you have a vertical or near vertical radiator with a radiator cap on top, then chances are it will be pretty straightforward...all you need to do is drain the block and radiator, refill with water, drain again, refill with water, drain again, then refill with coolant and distilled water (or whatever TFM specifies). I always do the final refill as follows: Fill system as full as possible, leaving radiator cap off Pinch upper and lower radiator hoses to "burp" system, adding more coolant as air pockets come out Start engine Turn on heater Wait for engine to come up to temperature, the thermostat to open, and all the air pockets to be forced out of the block Add more coolant until full Put radiator cap back on Allow engine to cool Check coolant level