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Cooling System Conditions on Vehicles Equipped with DEX-COOL™
General Motors made DEX-COOL™ Extended Life Coolant standard equipment
in all North American-built vehicles (except Saturn) beginning in the 1996
model year. Some assembly plants made the conversion over the 1995 Memorial
Day shutdown, and all remaining plants were converted for the 1996 model startup.
For the post-Memorial Day built 1995 models filled with DEX-COOL™ and all
1996 models, the coolant maintenance/change interval is 5 years or
100,000 miles, whichever occurs first. In 1997, that interval was increased to 5
years or 150,000 miles, whichever occurs first, which is where it remains today.
Several important factors contributed to the decision for GM to be a pioneer in
the conversion to extended life coolant. The convenience and financial benefit to
the customer of not having to change coolants as often is obvious. Additionally,
the result of having less used coolant to dispose of has the potential to result in
significant benefits to the environment. GM also has realized significant increases
in water pump durability, and radiator and heater core life. DEX-COOL™ is a non-silicated coolant, while most conventional green coolants contain silicates. One undesirable property of silicates is that they are abrasive and over time can contribute to wear of water pump seals, as well as other components. Overall, DEX-COOL™ Extended Life Coolant has performed very well in GM vehicles. However, for a combination of reasons, a few models experience varying degrees of contamination to the radiator cap and/or coolant recovery bottle. In some cases, if the contamination is left unchecked, it can cause problems in other areas of the engine cooling system. We’ll try to assist you in determining the specific type of contamination present, and discuss the most appropriate correction. We’re limiting our discussion to cooling systems that use a drop-center design radiator cap, and a non-pressurized coolant recovery bottle.
The Radiator Cap.
When a cooling system is not full, the air pocket that is created in the radiator
provides a "beachhead" where contaminants can deposit. This occurs much like
sand is deposited by waves on the beach. In cooling systems that use a
drop-center cap and non-pressurized coolant recovery bottle, these contaminants
can deposit in the valve mechanism of the radiator cap. Once the cap becomes contaminated and ceases to function as designed, chances are that the system will begin to lose additional coolant more rapidly. This is because once the radiator cap fails to hold pressure, a 50/50 mix of coolant and water will boil at 226 degrees Fahrenheit, instead of 265 degrees Fahrenheit, at 15 PSI. By boiling at a lower temperature, it is much easier to exhaust the capacity of the coolant recovery bottle as the coolant expands through the failed cap at the lower temperature. When the system cools off, less coolant will then be available to be drawn back into the radiator. After several cycles under these conditions, the level of coolant in the radiator can be significantly reduced and the coolant recovery bottle will be empty.
It is for this reason that the condition and functional ability of the radiator cap is
so important. Always test the functional performance of any radiator cap whenever
cooling system performance is in question, and replace any cap that does
not hold the specified pressure. When removing a radiator cap, be sure to wipe
off all sealing surfaces prior to replacement, in order to ensure a proper seal.
There are only a few models where the system design appears sensitive to this type of contamination. Although the contaminant may be similar looking, different models usually have different recommended repairs. That’s because the makeup of the contaminant is often characteristic to a model or engine family. Because of this, each model should be carefully evaluated to assure the appropriate repair is being made.
The most effective method of preventing, minimizing or eliminating the affects of contaminants is to always maintain the cooling system (including the recovery bottle) at its recommended full level and ensure the radiator cap is functioning properly.
S/T Truck Equipped with 4.3L V6
Bulletin 99-06-02-012B outlines the most effective repair for this model. The contaminant has been identified as i ron oxide, and the cleaning material
recommended in the bulletin was selected because it was proven to be the most effective at cleaning this type of contaminant. It is very important to follow the steps outlined in the bulletin precisely. Cases where the procedure was not effective have almost always been traced to substitution of another cleaning material or the procedure was not strictly adhered to. The most common mistakes have been:
1. Running the flush while the engine operating temperature is too low. Heat acts as a catalyst in this procedure, and if the temperature of the system is not maintained according to the bulletin specifications, the cleaning will not be effective.
2. Failing to correctly assess the level of contaminants in the radiator before
beginning. NOTE: As stated in the bulletin, it’s important to determine if coolant is able to flow through the third row down from the top of the radiator. If not, the radiator core must be replaced before the flush procedure. This is because the cleaner must be able to flow past the contamination in order to clean it. In cases where the system can’t achieve sufficient flow around the contaminants, the cleaner
cannot be effective. Bulletin 00-06-02-004 describes the appropriate repair procedure for the issues most often seen on these models. Although similar in appearance to the S/T issue, the material on the radiator caps of these models contains no iron oxide. It is much more gelatin-like in texture and is usually comprised of sealer pellet residue, hose material and/or other contaminants.
It is very rare to see cases where the contamination evidenced on these radiator caps has spread beyond the radiator neck. If contamination is suspected beyond the
radiator neck, you may choose to remove the radiator end tanks for further inspection. Replacement of the radiator cap, wiping out the radiator neck and topping off the system is all that is normally recommended for these models. Unless other symptoms are present, it is not necessary to flush the cooling system or replace the coolant on these models before their published maintenance/change interval.
2000 LeSabre and Bonneville Equipped with 3.8L V6
Concerns on these models typically center around what is perceived as discolored coolant (usually dark and rust colored in appearance) and a ring of contamination around the inside of the coolant recovery bottle. Analysis has determined that both
of these consist of excess sealer pellet material that was inadvertently installed at the assembly plant. Sealer pellet installation has since been discontinued on these models. Cleaning the coolant recovery bottle, topping up the system and checking
the cap for proper function is all that is required on these models. Finally, as stated in bulletin 99-06-02-012B, the radiator cap is not a good indicator of the general condition of the cooling system. Typically the underside of the radiator cap will
exhibit a greater amount of contamination than the rest of the system, due to the "beach" effect described earlier. Likewise, the color of the coolant is also not a good indicator of its general condition. Due to fading of the dyes used with DEX-COOL™, the coolant in some vehicles may appear pink after time. The addition of sealer pellet (stop leak) material can turn the coolant color to dark red or maroon. As a rule, color alone is not an indication of the quality level of the coolant and does not affect its performance. When performing repairs for S/T trucks, U vans and W cars, it may help to replace the standard radiator cap with a Standt model 10230 or 11230 radiator cap. These caps have a spring center design that may be less sensitive to the effects of low coolant contamination. You should also top off the radiator and
fill the coolant recovery bottle to the hot mark when cold. These measures will combine to guard against the vehicle operating with the cooling system low on coolant. Inform the customer to check the level of the coolant recovery bottle regularly and to maintain it at the proper level by adding a 50/50 mix of DEX-COOL and water whenever it’s found to be low. DEX-COOL™ continues to perform extremely well in the majority of GM vehicles, and has provided a competitive performance and environmental advantage. Other manufacturers are recognizing these benefits. At present, in addition to all North American-built GM vehicles, Texaco extended-life coolant (DEX-COOL™) technology is either in use or approved for use by several other European and North American manufacturers. For those vehicles that may potentially be affected by contamination, the most effective method of eliminating any risk of the contaminants is to maintain the cooling system (including recovery bottle) at its full-recommended level, and ensure the radiator cap is functioning properly.
