Motor Magazine has a new article up. The old one was very good, but this is worth a read... http://www.motor.com/article.asp?article_ID=1655 "Advertising claims by some antifreeze producers to the contrary notwithstanding, these OATs—certainly DexCool—are not universal coolants. You should use them only in General Motors products, VW/Audi through the 2009 model year and Ford vehicles where the reservoir label says so. " Cooling System Service By Paul Weissler | August 2010 Download PDF If you’re looking for a ‘one size fits all’ strategy, your best bet is to stick with tube socks and steer clear of modern cooling systems. These systems won’t tolerate substitution of inappropriate or—worse—incompatible coolants. In all the years we’ve been reporting on cooling systems, we’ve never seen the antifreeze situation more confusing. While the dye colors being used seem to have exhausted the rainbow, we hope most technicians have learned that the color of the antifreeze dye has nothing to do with the corrosion protection formula for the ethylene glycol-based fluid. At each individual car manufacturer, the procedure is to change the dye color of its assembly line coolant when the formula is changed, although Honda changed from dark green to dark blue while retaining the same formula. The what-to-use issue became even cloudier this year as Ford began a multiyear changeover to a single worldwide antifreeze. It had a choice of three formulas that it’s currently using on domestic products. We’ll spare you the suspense: Ford is moving to the orange-red OAT (organic acid technology) antifreeze/coolant it uses in all of its European vehicles, and that tells you that even more Ford of Europe engineering is coming here. At present, we have the Transit Connect panel van imported from Turkey, and the Fiesta economy car, engineered in Europe, that’s being built for the North American market in a plant in Mexico. Ford’s coolant reservoir labeling adds to the confusion. The label on the 3.5/3.7 V6s on the Lincoln MKT says “no orange,” even though Ford is in the process of converting to it. It’s not the current factory fill, and Ford doesn’t want the present OE protection formula adversely affected. The new F-Series heavy-duty models have two new U.S.-built V8 engines—a 6.7L diesel and a 6.2L gasoline version. The new Mustang also has a new gasoline V8—5.0L, to go with the 3.5 V6. These new engines are factory-filled with the OAT coolant. And in case you’re wondering, that OAT is a DexCool clone—basically what General Motors has been using since 1996. One worldwide coolant makes a lot of logistical sense, and even saves Ford some money. But using an OAT coolant does require a lot of specific engineering, as GM learned, so Ford is going slow. The company actually will phase out engines (such as the 4.6 and 5.4 V8s) rather than attempt to convert them from the yellow dye hybrid OAT (H-OAT) it has been using in most of its domestic products since 2002. This go-slow approach should tell you that, beyond any doubt, you shouldn’t use an OAT coolant in any Ford product for which it was not specifically engineered. That’s not our statement (although we believe it); it’s from Ford, and for good reasons. Also, don’t use it where it may eventually go—for example, in the 3.5/3.7 V6s. Advertising claims by some antifreeze producers to the contrary notwithstanding, these OATs—certainly DexCool—are not universal coolants. You should use them only in General Motors products, VW/Audi through the 2009 model year and Ford vehicles where the reservoir label says so. After all, if it didn’t matter, Ford would put an OAT antifreeze in all of its engines, including the 4.6 and 5.4L V8s. Obviously, it does matter. Furthermore, you should use an antifreeze that isn’t just compatible with what’s in the system, but one that has a similar inhibitor formula (mimics it), so the inhibitors in there are boosted, rather than diluted by something else. As a result, the only recommendations we cite are in that category. For example, we wouldn’t advise an Asian formula that didn’t contain phosphate, or in most European cars (OAT-fills excepted) an antifreeze that didn’t contain silicates. Nor would we consider a conventional American green formula with both silicates and phosphates for those vehicles whose formulas contain silicates or phosphates. Here’s the background on these recommendations and the issues behind them: Silicated H-OAT antifreeze uses the popular inorganic inhibitor silicate, which not only protects aluminum very well, but also provides fast protection. That’s particularly important in case a water pump cavitates (imploding coolant bubbles that pockmark the chamber). When left unprotected, the pockmarks corrode, causing the pump to fail). The organic acid is called benzoate, and its effectiveness in combination with silicates is well established. The antifreeze inhibitor package also contains a copper/ brass inhibitor, either BZT (benzotriazole) or TTZ (tolyltriazole), to protect any small copper parts used and any service parts that may be installed later. Ford has used this silicated H-OAT formula since the 2002 model year, Mercedes even longer (over 20 years)—it’s the yellow OE coolant, the aftermarket equivalent being Zerex G-05 or Havoline Custom Made. Chrysler also uses it, but the OE stuff has orange dye, so don’t confuse it with DexCool. This silicated H-OAT antifreeze also contains nitrite, which enables it to protect diesels against cylinder liner vibration-caused pitting. That’s one thing Mercedes likes about it, as does Chrysler for its Cummins diesel engines. The third coolant also is an H-OAT, but this one—preferred by Asian carmakers—uses phosphates instead of silicates. Phosphates quickly reprotect a cavitation-pockmarked pump, plus the Asian makers use BZT or TTZ to protect copper/brass. In Ford and Mazda products, particularly the 3.5/3.7L V6s, the dye is deep green. Other Asian makers may have pink dye (Toyota/Lexus) or blue (Honda). The organic acid is sebacate, as Asian makers refuse to use the chemical ingredient ethyl hexanoate (2-EHA), primarily because it affects gasket materials. They also dislike silicates because in some tests they run, silicates form a gel