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Engine Coolant

Coolant Leaks and Coolant Types

It is very important that antifreeze or engine coolant is changed every two years (four years for vehicles with long life coolant) to replenish the additives that protect the cooling system from rust, corrosion, pitting, electrolysis, gelling and foaming. Your automobile cooling system should have a concentration of 50% to 70% antifreeze to water at all times.

Vehicles using Extended Life antifreezes should be changed in about 50,000 miles or 4 years to prevent system damage and radiators and heater cores from plugging up.

Antifreeze Concentration Chart

Coroded water pump
The water pump on the left has been eaten away by bad coolant and electrolysis.

Is Antifreeze Really Important?

Yes, but not just because of the danger of freezing. Back in the early days of Automobiles when engines were very simple and made entirely of steel, water worked OK to cool the engine, after all it was drained regularly (sometimes nightly in the winter) to prevent rust and freezing. The first antifreeze solution consisted of alcohol, which prevented freezing but was inefficient and didn't prevent rust or corrosion. More stable and efficient solutions to prevent the coolant from freezing in the engine were soon created which were the forerunners of what we use today.

The modern antifreeze, however, does much more. It provides year-round protection of the cooling system: It prevents freeze up in winter and boil over in summer (especially in cars with air conditioning). It provides protection from rust and corrosion and does not harm rubber hoses and plastics.
A desirable antifreeze should not corrode metal parts, attack rubber, become viscous at low temperatures, or evaporate readily at the ordinary engine operating temperature. It should be chemically stable, a good conductor of heat, and a poor conductor of electricity (which causes electrolysis).

The performance requirements of automobile antifreeze became more severe during the 1980's. The reduction of the overall mass of vehicles to improve fuel economy entailed extensive use of light materials such as aluminum and plastics for the construction of engine and cooling system parts.

The volume of antifreeze used was also drastically reduced to further reduce weight, subjecting the antifreeze to high rates of flow, high temperatures and significant metal-to-coolant heat fluxes. Today's smaller, efficient and powerful engines dissipate more heat, requiring that the antifreeze keep the heat exchange surfaces in clean condition. In addition, corrosion, which in itself is of concern, can also result in heavy corrosion deposits that impedes heat transfer.

What is Electrolysis?

As the additives in your coolant that keep it neutralized become depleted over time, the coolant actually develops an electric charge from passing over dissimilar metals.
You can even measure this voltage with a voltmeter. This small electric current removes metal from engine surfaces leaving large pits or holes and can eventually eat entirely through a component. It can also weld bolts and fittings to the engine and components.
This can be caused by coolant that is too old or antifreeze mixtures that are not close to 50%.

A Digital Multi-meter can sometimes be used to test for this.

  1. Attach the DMM ground probe to the negative battery post.
  2. Insert the tip of the positive probe into the coolant and observe the reading.

OK - less than .10 volts.
Bad - anything above .20 volts.

The lack of voltage at the coolant doesn't mean the old coolant is good. The voltage can vary by coolant temperature, how long a car has been driven and other factors. It can be OK at times but rise during a hot drive when the temperature is too high to test.

There are also other properties of coolant that degrade and cause problems long before electroalysis is present. Old coolant that has had its additives depleted causes radiator and heater core tubes to start get restricted from corrosion and rust and scale buildup which won't show with a voltmeter test.

Corroded water pump New water pump
left picture is from a badly eaten away water pump impeller because of very old coolant. The picture on the right is a new pump for the same vehicle. The old water pump was no longer able to pump water and the electrolysis had also taken out the timing cover gasket.

Electrolysis destroyed this head gasket. It started leaking from a coolant passage to the outside of the engine after the material was eaten away.

Antifreeze Concentration Chart

Antifreeze Concentration Chart

Coolant Leaks and Coolant Types

Good reasons to bring your Car, SUV or Light Truck to Wayne's Garage

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