Keeping Your Cool

Engine seals aren’t perfect. Impurities get into the cooling system and cause corrosion and scaling. Supplemental coolant additives, also known as SCAs, or the organic acid used in extended-life antifreeze forms a layer of chemical protection on the metal surfaces, but the protective layer decomposes as the engine runs. If it isn’t replaced by good maintenance, you’ll have major engine trouble.


Tap water contains dissolved minerals. The SCAs and the organic acids that protect the cooling system have to be dissolved in water to work. With minerals in the water, the SCAs and acids won’t dissolve. And if they don’t dissolve, they will form a destructive grit that causes trouble with water pump seals.

Consult your owner’s manual for tolerable levels of impurities and the pH value (acidity) of approved water. Then, either buy distilled water that passes all the tests or have your tap water tested at a dealer or laboratory so you know it’s OK. Buying pre-mixed antifreeze and water solves this problem.

The ideal antifreeze mix is 50/50. If you feel you need a higher concentration to give enough freeze protection, observe OEM recommendations for the maximum percentage. Antifreeze in too high a concentration won’t cool the engine correctly.


Use low-silicate antifreeze approved for use in heavy-duty diesels. Coolant meeting ASTM 4985 standards is OK for most engines, but you’d need to add SCAs right away.

The smart thing is to use a fully-formulated ethylene-glycol coolant that meets the TMC RP-329 standard. For propylene-glycol, the designation is TMC RP-330. Some manufacturers, such as Detroit Diesel, recommend using only fully-formulated. As initial fill, fully-formulated gets you started on the right foot. Using it to top off leaves the system perfectly balanced – an approach that makes using anything else seem complicated.


The first cooling system management problem is controlling what goes back in when a little leaks out. Make sure you know what kind of coolant is in your engine and replace only with the same kind. Unless you’re using organic acid technology, it’s ideal to add only fully-formulated, 50/50 pre-mix. Failing that, add fully-formulated coolant and mix with clean water, preferably distilled, in the right proportions. The ideal solution is to carry the right replacement coolant, pre-mixed with approved water, on your truck. Coolant concentration may also change as some types of hoses will let water out but retain glycols; in those cases, you need to add approved water.

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The second problem is that the additives deplete in protecting the metal parts of the cooling system, though organic acid depletes very slowly. The SCAs in conventional coolants, mainly nitrites and nitrates, deplete at a rate affected by how the engine is used. The only way to determine how fast the SCAs will break down or when you should add them is by testing.

“The truck owners who test the coolant regularly have the best luck with the cooling system,” says David Strauss, an instructor at the North American Institute for Mack and Volvo.

Why? Because too little SCA means corrosion and clogging, while too much creates that damaging grit.

Unless you’re using extended life coolant, it’s best to buy what Strauss terms a three-way test kit, which tests the percentage of water vs. glycol, the level of SCAs and the pH. Caterpillar recommends the use of a refractometer, a device that uses light to read the level of either type of glycol. Two-way test strips don’t test that all-important pH, but you can have that done through a dealer.

Polymetric band hose clamps are installed and then exposed to a heat gun to tighten. The material contracts when cold, tightening the grip on the hose and connection.


You may have noticed that your cooling system connections drip a little when the engine gets cold. The reason for this, says Ken Bridges of Gates Rubber, is that rubber expands and contracts eight times faster than iron and other materials used to make connections. So when it’s cold, the hose gets thinner, the connection gets smaller, and the clamp loses its ability to squeeze tight.

The metal clamps normally used are the constant dimension clamp and the constant tension clamp. The latter normally is spring-assisted. Gates’ testing shows that it works better because it contracts with the hose.

Even more effective is a polymeric band that contracts when cold, holding the tension.


Check your operator’s manual for test intervals, which are usually 15,000 to 20,000 miles. The pH should be between 8.5 and 10.5, Strauss says, but if protection fails and pH drops below 8, it must be replaced.

If the SCA level is low, there are two remedies. You can buy SCAs in a jug and just pour them in, or you can buy a cooling-system filter that adds SCAs.

You can change a filter with a maintenance charge of SCAs at recommended intervals, often every oil change. But you can also use a need-release filter, which uses a membrane or special additive chemistry to measure what’s needed.

“The Power Cool need-release filter used with Detroit Diesels automatically adds protective chemistry only as needed, reducing the concentration of dissolved solids and extending the life of antifreeze,” says Ed Eaton, president of Amalgatech, a fluid research and testing company.

Need-release filters typically have a change interval of 18 months and 120,000 miles, Eaton says. Dave Brisk, a business manager at Fleetguard, adds that these filters contain a very fine, synthetic medium that does a better job of getting debris out of the system. Both experts say that because these filters adjust the rate at which SCAs go in, fewer solids are left over. So instead of having to drain at 200,000 to 240,000 miles, you can use the coolant for 600,000 or more miles.

