August 2005 Articles & Features

Advance Auto


adjust text size: Cooling System Service Update

By Paul Weissler | August 2005

There's no sense longing for the good old days. Today's cooling system service requires specialized equipment, an understanding of coolant/antifreeze compositions and compatibilities and knowledge of specific vehicle requirements.

In the old days, if a cooling system didn't leak or overheat, we used to ignore it at this time of year. Today, the system has to operate year 'round within very precise ranges, as if it were an emissions control. Well, it is an emissions control, and a cooling system problem can turn on the MIL before it ever illuminates the overheat lamp. In fact, the diagnostics are aimed at finding the engine that warms up slowly, takes too long to go into closed-loop and doesn't run warm enough for lowest emissions.

When that happens, there'll usually be a trouble code, such as P0128, which indicates failure to reach normal operating temperature in a specified time. Often the reason is a thermostat that was removed (and not reinstalled after the system was flushed during the spring).

More often there's a problem because the cooling system hasn't been touched at all, many motorists believing extended-life coolants are a â€œlife of the carâ€ deal they can forget about.

It's no secret that many car manufacturers have been extending coolant service intervals. Reducing maintenance is just fine with motorists who would normally ignore it anyway. And environmentalists like the idea of dumping less antifreeze, even though much of it would be recycled.

But the extended intervals are really a mixed bag, and not everyone has adopted them. General Motors has a 150,000-mile interval, but sets a five-year limit, the same as Ford and Chrysler Group, which have a 100,000-mile limit. Toyota went to a 10-year interval, also with a 100,000-mile limit. Honda has a 10-year/120,000-mile interval. Mercedes really raised the barâ€”to 15 years/150,000 miles.

But these intervals don't apply to older models. Toyota, for example, had a 60,000-mile coolant-change interval through its 2003 models, and Honda recommended 3 years/45,000 miles through 2000. Mercedes began its changeover from four years to 15/150 on some models in 2003, completing it during the current model year.

In the meantime, such high-volume lines as BMW, Nissan and Subaru have not extended their intervals nearly as far. Even Nissan's extended interval (4/60) is a one-shot deal for new models. The second flush & fill is scheduled after 2/30, which is the only interval recommended by Subaru. BMW uses a 4/50 recommendation.

It's important to note that these intervalsâ€”extended or notâ€”are based on a properly maintained system. If the coolant mix is kept at about 50/50 and the system is always topped up, the recommendations apply. Otherwise, all bets are off. Furthermore, the long intervals were validated only with specific antifreeze formulas used by the OEMs. If you change to an antifreeze with inhibitors that provide a different type of protection (such as silicates vs. phosphates or organic acids), the system may not continue to be protected under severe conditions.

System neglect is the big issue, howeverâ€”low concentration from top-ups with water, or a low coolant level. The plain fact is that we're seeing a lot more corrosion damage. Once corrosion builds up in a system, electrolysisâ€”indicated by .3 volt or higher in the coolantâ€”may occur and accelerate deterioration. The most effective cure for voltage in the coolant, except in special cases reported in service bulletins, is an effective flushing of the system, not a string of additional ground straps.

There certainly has been enough publicity about GM's problems with low coolant levels and reduced antifreeze concentrations from normal seepage (and water top-ups). The extended-life antifreezes, particularly organic acid technology (OAT) types like DexCool, protect the system most effectively when the coolant is in continuous contact with the cooling system passages. That means a full system, with a 50/50 concentration.

Sure, you can do a complete coolant change without a machine, but it may take repeated draining and filling, thermocycling and topping off. There are more efficient ways to earn a dollar. Getting 90% of the coolant out (the necessary minimum) is really tough without a machine, even if you drain the engine block, disconnect hoses, etc. On many GM 3.8 V6s, for example, removing the knock sensor will let a surprising amount of coolant drain from the block.

Topping Up the System

As for topping up the cooling system without a machine, or at least a vacuum fill kit, you've got to do a lot more than just fill the radiator and reservoir, then hope that engine thermocycling will clear out the air bubbles. Some engines have two fill necks, maybe one on the radiator or pressurized reservoir and a second on a neck on the engine. On Subaru turbos, there's a pressure cap on a housing with hoses to the reservoir. Even with all the bleed valves opened and a jack under the fill neck location, there are no guarantees that you'll get all the old coolant out. Ask anyone who's ever tried to manually top up such classics as the Toyota MR2, Volkswagen Eurovan and Pontiac Fiero, plus various Nissan vehicles.

Establishing long-life protection with a specific type of antifreeze creates an inventory problem for the independent shop. When coolant service intervals were 5/50 or shorter, a good rinsing of the system made it possible to switch to good old conventional American green. That antifreeze contains two popular inhibitorsâ€”silicates and phosphatesâ€”so it worked in European cars with silicated antifreezes and in Japanese cars with phosphate antifreezes. Now many systems contain the organic acid technology antifreeze/coolants that provide a different type of protection, and work far more slowly.

GM, VW/Audi and some European makers use OAT coolants with no silicates or phosphates. Japanese companies have been moving to an OAT with phosphates, but oppose a key organic acid in GM DexCool. Chrysler Group, Ford U.S.A. and BMW use basically the same antifreeze as Mercedes, a low-silicate hybrid formula.

As another indication of the meaninglessness of antifreeze dye colors, Honda just switched from green to blue, with no change in the formula. If you see an extended-life coolant label under the hood and the coolant is the original stuff, it could be green if it's pre-2005. And we hope you know that despite the orange color of the Chrysler coolant, it's exactly the same formula as the yellow coolant in Ford products, or the usually yellow but sometimes blue antifreeze in Mercedes-Benz models.

Mercedes is an easy-to-understand example of why you shouldn't change types of extended-life coolants. Mercedes' coolant jug contains a silica gel bag (yes, something similar to the packets designed to absorb moisture in camera cases, etc.). However, with a coolant containing silicate inhibitors, the silica gel helps maintain a stable level of silicate protection over the years. Mercedes has long used the silica gel bag, and the protection level is supported by field experience. The packet is built into the jug and is a life-of-the-car item.

Because each extended-life antifreeze provides a specific type of protection, you should stick with the original type. Under severe conditions, such as a low antifreeze concentration, there might not be enough of the needed additives (silicates, phosphates or other inhibitors) to do a good job.

Given the variety of individual vehicle requirements and the specific antifreeze/coolants developed to fulfill those requirements, it would be foolhardy to top off with whatever is handy. Even Texaco, which once promoted its DexCool formula as a one-for-all, has introduced Havoline Custom-Made, a low-silicate formula for Ford U.S.A., Chrysler Gro