Coolant Antifreeze – Engine Cooling And Testing Made Easy

Coolant Antifreeze - Engine Cooling And Testing Made Easy
Coolant Antifreeze - Engine Cooling And Testing Made Easy

The job of Coolant Antifreeze is to protect the engine from severe temperature and corrosion.

Always flush and replace your coolant antifreeze at recommended intervals, or it will break down and not perform its job.

If coolant antifreeze quality prematurely degrades, severe damage to the engine and coolant system can result.

Coolant Antifreeze – What Does It Do

Checking the strength of the coolant-antifreeze is just as important for hot weather driving as it is for cold weather.

A 50/50 mixture of ethylene glycol (EG) antifreeze and water will provide:

  • Boiling protection up to about 255 degrees F with a 15 psi cap.
  • Along with freezing protection down to -34 degrees F.

By comparison, a 50/50 mixture of propylene glycol (PG) antifreeze and water will provide:

  • Boiling protection to 257 degrees F.
  • Along with a freezing protection to -26 degrees F.

Increasing the concentration of antifreeze in the coolant will raise its boiling temperature and lower its freezing point.

Corrosion Caused By Electrolysis

Coolant also plays an important role in preventing corrosion caused by electrolysis.

Corrosion Caused By Electrolysis
Corrosion Caused By Electrolysis

Electrolysis occurs when two dissimilar metals start swapping electrons, causing the metals to corrode.

Today’s engines have:

  • Aluminum
  • Copper
  • Cast iron
  • Steel
  • Magnesium alloys

Electrolysis will slowly eat away at all the internal parts.

In fact, old coolant becomes a pretty good electrical conductor, accelerating internal electrolysis. The good news is that it’s pretty easy to check the conductivity of your coolant with a digital multimeter. As a result, If the conductivity is high, it’s time for a coolant flush and fill.

Coolant Antifreeze – Why Flush And Replace It

Flushing the cooling system helps remove old scale and rust. Consequently, The corrosion inhibitors in new antifreeze help prevent scale and rust buildup in the cooling system. New antifreeze helps keep the engine operating at its most efficient temperature regardless of operating conditions and outside temperatures.

When you don’t flush-replace the antifreeze at recommended intervals, chemicals start to break down and cannot perform their job. Rust and scale buildup can lead to radiator hose, water pump or thermostat failure.

Coolant Antifreeze – Testing For Electrolysis ( Using A Digital Multimeter ):

  • Corrosion can and will prematurely aid in cooling system failures. It usually starts with the water pump, radiator, heater core, and finally the thermostat.
  • To use your digital multimeter, start with a cool engine and open the radiator cap.
  • Never open the radiator cap when the engine is hot to help prevent burn injuries.
  • With the cap off, start the engine and let it idle unit it reaches operating temperature.
  • Take your multimeter, set it to DC voltage and place the negative probe on the negative battery terminal.
  • As for the positive probe, go ahead and dip that right into the coolant.
  • If the meter reads .4 volts or less, the coolant is good.
  • If it reads more than .4 volts, then the additives in the coolant that prevent electrolysis have broken down.

Testing Fan Motor Only

Unplug the wiring connector on the fan. Use a jumper wire from the battery to route power directly to the fan. If the fan motor is good, the fan should spin at normal speed when supplied with 12 volts. Noisy bearings or a slower than normal speed would indicate a worn motor.

Testing Coolant Temperature Sensor (ECT)

Testing Coolant Temperature Sensor (ECT)
Testing Coolant Temperature Sensor (ECT)
  • First be sure it is getting voltage at the harness. A bad harness, or cut in the wire, can cause the same symptoms as a bad (ECT).
  • To test the harness for voltage turn the key to the ON position. Use a multimeter to measure for 5 Volts DC.
  • The voltage may vary slightly but should be close to 5 Volts.
  • If you get a good reading than the harness is good. Move on to testing the engine coolant sensor itself.
  • If you do not get a good 5 volt reading than the harness is bad.
  • A sensor can be tested while still in the vehicle. You will need to be able to reach it with the multimeter probes.
  • The first test should be done with the engine cold.
  • To test it with a meter set it to Ohms to get a resistance reading.
  • Use the multimeter leads to touch the two prongs on the ECT were the harness plugs in.
  • A good reading with a cold engine should be between 1.5 and 2 Ohms. If no reading is seen than the sensor is bad.
  • Sometimes a sensor can still give a reading but not be working correctly. To test this do the same reading but with the engine warmed up.
  • When the engine is warm the resistance should drop. If it does not drop than the sensor is bad and needs replaced.


Follow the guidelines in your vehicle owner’s manual for flushing and replacing coolant-antifreeze. Also make sure you are using the proper type of coolant antifreeze recommended for your particular vehicle.

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