Thurston Car Talk: Is A Coolant Flush Necessary


Submitted by Bron of Bron’s Automotive

I am sometimes asked if it’s really necessary to perform a coolant flush.  A good place to start in answering that is to talk about what coolant does.  In years past we called it anti-freeze, which gave the impression that this was its only job.  The primary job of coolant is to transfer excess heat from the engine to the radiator, where the heat can be removed to the surrounding air.  The best fluid for transferring heat is pure water, however at 190 degrees Fahrenheit, water is extremely corrosive to the inside of your engine.  For this reason it’s mixed 50/50 with anti-freeze, or coolant which contains anti-corrosion additives.  If coolant is not mixed with water, your engine can run hotter than normal as the pure coolant struggles to transfer heat.  Coolant also has anti-cavitation additives to prevent cavitation around the water pump impeller.

The interesting thing about these chemical additives is that they wear out over time, much the way prescription drugs lose their potency and effectiveness over time, hence the discard date on pill containers.  We want to flush coolant before the anti-corrosion additives lose their effectiveness.

Another consideration is that the current the engine starter uses returns to the battery negative terminal by running from the starter through the block to where the big black cable is attached, and then back to the battery negative terminal.  It may sound hard to believe, but this can build up a slight charge in the engine coolant over a long period of time, resulting in a condition called electrolysis.  Electrolysis will cause metal to come off the inside of your engine and be deposited in the radiator and heater core, which explains why we sometimes find that a failed radiator we take out is significantly heavier than the new one we install! (This is how the electroplating process works) The same holds true for heater cores, which can be very difficult to access and replace.

So the answer to the coolant flush question is a resounding YES.  We want to flush out the coolant and replace it with new before it is visibly bad, due to additive depletion and the possibility of electrolysis.  The usual time frame is two years or 30,000 miles for standard coolant, however some carmakers have extended  life coolant that can go longer.  The bottom line is that flushing and keeping the coolant fresh is always less expensive than repairing a heater core or radiator, or head gasket.

About The Author

Bron Lindgren has been an Olympia resident since 1975. He has been working on vehicles as a technician since the late 1970’s, and started his own shop, Bron’s Automotive in 2002. Bron hires only ASE certified technicians, is an AAA approved auto repair shop, and provides shuttle service as well as a 2 year/24,000 warranty. Bron is a member of the West Olympia Rotary, the Automotive Service Association, Thurston County Chamber, and a board member of the Community Mental Health Foundation, BHR’S fundraising arm.

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