Weber is president of Virginia-based Write Stuff. He is an award-winning freelance automotive and technical writer and photographer with over two decades of journalism experience. He is an ASE-certified Master Automobile Technician, and has worked on automobiles, trucks and small engines. He is a member of the Society of Automotive Engineers (SAE) and numerous other automotive trade associations. He has worked as an auto mechanic, a shop manager and a regional manager for an automotive service franchise operation.
Confusion continues over coolant colors for cars. Of course, there is still the good old green stuff, but there is also orange, yellow (gold and amber), red, pink, blue and, if you mix the wrong things together, brown.
Despite the rainbow of colors, all antifreeze starts out colorless. Dyes are added to differentiate one brand from another, one formulation from another, and to help us see how much coolant is in that reservoir under the hood. Unfortunately, there is no universal, standardized coolant color code.
In this article, we will use the term antifreeze when referring to undiluted bottles or bulk product. We will use the term coolant once it is mixed with water — preferably distilled water.
Most antifreeze is more than 90% ethylene glycol. (Non-poisonous — actually, “less” poisonous — antifreeze is propylene glycol.) To this base, antifreeze makers add a variety of chemicals that prevent rust and corrosion as well as a solvent to keep those inhibitors in solution and usually a bit of water. It’s the rust and corrosion inhibitors that cause all the color confusion.
The old-fashioned green stuff that we have used in America for generations contains phosphates and silicates for protection. American engines have long had iron blocks with aluminum cylinder heads and water pumps.
Phosphates are good at protecting iron from rusting and silicates are good at protecting aluminum. Silicates work fast and rush to protect aluminum surfaces whenever they are damaged. This is particularly important for water pumps. Left unprotected, bubbles in the coolant cling to the pump’s internal housing surfaces and when the bubbles burst, pock marks develop. The term for this is cavitation. Silicates scurry in to protect newly exposed aluminum from further damage.
When the aluminum erodes, the pump efficiency drops and the pump eventually fails.
Meanwhile, metal particles circulate throughout the rest of the cooling system. High temperatures and high engine speeds lead to more rapid water pump wear than engines that are driven gently.
Phosphates also protect aluminum, but not as rapidly as silicates. Phosphates also do a good job of protecting ferrous metals (iron and steel) from rust. Air in the system is a major contributor to rust — even a little bit of air.