Q: Mixing red and green coolant in the radiator

Realize that green antifreeze is the old style antifreeze. That was an old type of antifreeze where the glycol lasts maybe three years max. So you’ve got to change the coolant maybe three years or every 15,000 miles. The modern coolant comes in various different colors and red happens to be one of them. It often can last five years or 150,000 miles. So it’s a better antifreeze to use.

Now, if you mix them--they are not supposed to be mixed--but if you mix them it’s not like mixing an acid and a base and you are not going to have and explosion or anything like that. It’s just that, when you do mix them, then when you use any of the machines that mechanics use to see what the freeze point is, you’re going to get inaccurate readings. So if somebody tries to check to see if you have enough antifreeze in your system, so it won’t freeze in the winter for example, your reading might be wrong. If it gets really cold, you might end up cracking your engine. So basically, you’d want to stick to the coolant that the car was made for. If you have an older car, say that came with green coolant, you can flush it all out and put the newer style coolant in and then change it every five years or 150,000 miles. It’s perfectly backwards compatible if you want to do that. But you really don’t want to mix them, it’s not that good of an idea to mix them. If you want to have the correct coolant added for you, consider YourMechanic. They will be able to come to your home or office to perform this service.