The keys to cooling system maintenance are simple. Never mix, never worry. And when it comes to coolant, care and consistency matter most.
You need to maintain your coolant for the same reason you change your oil: proper protection. Engines burn fuel, but fuel does not burn perfectly and at least some hostile stuff (like acids) ends up in the cooling system. Why? Because engine seals don’t work perfectly. This contamination causes corrosion and scale formation.
The front line of defense in your cooling fluid are SCAs, Supplemental Coolant Additives.
The purpose of SCAs or the organic acid used in Extended Life antifreeze, is to form a layer of chemical protection against corrosion and scale on the cylinder liners and other metal surfaces in the cooling system. Unfortunately, the protective layer decomposes as the engine runs.
Watch the water
Tap water is contaminated with dissolved minerals. But the SCAs or organic acids that protect the cooling system have to be dissolved in water to work. In fact if they aren’t dissolved, they will form a destructive grit that causes trouble with water pump seals.
Consult your OEM owner’s manual for a table that lists tolerable levels of sulfates, chlorides, iron, and other 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 through a dealer or laboratory so you know it’s OK to use. Many brands of antifreeze come pre-mixed with pure water, which solves this problem.
Don’t use too much antifreeze. The ideal mix is 50/50. If you need to go beyond that, use only as much antifreeze as you need for freeze protection, observing OEM recommendations for the maximum percentage. Remember that while a good mix cools well, antifreeze by itself won’t cool the engine properly.
The chance of mixing the wrong proportions of water and glycol is another reason to just buy pre-mixed.
What kind of antifreeze?
The two basic types of antifreeze used in heavy diesels are ethylene-glycol and propylene-glycol. David Strauss, an instructor at the North American Institute for Mack and Volvo, says the latter is sometimes used where coolants heat trailers that carry food products, as it is less poisonous, and more environmentally compatible in case of spills. Some manufacturers (like Volvo) prohibit the use of propylene-glycol, while others, like Caterpillar, limit its use to a 50/50 maximum because it does not cool as well as ethylene-glycol.
You must use a “low silicate” antifreeze approved for use in heavy-duty diesels. Coolant meeting ASTM 4985 standards is okay for most manufacturers, as it has nothing destructive in it, but you will need to add SCAs. The smart thing to do is to use a “fully-formulated” coolant that meets the TMC RP-329 standard (for propylene-glycol, the designation is TMC RP-330). Some manufacturers, like Detroit Diesel, only recommend the use of fully-formulated coolant. Since choosing fully-formulated as your initial fill gets you started on the right foot, and, when used to top the system off normally leaves it perfectly balanced, there’s usually little reason to consider using anything else.
An unprotected cooling system can allow scale to form on the outside of the liner. By holding heat in, the scale can cause the lube oil to get too hot and thin out. The result can be damage to the piston, rings and liner that looks like a lubrication failure.
A couple of things happen to coolant as it ages. First, the additives gradually deplete as they break down in the act of protecting the metal parts of the cooling system. Second, small amounts of coolant normally leak out of the system and are replaced. The question is: With what? The biggest problem of cooling system management is controlling what goes back in.
Every driver should know what kind of coolant is in his engine, and he should replace only with the same kind. It’s ideal for the driver to carry the right replacement coolant, pre-mixed with approved water, along with him.
Coolant concentration may also change slightly because some types of coolant hoses will let water out but retain glycols. Too much glycol or too much water can easily be corrected with approved water or concentrated (rather than pre-mixed) coolant.
Managing SCA depletion by maintaining the level in the system is another challenge. In addition to the above variables, every engine runs a different duty cycle. The SCA additives used with all conventional coolants, composed mainly of nitrites and nitrates, will deplete at a rate that depends upon how the engine is used. There is no reliable way to determine how fast the SCAs will break down, or when you should add them, except testing. As David Strauss says, “It’s best to test. The truck owners who test their coolant regularly have the best luck with their cooling system.”
Why? Because too little SCA means the system will corrode or clog, and too much creates that damaging grit.
When using SCAs, it’s best to buy what Strauss terms a “3-way” test kit. This tests the percentage of water versus glycol, the level of SCAs, and the pH. Caterpillar recommends the use of a refractometer-a glass device that reads the level of either type of glycol with light. Some engine makers’ test strips don’t test for pH, but you can have coolant tested through a dealer to check that all-important acidity.
