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All about Dex-Cool®

The following information has been gathered by myself through contacts in the automotive industry and my personal mechanical experience. I have tested the below information thoroughly to be accurate on my own GM and Daimler-Chrysler vehicles. I also have contacted GM and DC service departments to verify this information and they certify it is 100% accurate as of their October 2002 technical publications.

Dex-Cool (ethylene glycol) is identical to the Chrysler & General Motors factory fill. Havoline had the original patent on Dex-Cool and manufactures it for GM. The benefits of Dex-Cool are:

For optimum year round protection against freezing, boiling and corrosion, a 50 percent Dex-Cool solution (1 part anti-freeze/1 part water) is recommended. For maximum protection against freezing in extremely cold areas a 60 percent solution (3 parts anti-freeze/2 parts water) can be used. Concentrations greater than 67 percent or less than 50 percent are not recommended.

Dex-Cool Physical Properties

If your vehicle came with the inferior green stuff (propylene glycol), you must do a complete and thorough flush before switching to Dex-Cool. Also make sure to stay away from 'organic based' rust inhibitor additives. They originated in Euro/Asian markets and are not compatible with Dex-Cool. These additives may cause gumming of the antifreeze. OEM style additives designed for use with the green antifreeze (propylene glycol) may reduce the durability of Dex-Cool. If you started off with green, GM recommends switching to Dex-Cool in their technical service bulletins. If you choose to continue using green, just check the alkalinity more often. Green will keep you protected thermally just as well as red.

As for deciding when to change your antifreeze, don't go by miles or you WILL certainly have seal and mechanical failures. One interesting spec I found is to use a multimeter. You put your negative probe to the negative post on your battery. You then place the positive probe in the neck of your radiator, making sure that the positive probe touches nothing but the antifreeze. Make sure the coolant is warm but not HOT (this is for SAFETY reasons as well as accuracy of your readings. Always be careful when opening the radiator cap on a warm engine). Your readings (regardless of negative symbol on readout) should be:

  • 0.2 V to 0.5 V - antifreeze is still good
  • 0.5 V to 0.7 V - antifreeze is borderline
  • 0.7 V or greater - antifreeze is unacceptable.

You can also use test strips (available at a quality auto parts store for $5 or less), they work on both green and red types too. But if you already have a multimeter, why go buy test strips? The multimeter is the more technically accurate method anyway.

As for sludging and early parts failure, it is imperative that you keep the antifreeze topped off or the low fluid level will cause sludging. There is a GM Technical Service Bulletin (TSB) on this matter. Dex-Cool's extended service intervals are made possible from its patented organic acid corrosion inhibitor system that eliminates the need for silicates, phosphates, borates, nitrites, and amines. Elimination of these additives is significant because many of them are abrasive to water-pump seals.

Another way to ensure longer life of parts and get better corrosion protection is to make sure you USE DISTILLED WATER when mixing with antifreeze. By just using regular tap water you contaminate the new Dex-Cool and drastically lower the corrosion protection. Distilled water barely costs 59¢ a gallon in my area. So there's no excuse for spending $7.99/gallon on Dex-Cool and then ruining it because you're too lazy to add 59¢ a gallon distilled water to it.

For further information on this antifreeze/coolant, I certainly encourage visiting the listed sources below. In particular, you should visit the ASTM site and view the following sources/standards:

  • Chevron Texaco. Website:
  • Havoline. Website:
  • American Society for Testing and Materials (ASTM) Website:
  • USDOT Office of Defects Investigation, Technical Service Bulletin (TSB) search engine:
  • D512 Test Methods for Chloride Ion in Water
    D516 Test Methods for Sulfate Ion in Water
    D1119 Test Method for Percent Ash Content of Engine Coolants and Antirusts
    D1120 Test Method for Boiling Point of Engine Coolants
    D1121 Test Method for Reserve Alkalinity of Engine Coolants and Antirusts
    D1122 Test Method for Density and Relative Density of Engine Coolant Concentrates and Engine Coolants by the Hydrometer
    D1123 Test Methods for Water in Engine Coolant Concentrate by the Karl Fischer Reagent Method
    D1126 Test Method for Hardness in Water
    D1177 Test Method for Freezing Point of Aqueous Engine Coolants
    D1193 Specification for Reagent Water
    D1287 Test Method for pH of Engine Coolants and Antirusts
    D1293 Test Methods for pH of Water
    D1384 Test Method for Corrosion Test for Engine Coolants in Glassware
    D1881 Test Method for Foaming Tendencies of Engine Coolants in Glassware
    D1882 Test Method for Effect of Cooling System Chemical Solutions on Organic Finishes for Automotive Vehicles
    D2570 Test Method for Simulated Service Corrosion Testing of Engine Coolants
    D2809 Test Method for Cavitation Corrosion and Erosion-Corrosion Characteristics of Aluminum Pumps with Engine Coolants
    D3321 Test Method for Use of the Refractometer for Field Test Determination of the Freezing Point of Aqueous Engine Coolants
    D3634 Test Method for Trace Chloride Ion in Engine Coolants
    D4327 Test Method for Anions in Water by Chemically Suppressed Ion Chromatography
    D4340 Test Method for Corrosion of Cast Aluminum Alloys in Engine Coolants Under Heat-Rejecting Conditions
    D4725 Terminology for Engine Coolants
    D4985 Specification for Low Silicate Ethylene Glycol Base Engine Coolants for Heavy Duty Engines Requiring a Pre-Charge of Supplemental Coolant Additive (SCA)
    D5223 Specification for Engine Coolant Grade Propylene Glycol
    D5827 Test Method for Determination of Chloride in Engine Coolant by Ion Chromatography
    D5931 Test Method for Density and Relative Density of Engine Coolant Concentrates and Aqueous Engine Coolants by Digital Density Meter
    D6210 Specification for Fully Formulated Ethylene Glycol Base Engine Coolant for Heavy Duty Engines
    D6211 Specification for Fully Formulated Propylene Glycol Base Engine Coolant for Heavy Duty Engines
    E1177 Specification for Engine Coolant Grade Ethylene Glycol Other Documents
    D1888 Test Methods for Particulate and Dissolved Matter, Solids, or Residue in Water
    SAE HS40 Maintenance of Automotive Engine Cooling Systems
    ASTM MNL 6 Manual on the Selection and Use of Engine Coolants and Cooling System Chemicals

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Page created on 9/22/2002
Last updated on 11/5/2004