Even though the cooling system has a year 'round job to do, it seems that we pay a little more attention to it when the leaves start to turn color and the temperature starts to drop. Not that that has anything to do with the cooling system's role in dispersing excess heat generated by the engine. No, as the mercury starts to drop, our concern is whether or not the coolant is protected from freezing in the block — and that's not a bad starting point for any cooling system inspection!
It's a package deal
The coolant used to protect your customers' engines is similar in all applications in that it is typically a 50/50 mix of water and ethylene (or propylene) glycol.
Why a mix? Water is an excellent medium for removing heat but it provides no protection to the build-up of rust or corrosion in the cooling system passageways or components. It also has a limited operating range, with a freeze point of 32°F and boiling point of 212°F. The development of pressurized cooling systems back during World War II helped raise the upper limit a bit but it did nothing to lower the bottom end, so something had to be added to the water to prevent freeze up. Hence, the glycol.
Ethylene glycol has a freeze point of 10°F and a boiling point of 386°F. The high end is plenty good but the low end is still short on freeze protection when used in extremely cold climates. Alone, it is also less efficient than water at adsorbing heat — about 10 percent to 20 percent less efficient. So, while it appears a better choice than pure water alone (and it is), the use of coolant alone is still lacking and no better as an option.
However, when mixed in a 50/50 proportion, the resulting cooling fluid has a freeze point of -34°F and, with a 14 psi radiator cap installed, a boiling point of 265°F. According to most of the manufacturers’ I spoke with, a working mixture range of 40 percent to 60 percent will still provide sufficient heat transfer while maintaining freeze protection.
What's the best way to test the mixture ratio? Manufacturers agree that the use of a refractometer is the best way to test with coolant test strips coming in a close second. They also agree that the hydrometers of old are not accurate enough to test the coolant mixture and should be avoided.
Still serviceable
If the mix ratio is ok, does that mean the coolant is still serviceable?
We still haven't done anything to protect the cooling system internals from the effects of the water passing through them. An additional chemical package is added to the cooling fluid to protect components and passages from the effects of oxidation and corrosion. This package is called the "inhibitor package" and is generally designed to keep the coolant mixture a tad on the alkaline side, rather than the acidic side. There are three basic types of coolant mixtures; Inorganic Acid Technology (IAT), Organic Acid Technology (OAT) and Hybrid Organic Acid Technology (HOAT). OEMS may require tweaks on the inhibitors for their own models and that's one reason there are so many different combinations and colors on the market.
Now, I don't care if you know an IAT from an OAT or an HOAT. What I do care about is that you understand that these inhibitor packages don't last forever. As they "drop out" or are used up, the coolant becomes more acidic. This leads to leaks in the heat exchangers, damage to the water pump impeller, and erosion of the passageways to the point of internal coolant loss.
What causes the inhibitor package to be consumed? Aging of the coolant is one and that's the reason for the service interval you see in the maintenance schedule. But other factors can speed up the process and if left unchecked or undiagnosed, allow cooling system damage to begin long before that interval arrives. For example, contamination of the coolant (by internal fluid leaks or combustion chamber gasses mixing with the coolant) is more common than you think. One resource I spoke with estimates that nearly half of the vehicles on the road today have leaking head gaskets that can shorten the life of the coolant yet not pose any drivability issues for the consumer other than having to top off the recovery bottle every now and then.
Another common cause of premature loss of the inhibitors is a bad engine-to-chassis electrical ground. Bad ground(s) can encourage current to find its way back to the battery through the cooling fluid and that results in a rapid consumption of the inhibitors.
How do you test the condition of the inhibitor package? Coolant test strips typically include a section that will react to the pH level of the coolant. This is probably the easiest and most accurate way to test outside of having a lab analyze a sample.
Many of you may remember using a voltmeter to measure for the presence of stray voltage in the coolant. The process is simple enough. Attach the ground lead of your meter to the negative battery post and then insert the positive meter probe into the coolant, avoiding contact with the metal in the radiator. If the inhibitor package has been depleted and the cooling fluid has become acidic, the fluid will react with the metals in the cooling system similar to the way sulfuric acid reacts with the lead plates in the battery. It is called a "galvanic" reaction and produces a voltage potential you'll see on your meter face. Anything more than 0.30 to 0.50 volts is indicative of a problem.
A word of caution here, though. The presence of voltage on your meter does not necessarily provide conclusive evidence that it's the acidity level of the coolant that's causing the problem. You may be measuring the effects of that bad ground I mentioned earlier.
Both are bad news and both need to be isolated and corrected. The question you have to answer, through testing, is did the acidity level of the coolant become excessive on its own or is there a bad electrical ground allowing the inhibitor killing current in.
