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“Understanding radiator cap and cooling system contamination”

A Review of GM’s DEX-COOL® Video
by John Brunner
Appeared Jan/Feb 2001 Cool Profit$ Magazine
© 2001 All Rights Reserved

While most conventional “green” coolants contain silicates in their inhibitor chemistry, DEX-COOL is a non-silicated coolant. General Motors first started installing it at some of their assembly plants after the 1995 Memorial Day shut down. With the exception of Saturn, the rest of the 1996 models were filled with DEX-COOL following the year-end changeover.

Extended life advantage. The recommended change period for those vehicles factory filled with DEX-COOL in 1995 and 1996 model years is 5 years or 100,000 miles, whichever came first. For 1997 models and later the change interval is 5 years or 150,000 miles, whichever comes first.

Inspecting for coolant contamination. General Motors and Texaco engineers obtained the data contained in this report while examining the coolant in about two thousand 2, 3, and 4 year old GM returned lease vehicles. Note that though the engineers did observe limited coolant contamination in certain models, the vast majority of them were contaminant free.

The culprit: low coolant! All vehicles that showed contaminated cooling systems shared one common condition: low coolant. Low coolant level in the radiator allows a “beachhead” type of deposit accumulation in much the same way that ocean waves deposit sand on the beach. This material can collect on the drop-center valve at the bottom of the radiator cap and prevent it from sealing. Without that seal, the coolant boiling temperature is reduced to 226°F. Sealed to 15 psi, it will not boil before 265°F. The lack of pressure and premature boiling allow an already under filled coolant reservoir to completely empty itself and leave the radiator tank with a substantial air pocket or beachhead. Always test the pressure cap and replace it if it fails to hold proper pressure.

The contaminants. Though all the contaminants looked the same, there were actually three completely different types identified during the examinations: iron oxide, sealer pellets (stop leak) and hose material. Different cleaning procedures have been established for each application.

The vehicles. From their examinations, GM isolated these vehicle models as suffering from cooling system contamination: ST Utilities and Pickups with the 4.3-liter engine, W cars with the 3.1 or 3.4 liter engines and the 2000 Buick La Sabre/Pontiac Bonneville. Below are the procedures to be used for each series.

ST Utilities and Pickups. A small number of ST utilities like Chevy Blazer, GMC Envoy, Olds Bravada, and ST pickups with 4.3-liter V6 engines were found with iron oxide contamination. This problem requires a cooling system chemical flush. For instructions, get a copy of GM Bulletin 99-06-02-012B and follow them carefully!

Since heat is a catalyst, while flushing with the recommended chemical cleaner, be sure to allow the engine to achieve a normal operating temperature. Use a scan tool to accurately measure the coolant temperature. And since the cleaner must be able to flow past the contamination, check to be sure that not more than the two top rows of the radiator’s tubes are plugged. If the coolant will not flow through the third row down from the top, flushing will do no good; the core must be replaced.

“W” cars. A different bulletin applies to “W” cars like Chevy Lumina, Pontiac Grand Prix, and Buick Century, etc., with 3.1 or 3.4-liter engines. The contaminant in these systems is sealer pellet residue and hose material. This issue is dealt with in GM Bulletin 00-06-02-004. In most cases this is a gel-type deposit and is limited to the sealing surface between the radiator neck and the cap. Cleaning (wiping) the surfaces, testing the cap and refilling properly will usually be adequate to solve the problem. Again, read and follow the bulletin!

2000 Buick Le Sabre/Pontiac Bonneville. Finally, the 2000 Buick Le Sabre/Pontiac Bonneville may exhibit discoloration, or a ring of contamination in the overflow bottle. This is usually excess sealer. Sealer pellets are no longer installed during assembly of these vehicles. Remove the bottle, clean it and reinstall. Naturally, test the pressure cap and top off the system with 50/50 mixture. Note that color is not an accurate indicator of coolant condition. Even an off-colored (sometimes pink) DEX-COOL can still provide adequate freeze and corrosion protection to the system.

The Stant 10230 Radiator Cap. Replacing the existing radiator cap on the ST trucks, U vans and “W” cars with a Stant 10230 or 11230 is advised. This spring-center valve design provides extra system sealing protection over that of the drop-center model; it is less vulnerable to contaminants interfering with the seal.

GM suggests that coolant bottles should be filled to the “full” mark when cold. The vehicle owner should be counseled to keep the bottle properly filled with 50/50 mix. These suggestions would appear to be wise for a number of vehicle applications.

There are about 20 million GM vehicles on the road with factory installed DEX-COOL. This study affirmed that in the vast majority of these vehicles, it is truly delivering the promised long service life. Keep the system cleaned and pressurized and any vehicle can achieve that level of performance.           $$$

John Brunner has a BS Degree in Automotive Technology. Recently retired from GM, he is now teaching, writing, and consulting on a limited basis. Phone: 480-969-4307, e-mail jjbrunner@qwest.net.
*DEX-COOL is a registered trademark of General Motors Corporation.

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