Cooling System Issues

Industry experts estimate that about 40 percent of engine downtime is caused by cooling system problems. Understanding the common problems and implementing proven preventative maintenance practices significantly reduces operating costs.  There are four...

- Corrosion of the water pump impellers.

- Thermostat malfunctions.

- Gel insulates fan temperature sensors, causing improper air fan operation resulting in overheating.

- Fouling of the radiator with silica gel of phosphate sludge from the antifreeze.

- Solder corrosion and consequent solder bloom fouling.

- Corrosion of the copper or aluminum radiator core.

- Water pump seal failure due to excess dissolved solids and/or high phosphate levels.

- Water pump cavitation due to foaming.

- Short-outs in block heater due to phosphate scale buildup.


The potential for scale formation on hot metal cooling system surfaces is affected by a number of dynamic conditions, says Martinelli: By way of example: the harder the water being used in an engine coolant, the greater the potential for scale formation. As coolant temperatures increase, hardness salts (calcium and magnesium) in solution have the potential to plate out on hot metal cooling system surfaces.

“Flow characteristics are an important consideration as scale generally forms on the hot side of a cooling system and in areas of low or turbulent flow,” he says. “Entrapped air can also be a problem as any air bubble formation in a coolant area - bubbling around a hot source - increases the tendency for scale to form in that area. High pH will increase the potential for scale deposits as well.”

Lastly, there can be damage to water pump seals.

Calcium and magnesium have the tendency to combine with the phosphates found in low grade antifreeze and some additive packages, explains Martinelli. They form calcium and magnesium phosphate scale on heat transfer surfaces, especially on water pump seal faces.

“These deposits can distort the flatness of a seal face, preventing the water pump seal from sealing. The result can be leaking water pumps.”

There is also the matter of green goo or drop-out, which happens when additives, especially silicates, get too concentrated and drop out of the liquid, forming green goo. This can also lead to water pump failure, as well as radiator blockages and heater core problems.


Now that you know what happens if a cooling system is not properly maintained, what should you look for when checking coolant?

Coolant color is important, Martinelli says, as coolant can come in green, pink, red, blue, yellow, orange and even brown.

“The color of the coolant is one indicator as to what kind of coolant you have and how it is to be maintained. Mixing of technologies and not maintaining them correctly can lead to cooling system problems.

“While coolant comes in many different colors, they have one thing in common: they should all be clear.

If the coolant appears cloudy or has particulates floating in it, this could be a sign of bigger problems. “Clarity is a major concern.”

Properly maintained coolant should have a freeze point of -34 degrees Fahrenheit, warns Martinelli. This indicates there is the proper 50/50 mix of antifreeze and water. 

“Too much antifreeze can lead to water pump failures, drop-out and improper cooling of the engine. Maintain the freeze point between -25 degrees and -50 degrees Fahrenheit for optimum performance.”

Chemical levels also must be maintained and monitored in the coolant, he says. Depending on the type of coolant in the engine, there are different maintenance practices that must be adhered to in order to keep the unit running.

“Coolant is indeed a hot topic these days,” concludes Martinelli. “With all the different colors and chemistries available, it is more important than ever to ensure a proper cooling system maintenance program. 

“As mentioned earlier, an estimated 40 percent of engine downtime is caused by cooling system problems, but take comfort in the fact that cooling system problems are virtually 100-percent preventable.”


Two commonly used cooling system service machines are coolant flushers and coolant exchangers.

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