that could plug passages. Gel formation and plugging is not particularly a real-world issue with the low silicate content in the silicated H-OAT antifreeze. In fact, the only cases we’ve seen where there was real plugging (as opposed to relatively minor deposits) were with higher silicate content in older antifreeze formulas. And even that gel-plugging was rarely seen, unless a vehicle had been sitting unused, in which case the silicates may have dropped out. Silicate dropout, however, also may occur if the antifreeze has been sitting on the shelf for a few years or more. For overall protection, though, silicates beat phosphates. But to maintain the original Asian antifreeze protection, you want the phosphated H-OAT. There’s finally an aftermarket formula you can buy—Zerex Asian Long Life. The dye color is a shade of pink, but it matches up well chemically with all the Asian vehicle antifreezes, regardless of color. In fact, it’s the same formula that’s used by Hyundai, despite the different dye color (Hyundai’s is blue-green). No antifreeze is perfect, and that certainly includes an OAT. The OAT contains 2-EHA, and usually in combination with sebacate. So the formula is these two organic acids, plus TTZ for copper/brass. OAT antifreezes last a long time, but also take a long time—about 5000 miles—to establish protection for cooling system passages. And the slow action means they can’t quickly protect water pumps that are pockmarked by cavitation. So the pump and cooling system must be engineered to minimize cavitation, which is primarily a high-load issue. The chemical 2-EHA causes leaks in silicone rubber gaskets and Nylon 66 gasket carriers, so they must be avoided. Because OAT antifreezes protect best when the system is absolutely full, which means the coolant is in contact with the walls of the system, maintaining a full fill becomes another issue. This is particularly important with cast-iron engine blocks, where a low level causes rust “blushing” on cooling system walls, a pickup of the rust from coolant flow and deposits in the radiator (see the photo on page 26). Although Ford cars have all-aluminum engines, the Super-Duty F-Series truck has the new 6.2L gasoline V8 and 6.7L diesel V8, both with cast-iron blocks. Low coolant level also can affect aluminum heads, so always check the coolant level whenever a vehicle is in for service. If it has a pressurized reservoir, you can check that level easily. If the pressure cap is on the radiator, remove it to make sure the system is topped up; a high level in an atmospheric reservoir doesn’t guarantee the system is full. Ford designed all of its European engines to minimize water pump cavitation, and where possible, it did the same on its U.S. engines (the 3.5 and 3.7L V6s and the I-4s), so they could live with the OAT antifreeze. No such luck with the 4.6/5.4L V8s, which, along with the gasket issue, is why they continue to have the silicated H-OAT until those engines are history. Ford has been particularly sensitive to guarding against low coolant level, which was responsible for the rust “blush” plugging of radiators on some GM cast-iron V6 and V8 engines. Most Ford engines, not just the cast-iron types, have cylinder head temperature sensors, and in some cases on engines already equipped with coolant temperature sensors and even low-coolant-level sensors in the reservoirs. Ford in particular uses the head sensors, for a low coolant strategy that puts the engine into a limp-along mode to protect against warping or worse. Ford also was alert to the cylinder liner pitting issue. You can’t use nitrite in the OAT formulation—it’s a bad mixture. So the new 6.7L diesel was engineered to minimize piston slap. The small amount of protection an OAT coolant provides will be enough to prevent liner pitting, Ford says. An important service lesson, in addition to continuing with whatever is the Ford OE antifreeze: Service parts could be an issue, particularly water pumps and those gaskets that seal coolant passages. Many head gaskets, for example, have silicone sealing rings for the coolant flow holes, and you wouldn’t want to use them for engines with an OAT coolant. Ford has all-metal gaskets for the OAT-equipped engines, Motor was told. Aftermarket suppliers have been alerted to the water pump (design for minimum cavitation) and gasket issues, and the reputable ones surely will engineer appropriate new parts. However, you just might get an aftermarket gasket that was made for the 3.5/3.7 V6s before the coolant change, and if it were made with silicone rubber (or with Nylon 66), it might create a service issue when Ford changes the V6 to an OAT coolant. So a coolant-passage-sealing gasket for a Ford engine that has been changed over to an OAT antifreeze should be an object of caution, if the gasket has been sitting on a parts jobber’s shelf for years. Ford is not pushing the service life envelope very much with the OAT coolant. It’s 6 years/100,000 miles for the factory fill and every 3 years/50,000 miles thereafter. On the new diesel it’s 6/105 for the factory fill in “normal” service and just 2400 hours/60,000 miles in “severe” service (lots of idling, heavy loads—the usual truck stuff). The diesel service interval thereafter is just 3 years/45,000 miles in “normal” service, but 1800 hours/45,000 miles in “severe” service. A likely reason for the shorter service interval after the factory fill is replaced is that Ford uses deionized water for the 50/50 mix on the assembly line, and although it would like to see the aftermarket do the same, it obviously isn’t taking bets that will happen. Because an OAT coolant takes about 5000 miles to establish protection, using pure water for the factory-fill mixture obviously helps protect the system until the mixture has done its job. But we also would note that antifreeze lasts longer if the water with which it’s mixed is free of minerals and other content. You also can use distilled water for service, if that’s easier to get. A gallon jug is maybe a buck or so, and we think it’s a great investment for any well-maintained cooling system. It’s also a plus to which you can point proudly when you hand a customer the bill and explain why your shop does a better job.