Cooling system care

Why is it that our heavy-duty cousins can get so much more life out of their coolant fills than we can? It’s not unusual for a Class 8 rig to go as far as 600,000 miles before needing a complete coolant replacement. Yet OEM maintenance intervals for most cars and light trucks (using extended life coolants) top out at around 150,000 miles. And I’d be willing to bet that many shops are recommending coolant replacement every two years or 30,000 miles, regardless of the type of coolant in use.

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How do you perform that service? Do you still offer “drain and fill” as an option or do you perform a thorough cleaning, followed by a flush and complete refill?

Here are a few ideas on how to offer a professional cooling system service to your customers.

Coolant Formulations
The cooling system, and the coolant in it, has some pretty important tasks to perform. The cooling system is fundamental in maintaining the engine’s operating temperature in a specified range. The coolant is the means to transfer that heat from the engine to the radiator, where it can be released to the outside air. And while water alone is a great medium, we all know coolant uses a glycol base to prevent the water from freezing up on those cold winter nights.

Conventional coolants for domestic makes are typically green in color, and use a phosphate/silicate inhibitor package. Problems with the water sources in other parts of the world necessitated slightly different inhibitor formulations. All conventional coolants rely on inorganic inhibitors to protect the internal system passages and cooling system components. These additives work by forming a protective blanket that actually insulates the metals from the coolant. But this also depletes the inhibitor package in a relatively short period of time, requiring replacement every two years to insure the inhibitor package is able to do its job.

Hybrid organic acid technology (HOAT) coolants are OAT formulations with a small silicate charge. They are considered compatible with both conventional and OAT coolants. Recommended service intervals for both OAT and HOAT coolants is set by the vehicle manufacturer but generally every 5 years or 100,000 to 150,000 miles, whichever comes first.

Why, then, do we see coolant related problems at much lower mileages?

Identifying the Need
Maintaining the proper mixture of inhibitors in the coolant is important. But more important is the health of the glycol base. When the glycol begins to break down, it can form a variety of acids including one called glycolate (may produce a solvent-like smell in the coolant). John Myers, senior technical trainer for the FRAM Group (the parent company of Prestone), says, “If the ethylene glycol forms glycolate all the inhibitors in the world won’t help.” Acids in the coolant will do exactly what you think they’d do. They’ll attack seals, gaskets, internal passages and components.

If the pH of the coolant mixture is OK, the next step is to check the coolant concentration. Nearly every manufacturer recommends a 50/50 mixture of coolant and water. Maintaining this recommended mixture is important to both the level of freeze/boil over protection and the level of inhibitors present in the system. Test strips can also be used for this test, but most industry experts suggest the use of a refractometer for accuracy.

(Of course, do not open the cooling system for testing when its still hot and under pressure. Feel the upper radiator hose. If you can compress the hose without first downing a can of spinach (aka Popeye), the pressure is probably low enough to allow the system to be uncorked. To be extra safe, wear gloves and a full-face safety shield.)

Why?
When you have to pull the trigger on an electronic control module, you want to be pretty sure you know what caused its demise so the new one won’t suffer a similar fate, don’t you? Determining the cause of failed coolant is just as important. Odds are that, if you find the coolant too acidic, there is an underlying problem that will soon do the same to the new coolant if not corrected. And that means problems like internal corrosion/erosion of gasket material, seals and metals.

Prestone’s Myers says, “Yes, it (the pH test) will condemn coolant. But it is also a diagnostic tool. You have to find out what caused the coolant to go bad in the first place.” He also tells us that conventional coolants will test normal with a pH in the range of 8.5 to 11.0 while extended life coolants test a bit lower; ranging from 7.0 to 9.0.

More likely, you’ll find the coolant too acidic. This can indicate too much water in the system (verified by the refractometer test), a bad water source, or the remains of an acid-based solvent that wasn’t properly flushed out. It can also indicate the decomposition of the ethylene glycol base.

Now, what caused the glycol to decompose?

Failed radiator caps can be a source of air into the system, but more commonly they fail to maintain system pressure. Lower pressure means a lower boiling point. And boiling coolant causes the same issues as air in the system does. Test the cap and the system for pressure loss with a suitable cooling system pressure tester.

Topping off coolant loss with water or coolant alone is also a no-no. An incorrect inhibitor level can actually accelerate the formation of acids and promote glycol break down. And while we’re on the topic of water, consider that water makes up half of the fill. If your water supply has a high mineral content or is not pH neutral, you can be creating a problem rather than solving one. Water low on calcium, chlorides and sulfates should not only be used for refilling the system, but also for flushing and cleaning it. Nearly every coolant manufacturer offers premixed coolant, eliminating source water as a concern when refilling.

According to Myers, combustion gas leaks into the cooling system are a bigger problem than you may think. This can also cause premature glycol decomposition and the formation of sulfuric acid. Check for leaking head gaskets by looking for visual evidence in the coolant recovery tank, radiator fill neck, oil dipstick and under the oil fill cap. Using a block tester is also a good way to check for combustion gasses in the coolant, and some techs use their five-gas analyzer to literally “sniff out” problems.

Myers stresses that the use of this test is primarily for diagnostics, to help determine the cause of premature coolant failure. Electrolysis can occur for different reasons. In the test procedure just described, we’re looking for weaknesses in the vehicle’s electrical system that might allow current to seek out the coolant as a less resistive current path. It can also cause the inhibitors to precipitate out of the coolant, further reducing protection of the internal co

To properly perform this test, be sure to place the positive probe in the coolant only. Some systems use a sealed radiator and a pressurized coolant reservoir. On these designs, it’s OK to place your probe in the reservoir. Otherwise, go to the radiator fill neck to perform the test. Do not add any new coolant or water prior to the test. Test at the battery first, then at an engine ground, and last at a chassis ground. Perform the test with the key on, but all accessories off. Correct any ground issues found.

Before That Running Test
But before you perform any of the tests we just covered, check for the presence of voltage with the battery totally isolated from the system. Place your positive lead in the coolant, and the negative lead to a good engine ground point.

If the coolant has become acidic, it can cause the cooling system to become a wet cell battery, producing a voltage potential all its own. Normal coolant aging can cause this as can any of the factors we’ve discussed that accelerate that break down. If there is voltage present over 400 millivolts (0.40 volts), service the cooling system and retest. Then you can perform the ground tests outlined above.

Final Notes
Open the hood on a modern car or light truck, and you’ll notice there are often other reservoirs located next to the coolant bottle. There have been cases where washer fluid and DEF fluid was inadvertently added to the coolant, and vice-versa.

Don’t wait just for the annual inspection to come up to test the coolant condition. Anytime your service requires the addition of coolant to the system, perform the pH and concentration tests. If your check finds a coolant system with a low pH or improper concentration, recommend service regardless of when it was last performed. Properly flush all of the old coolant out and refill with clean, fresh coolant mixed properly with good source water.

And always be sure to identify the reason for any premature coolant failure so your service lasts as long as the coolant itself is designed to!

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