Preserving SCA protection
See your OEM operator’s manual for coolant test intervals, most often 15-20,000 miles, although some suggest longer intervals.
One thing SCAs protect against is acidity. The pH should be between 8.5 and 10.5, says Strauss, but if the protection fails and pH drops below 8 (meaning the coolant has become acidic), it must be replaced.
There are three ways to add SCAs to the system (in addition to starting out with fully-formulated coolant). You can buy SCAs in concentrated form in a jug and just pour them in. Or, you can buy a cooling system filter that adds SCAs as the coolant passes through it.
You can change a filter with a “maintenance” charge of SCAs at recommended intervals-such as every oil change or every other oil change. You can also use a “need-release” type of filter. These use a membrane or special chemistry in the additives to ensure that SCAs only leave the filter and enter the system when the fluid’s SCA level is too low and more are needed. These, typically, have a long change interval in the range of 18-months and 120,000 miles, says Ed Eaton president and chief engineer of Amalgatech. Eaton says “The PowerCool need-release filter, used with Detroit Diesels, automatically adds protective chemistry as it is needed, reducing the concentration of dissolved solids and extending the life of the antifreeze.”
Dave Brisk, business manager coolant and chemical products at Fleetguard, adds that these filters contain a “very fine, synthetic media” that does a better job of getting debris out of the system in addition to adding the chemicals gradually. He agrees with Eaton that such a system allows coolant to last much longer.
With these filters there is much less leftover solid material in the coolant from the SCAs. So instead of having to drain at 200,000-240,000 miles to get that solid stuff out of the system, you can use the coolant for 600,000 or more miles.
Strauss reports that Mack has a maintenance-type filter that has a standard replacement interval that varies from about 30,000 to 50,000 miles, depending upon the duty cycle (hours also figure in). It’s good to generally follow manufacturer’s guidelines when changing these filters. But, you should also test. When adding SCAs out of a container, it’s essential to test.
Follow the directions on the test strip container as to coolant temperature and other details to get a good measurement. Once you get the reading of SCA level, typically something like 800-1,200 parts per million, you need to determine the number of containers of SCAs to add. Follow charts in the OEM maintenance manual as to test levels and how much to add. 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 remember to match the size of the filter to the engine’s coolant capacity.
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 change it before it’s time, replace it with the wrong filter, or add SCAs from a bottle by mistake.
Prestone’s heavy-duty “fully-formulated” coolant meets the TMC RP-329 standard.
Extended Life coolants
Extended Life coolants use organic acid technology, sometimes combined with just a bit of nitrites and molybdates, to protect the system. Texaco (now ChevronTexaco) and Caterpillar jointly developed the concept, and Cat now recommends it as the preferred coolant. It is also marketed today under the Shell Rotella and DDC Power Cool Plus brands. After a few seal problems, this coolant is now satisfactory for use in Cummins diesels.
Fleetguard has a competitive hybrid, nitrited organic acid technology called ES Compleat. It uses a need-release type of filter and relies partly on SCAs.
The big difference with Extended Life is that there is no need to measure concentration levels as these additives are much more stable, stay active, and deplete much more slowly. You start out with pure Extended Life coolant (if changing from conventional antifreeze the system must first be properly flushed). You then 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 in order to eliminate potential maintenance concerns and the chance of installing a filter that will add SCAs.) Make sure to add ONLY Extended Life coolant in the proper proportions when there’s a leak. After 300,000 miles, add a jug of Extender. Just make sure the size of the bottle matches the capacity of your cooling system. Then, you can go another 300,000 miles.
Check your OEM manufacturer’s recommendations, because a few recommend different mileages for the addition of extender and the change.
When is it time to change?
When using standard coolant, with SCAs added manually or with maintenance filters, the change interval varies from about 150,000-240,000 miles, depending upon the OEM and whether or not you use fully-formulated antifreeze. When using need-release filters and fully-formulated coolant, the coolant change interval is 600,000 miles. With Extended Life, the interval is 300,000 to 600,000 miles, with most manufacturers accepting the longer limit.
Fully-formulated coolant with need-release filters, say both Eaton and Brisk, can last to overhaul, even if that’s 900,000 or 1,000,000 miles. Lab tests verify the safe use of the coolant to those mileages.
For more information, contact:
Castrol Heavy Duty Coolants
Caterpillar Engine Div.
Detroit Diesel Corp.
FPPF Chemical Co.
Mack Trucks, Inc.
The Penray Companies
Shell Oil Co.