G13 lifetime? Coolant change interval- is there one?

[mk2]

Just was wondering if there's a life limit to new coolant? Used to need changing every two years on G11.  Or is it sealed for the life of the system- as in until you change the pump, thermostat or temp sensor?

[cpcpeter]

While antifreeze properties of the coolant may last a while (and can be easily checked with a refractometer) the anti-corrosion properties do reduce over time.

Easy way of checking this is with a warm but not hot engine, carefully open up the expansion tank, dip in the positive of a multimeter set to volts and the other to a good engine ground.  Readings over 600mV mean the anticorrosion properties are starting to deteriorate and worth renewing.  Up to around 400mV is acceptable.

[mk2]

That's handy. How does it work? Is there a voltage 'injector' probe in the coolant system? As in, where does the voltage reading come from? Is it like a sacrificial anode setup, where a voltage is generated between the anode and the block, and the meter probe picks up the voltage difference between them, but only if the coolant "still works" as a corrosion suppressant? Lots of questions!

 

[cpcpeter]

The coolant must somehow act as an electrolyte and interacts with the metals in the engine. If the engine begins to corrode I’m guessing the electrolyte will begin to contain more ions which will increase the potential difference, so the lower the number the better! I don’t know exactly how it works but it’s a tip often referred to in Car Mechanics magazine.