How to determine it's time to change your antifreeze.

Antifreeze is the lifeblood of your car's cooling system. Between two to five years is the usual service interval.  How old is the antifreeze in your Cad / LaSalle?  I know mine is probably 5 years old.    After that amount of time, the anti-corrosion additives have worn out / been used up.

Many of us have probably used the old "turkey baster" tester which I believe reports specific gravity of the fluid being tested.  These typically tell you how hot or cold the antifreeze can provide protection for.







However, this type of instrument won't tell you the 'quality' of the antifreeze or how much life it has left.

Here's the Tech Tip:   Did you know you can testing the anti-corrosion ability of the antifreeze by using a voltmeter?

A simple digital voltmeter can be bought for only a few dollars and has a multitude of uses. Worn out antifreeze can act like an electrolyte in a battery and uses up metal engine parts as part of its chemical reaction.  This will eat away at freeze plugs, aluminum water pumps, thermostat housings, etc.


To test the antifreeze, set the meter scale to 20 DC volts, then place the positive (+) lead into the antifreeze (not touching any part of the radiator, just the fluid), and the negative (-) lead on a good ground, like the engine.

Does the meter show a voltage reading?  A voltage reading of .2 volts is OK.  A reading around .5 volts should be considered marginal.  Anything above  .7 volts - your coolant needs to be flushed and replaced.

If you end up changing the antifreeze, consider also adding a water pump lubrication additive.  AC Delco makes "Radiator Anti-Rust & Water Pump Lubricant (11 oz.)" for example.  Part # X40





Now, while you've got the tester out, after measuring the voltage in the antifreeze above, let's check
your grounds.  Start the motor with no accessories on and measure the antifreeze again.  Same as above, positive in the antifreeze, negative to ground.   If you show MORE voltage than when the motor was off, then you have a system leaking electricity into the coolant.


If so, run the engine with all accessories on and watch the voltmeter as an assistant turns off the accessories one at a time, when the voltage drops below 0.01v (assuming good antifreeze) or it drops back to the voltage in the initial test with the motor off, you have found the circuit with a poor ground.  Do the same test while cranking the starter, a poorly grounded starter can destroy the radiator and or heater core in a matter of weeks.


One final tip to fight cooling system is to use a sacrificial anode (usually zinc).  Some are on the underside of the cap, some you hang in the fluid.  This metal gets eaten away before the other parts of you cooling system.  JC Whitney as them for $14.