Is there any difference between antifreeze and coolant, and if so, what is it? Are their chemistries different or not, and does it really matter?
Can I just use plain old water in my car? And what about the orange stuff vs. the green stuff? Why are there so many choices? Sometimes a person just wants a coffee (for instance), and it's not like more choices are helpful!
What Is the Difference Between Antifreeze and Coolant?
It's actually really simple: antifreeze is undiluted coolant. Antifreeze is just a full-strength solution of either propylene glycol or ethylene glycol and other ingredients.
Propylene glycol is actually less toxic than ethylene glycol, but regardless of the main ingredient in your antifreeze, coolant is what either solution is called when diluted 50-50 with distilled water.
You want to make sure to only ever pour coolant into your car's cooling system. It's a bit counterintuitive, but antifreeze doesn't offer the same protection as coolant does, whether you're talking protection from freezing or from boilovers. That's just how the chemistry works - it's actually better when it's mixed with water.
It used to be that you had to buy jugs of antifreeze and dilute them to make coolant yourself, but these days life is so dadgum convenient that you can buy coolant premixed right off the shelf. Now that is handy indeed, but what if you have a car that requires the newer orange stuff, not the usual green stuff?
Orange vs. Green
This distinction, too, is really simple. The difference in color just comes down to which chemical rust inhibitor is mixed in with the fluid. Newer cars that require the orange formula typically have more aluminum components in their cooling systems, so they require a different chemical mix than older-style cars do.
It's important that you don't mix orange with green, as those rust inhibitors won't play nicely together. There are indeed some green varieties that state on the label they are suitable for any system, but be careful to read up on all manufacturer suggestions concerning your vehicle before proceeding.
It is possible to just use water in your vehicle's cooling system, but it's not advisable in most situations. Some race applications prohibit the use of coolant in an effort to preserve the track surface in the event of total system failure.
For instance, it's better if a car pukes water onto a dragstrip instead of gallons of very slick ethylene glycol. In these cases, most racers use distilled water in an effort to keep mineral content in the system to a minimum.
You may indeed live in Death Valley and never need freeze protection, but coolant also performs another crucial task: lubricating your water pump. So unless you want to have it seized up from neglect any time soon, you better just go ahead and plan on using coolant.
Now that this is all as clear as mud, just remember to match the colors, whether green or orange, to what's in your car right now. And it's best to buy the stuff that says right on the bottle that it's pre-mixed 50-50 coolant.
Keeping those two things straight will keep your car from breaking a sweat and ensure that your water pump stays lubricated. Avoid using plain water. Buy the correct color for your car, and don't worry too much about the chemical intricacies of your cooling system.