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Subject: Honda Coolant/Anti-Freeze
Recently, several people have questioned whether the coolant (anti-freeze) sold by Honda dealers is different from the popular mass-market brands.
Honda has sent the information attached below to its dealers. While you might not expect the source to be exactly unbiased, it does provide technical information and justification for differences in their formula.

Genuine Honda Coolant is the Only Way to Go
Increasingly severe operating conditions and the advent of lower maintenance requirements have resulted in significant changes in the variety and the concentration of additives used in engine coolant. Also, the continual improvements in engine and vehicle design have challenged coolant suppliers to design products that perform well in a more demanding environment.
To meet these needs, Honda engineers have developed a superior, high-quality coolant that has several advantages over the competition.
Some antifreeze, although labeled as safe for aluminum parts, may not be compatible with Acura cooling system components. Extensive research and testing by both Honda R&D and CCI, the manufacturer of the Honda coolant, have proven that the abrasive silicates and/or borates found in most domestic coolants can cause these problems:
- Silicates bond to the surface of the water pump seal and act as an abrasive, causing considerable seal erosion and coolant leakage. In actual tests, the silicated coolant caused early leakage. This leakage increased dramatically until a substantial portion of the coolant had been lost. In contrast, the Honda coolant had almost no leakage through the duration of the test.
Chart here, entitled "Coolant Leakage from Water Pump Seal", showing Leaked Coolant Volume in ml as follows for each test duration in Hours:
24 hrs: Honda Coolant 0, Typical Silicated Coolant 21 48 hrs: Honda Coolant 1, Typical Silicated Coolant 36 72 hrs: Honda Coolant 2, Typical Silicated Coolant 47 96 hrs: Honda Coolant 2, Typical Silicated Coolant 55 120 hrs: Honda Coolant 2.5, Typical Silicated Coolant 56 144 hrs: Honda Coolant 3.5, Typical Silicated Coolant 57 168 hrs: Honda Coolant 4, Typical Silicated Coolant 58.8 192 hrs: Honda Coolant 6, Typical Silicated Coolant 63 200 hrs: Honda Coolant 6, Typical Silicated Coolant 64
- Silicates tend to gel and settle in the coolest parts of the cooling system, causing radiator plugging and overheating.
- Borates cause pitting corrosion on the cylinder head.
- Silicate inhibitors are difficult to stabilize and, therefore, limit coolant shelf life.
Most commercially available coolants were originally designed for cast iron engines. Silicate, an inexpensive additive, was added to coolants to prevent aluminum corrosion, but the long-term durability of the combination was not tested.
In contrast, Honda coolant was designed specifically for aluminum engines. It contains an organic corrosion inhibitor instead of silicate. This superior formula gives these advantages:
- No silicate abrasion of water pump seals. For example, these graphs show the surface roughness of two aluminum water pump seal rings. Seal A, exposed to silicated coolant, shows considerable damage. Seal B, exposed to Honda coolant, displays only minute wear.
(graphs here, showing roughness across the surface, with A a very wiggly line, and B a very smooth line)
- No plugging or overheating caused by silicate gelling.
- Excellent corrosion protection for aluminum components.
- Long-term corrosion protection for other cooling system materials (steel, cast iron, copper, solder, gaskets, seals, and O-rings).
(note from XXX - I think I can guess whether the last paragraph, provided below, was written by the engineers or by the marketers...)
You can find less expensive coolants on the market, but now you can see why genuine Honda coolant is the only coolant approved for Honda and Acura vehicles (it MUST be used for warranty repairs). Honda's non-silicate formula delivers added protection not offered by 95 percent of other brands. Since our customers expect lower maintenance, you're doing them an injustice if you use any other coolant.