Your inspection process
The first step I want you to take is to review the cooling system description for the vehicle you are servicing in your service information system. Many vehicles today use multiple coolant paths — heck, even multiple water pumps and thermostats!
Next, perform a thorough visual inspection. How much coolant is in the recovery bottle? Coolant doesn't just evaporate — if the level is low there's a reason for it. Be sure to ask your customer, too, if they have had to add coolant with any regularity.
If there is any reason to suspect a leak, look for any visual signs of that next. These can be tough to see, especially if the leak is small. Pay special attention to the area where the plastic side tanks are attached to the radiator's heat exchanger. There is a gasket in there that allows for the thermal cycling of the components and that ages over time. The crimps holding the parts together can only be made so tight and small leaks here are common.
Dye technology has come a long way and the addition of the proper dose of dye may make that leak a lot easier to locate. Just remember a few "best practices". Use the dye maker's specified dosage in the system — no more and no less. Use the UV light that came with the dye kit. It makes a difference as dyes fluoresce differently under different UV wavelengths. And use the yellow glasses to make the dye even more visible. It won't hurt to darken your work area a bit, either.
Don't forget to inspect the belts and hoses while you're at it. Since nearly every accessory drive belt today is a serpentine design made with EPDM and can be worn out well before you see any visual indications, you’ll need a belt wear gauge to perform this check. As for the hoses, the biggest cause of cooling system hose wear is electrochemical degradation, or ECG, and it’s not easy to detect. ECD attacks the rubber from within and is caused by the same acidity developed in the coolant we just talked about.
| The only way to test accurately for serpentine belt wear is with a special gauge, available from nearly every company that makes these belts. The left image shows a good belt, the right a bad one." |
Check the hoses by squeezing them between your thumb and forefinger. The hoses should feel soft and pliable. If they feel tight or crunchy, they may require replacement. Take a close look at the hose connections, looking for signs of softness, bulging (especially when the system is under pressure), or cracks that could be signs of damage caused by ECD or age. Even if the hose appears to be ok, a good rule of thumb is to recommend hose replacement when a hose is over five years old.
Pressure test the system to make sure it can hold the pressure it’s supposed to, and don't forget the cap. Weak caps resulting in lower boiling points can allow the water in the coolant to vaporize, creating air in the system. It can also prevent the normal siphoning of the coolant from radiator to recovery bottle and back again.
Of course, using your refractometer and/or test strip, test the percentage mixture and pH level. If the pH level is ok, the percentage mixture can be adjusted by adding pure coolant or deionized water as needed, but if the pH is out of whack only a thorough flush and refill will do the trick.
A word on water
You may have noticed that there are more and more pre-mixed coolants on the store shelves than there used to be. The reason is simple enough. Water is half the equation and cooling systems are not very tolerant of water that is contaminated before it is even poured into the radiator.
I encourage you to use these pre-mixed solutions to avoid complications caused by bad water. Even the best tap water is aerated to improve the taste and using aerated water is a bad enough idea all by itself. Why would you want to add air to the cooling system right off of the bat?
Not too long ago, I got my hands on a testing tool called a "precipitator." This device passes an electrical current through the water sample and causes any solids in suspension to drop out and become visible. The results were eye-opening! If you must make up your own mixture, use deionized water (first choice) or distilled water (second choice) to not only fill the system but also to flush the system to avoid leaving contaminants behind.
What about universal coolants?
According to an article on the Automotive Aftermarket Suppliers Association (AASA) web site, " Universal coolants typically use a proprietary OAT formula that may or may not contain silicates (to meet the GM requirements), and no phosphates or borates (to meet European and Japanese requirements). Universal coolants can be mixed with ANY type of coolant, including the older traditional green formula coolants, and can be used to refill almost ANY year/make or model of passenger car or light truck. We say almost any application because some experts say a traditional green formula coolant still provides the best corrosion protection for older vehicles with copper/brass radiators."
Others I've talked to say universal coolants can be used but strongly encourage that a thorough flush and cleaning of the cooling system be performed first. And there are those that insist that only the OEM-specified coolant will do. Personally, I'm a fan of the latter but I'll leave the choice up to you.
The important takeaway I want you to leave here with today is that regardless of the claim on the bottle that the coolant inside is a "lifetime" fill, understand that the longevity of the coolant is impacted by the conditions it lives in. Missed leaks (internal or external), bad radiator caps, weak electrical grounds and other factors can all speed up the depletion of the inhibitor package each coolant formulation uses. And once it's gone, the interior destruction can begin.
So test your customers' coolants, not just for the pre-winter prep, but every time they bring it to you for service. It will add revenue to your bottom line and while extending the life of your customers' second largest investment.
