lars

Rock Auto's June newsletter says that it's a good idea to replace coolant before it turns into a good enough electrolyte to start corroding metal parts of the coolant system, such as the heater core, water pump, etc. I've always believed this to be true and have been regularly replacing coolant in my cars for 40 years.

Rock Auto says that an easy way to see if coolant is encouraging electrolysis is to use a multimeter to check the voltage, with one probe in the coolant and the other connected to ground. Readings under 0.4 volts indicate the coolant is OK.

I have two cars at home right now. One is a classic on which the coolant was last changed in 2012, 4,000 miles ago. The voltage test for its antifreeze shows 0.11 volts. The other car is my CLK500, on which the dealer flushed and replaced the antifreeze five months ago. The voltage reading on its coolant is 12.4 volts.

What gives here? Are there no metal parts in the cooling system?

DanielFD

oh wow, never heard of anything like this. i just change coolant every year. Subscribed to see if anybody has a clue.

Rudeney

Sounds like you have an electrical short somewhere. The only places I can think of where coolant would come in contact with something electrical are the coolant level sensor int he expansion reservoir or the small electric "REST" pump (if equipped) right at the reservoir. Unplug those and see if the voltage persists.