Reprinted from i Saluti, May 1999
from Skinned Knuckles (175 May Ave., Monrovia, CA 91016), 

New Long Life Coolant May Not be Good for Old Cars 

by Bill Siuru 

In the March 1996 issue of Skinned Knuckles, I reported on Havoline DEX-COOL Extended Life Antifreeze/Coolant. After talking to a technical expert at Texaco Lubricant Company, I concluded that DEX-COOL could be used in older cars to extend the time between flushing and replacement for up to five years. 

After my article was published, Jay Ross at Applied Chemical Specialties, Inc. (P.O.Box 241597, Omaha, NE 68124) sent me the results of ACS’s research into the use of DEXCOOL in the cooling systems in older cars. Incidentlly, the research was instigated partly because of calls to ACS by SK readers. ACS markets “No-Rosion”, also covered in the article. “No-Rosion” is an additive specifically formulated for extending the life of coolant used in older, infrequently driven cars. 

According to Ross, DEX-COOL is an, excellent product for factory fresh vehicles that never had traditional phosphate/silicate antifreeze in their cooling systems. It is also appropriate for use in older vehicles with completely new cooling system components and which are driven on a daily basis. Ross identifies “some very serious issues with regard to using DEX-COOL in the treatment of older, antique, or classic automobiles.” 

First, the cooling systems -on all older cars have at one time contained traditional phosphate/silicate blends of antifreeze. Thus silicate and phosphate residuals will remain in the cooling systems and continue to break away from surfaces, crevices, and tight areas, entering the new DEX-COOL coolant solution. DEX-COOL is not designed to properly disperse or keep these materials in solution. Therefore, they will seek and adhere to the hottest surfaces within the cooling system, forming scales and deposits. Since the hottest areas are the locations where the greatest amount Of heat transfer takes place, they are the worst spots to have deposits that impede heat transfer. The result is a dramatic affect on cooling system efficiency and performance.  Also since corrosion is most likely to occur under deposits, using DEX-COOL could affect long-term corrosion prevention. 

The only way baked-on residuals and deposits can be completely eliminated is by a rebuild of the entire cooling system, using new parts and acid cleaning parts that are reinstalled. In contrast, the instructions from Texaco for converting a vehicle to the long-life coolant call for draining the used coolant, flushing the entire cooling system once with water, and then refilling with water. Then the engine should be run with the thermostat open and heater on until it reaches operating temperature so water circulates through the entire system. Then the water should be drained, the system filled again with water, and flushed once or twice more until the discharge is clear, indicating that all old coolant has been removed. Also coolant filters have to be replaced.

Texaco emphasizes the importance of removing all used coolant and any residual chemicals and filters before installing its long-fife coolant. ACS’s Jay Ross warns that without a complete rebuild with new or acid-cleaned parts, “99.9% of older vehicles’ cooling systems contain phosphate and silicate residuals.” 

The second problem with using DEX-COOL in infrequently driven vehicles, according to Ross, concerns the completely organic character Of carboxylates in DEX-COOL which make them very good long-life corrosion inhibitors. Unfortunately, being organic, they are consumed by some types of bacteria. The bacteria feeds off the carboxylates, using them as a nutrient, so the corrosion protection that they offer disappears and creates, a potentially serious corrosion problem. 

This is no real problem in daily drivers whose cooling systems regularly operate at temperatures of over 170 deg F., where the carboxylate consummg bacteria cannot survive. However, it is a problem in vehicles not driven regularly or stored during the winter months. 

Finally, in some cooling systems, DEX-COOL may interact with internal materials. For this reason, a recent service bulletin from GM specifically states, “DEX-COOL may be used in 1994 and later Buick models for improved water pump seal performance. It should not be used in 1993 or earlier vehicles because its chemical ingredients interact with internal copper-soldered joints.” 

The bottom line is that by using a carboxylate-based antifreeze such as DEX-COOL in a system that contains residuals from the old antifreeze, you could actually do more damage than good. Probably the best approach is to use a traditional antifreeze, the type the system was designed to use. Then, as discussed in the March article, add the recommended amount of No-Rosion to extend the interval between changes and and flushing as well as to ensure protection while the vehicle sits for extended periods.