How to keep your cool about coolants
You should guard against contamination from engine oil or automatic transmission fluid
Newer engine coolant may be designed to provide freeze protection and water-pump lubrication for up to 10 years, but this doesn’t help guard your vehicle’s engine against contamination-related failures.
The most common coolant contaminants are engine oil and automatic transmission fluid.
Engine oil can be introduced into the coolant passages in various areas, but cylinder-head or head-gasket failures are the most common. When this happens, engine coolant will take on a milky brownish-white consistency.
The easiest way to see the condition of an engine’s coolant is with the use of a simple coolant-strength tester. They are fitted with a kitchen-baster rubber bulb at one end and a black hose to draw in coolant at the other, and sell for less than $10 on average.
They can be used to test the freeze and boil points of any glycol-based coolant.
The clear plastic test chamber provides a great view of any contamination. If your ride has this type of problem, it will likely also exhibit some engine overheating, coolant loss, or poor running condition. It isn’t something you want to ignore.
The other common intrusion concern comes from vehicles that have an automatic transmission cooler built into the bottom section of the radiator. With age, the core tubes in radiators can weaken and leak, resulting in cross contamination between engine coolant and transmission fluid. By the time drivers notice this type of failure, the transmission has often stopped working because of a lack of fluid.
If you ever have to top up coolant, never use tap water. The minerals in it can create scaling over time, and it doesn’t take much to clog narrow coolant passages. The first symptom most owners will notice is a lack of heat from the cabin’s climate control system, as the scaling constricts the passages in the heater core.
When faced with this job, many technicians use a descaling agent — CLR, for instance — when flushing out a cooling system plagued by scale buildup. When purchasing coolant for top-ups, always buy the premixed stuff that’s correct for your ride; this way, there’s no worry about getting the wrong freeze point. Pure, undiluted coolant actually will start icing up at higher temps than plain water. If your parts store staff isn’t sure of the correct type of coolant, don’t guess — mixing different coolant types together can weaken freeze protection and damage seals and gaskets. Your factory dealership should have the correct blend.
Finally, if we need to remind you never to remove a coolant pressure cap when the engine is hot or warm, perhaps you should just leave the hood closed.