Strauss reports that Mack has a maintenance-type filter with a standard replacement interval that varies from 30,000 to 50,000 miles, depending on the duty cycle (hours also figure in). Follow manufacturer’s guidelines when changing these filters, but you should also test.

For coolant temperature and other details, follow the directions on the test strip container. Once you get the SCA reading, typically something like 800 to 1,200 parts per million, you need to determine the number of containers of SCAs to add by following directions in the OEM maintenance manual. Get the right size containers for the cooling system’s capacity. You’ll add two for a low level, one for a moderate level and, when the level is high, nothing. Change the maintenance filter only if the reading is low enough. If the concentration is extremely low, you will have to change the filter and add a container of SCAs. Always match the size of the filter to the engine’s coolant capacity.

Note that with need-release filters, these routine tests become little more than insurance. Unless somebody has been adding the wrong coolant or something goes wrong with the filter, you’re not likely to have to do anything till it’s time to change it.

Above all, make sure not to add SCAs both via a maintenance filter and other containers. And if you are using a need-release filter, don’t replace it with the wrong filter, add SCAs from a bottle by mistake or change it before it’s time.


When using standard coolant with SCAs added manually or with maintenance filters, the change interval varies from about 150,000 to 240,000 miles, depending on the OEM and whether you use fully-formulated antifreeze. When using need-release filters and fully-formulated coolant, the interval is 600,000 miles. With extended life coolant, the interval is 300,000 to 600,000 miles, and most manufacturers accept the longer limit.

Fully-formulated coolant with need-release filters, say Eaton and Brisk, can last to overhaul, even if that’s 900,000 or 1 million miles. Lab tests verify the safe use of the coolant to those mileages.

Rae Baum of Caterpillar adds that although the normal Cat change interval with extended life is 600,000 miles, users can employ Caterpillar SOS Level 2 Coolant Analysis to maximize the interval.


Either extended life or fully-formulated with a need-release filter will save money over the traditional system of adding SCAs, even though extended life costs more per gallon. Why? Because the traditional system requires a greater volume in flushing and refills at about one-third the mileage.

The makers of need-release filters argue that extended life can cost more when a lot of coolant is lost or brand availability is a problem.

Baum argues that with the Cat EC-1 designation, widely available in several brands, you should be able to refill with a compatible product and preserve the system’s integrity. In the case of exceptions, you might lose extended life’s simple protection and have to change early. Because extended life costs more than fully-formulated, a lot of leakage could end up costing more. Users who can find Cat EC-1 coolant where they run and have minimal leakage argue that extended life’s simpler maintenance saves money.

Whatever system you use, make sure you stay on top of its maintenance. Otherwise you’ll be in for some big repair costs down the line.

Whatever system you use, make sure you stay on top of its maintenance. Otherwise you’ll be in for some big repair costs down the line.


The job of maintaining coolant protection is simplified by new extended-life coolants. These use organic acid technology to protect the cooling system. Texaco (now ChevronTexaco) and Caterpillar jointly developed the idea, and it’s now Cat’s preferred coolant. It is also marketed under the Shell Rotella and DDC Power Cool Plus brands. After a few seal problems, this coolant is accepted for use in Cummins diesels.

Fleetguard has a competitive hybrid organic acid technology called ES Compleat. It uses a need-release filter and relies partly on SCAs.

Organic acid depletes so much more slowly than SCAs that there is no need to measure concentration. If changing from conventional antifreeze, you must first properly flush the system. You then fill the system with pure extended life coolant. Finally, you either remove the cooling system filter and plumbing or replace what’s there with a filter that has no provision for adding SCAs. Caterpillar recommends removal to eliminate potential leaks and the chance of installing a filter that will add SCAs.

Make sure to add only extended life in the proper proportions when there’s a leak. After 300,000 miles, add a jug of extender. Make sure the size of the bottle matches the capacity of your cooling system. Then, go another 300,000 miles before draining. A few OEMs recommend different mileages for the addition of extender and the change, so check the owner’s manual.

Testing is done only to make sure the system has not been contaminated with plain water or with other coolants. The biggest key to making this technology work is ensuring that you add only extended life coolant. Rae Baum, a Caterpillar engineer, reports that Cat developed the industry EC-1 specification for extended life coolants, which required field testing as well as bench tests. EC-1 is available in several brands, so it should be easy to find in a truck stop.

Fortunately, if you do put in standard coolant, it won’t cause damage. But as the concentration of standard coolant passes 10 percent, it will defeat the protection. You could keep the system going by just treating with SCAs. Or you can simply flush and start over.

What do you think about this article? E-mail [email protected].

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