This is kind of a sleepy thread, but I recently came across this on-line supposedly from a Honda communication to dealers:
Honda says this about silicate and borate based coolants and how bad they are for aluminum engines:
Note in their tests they had leakage in a short time with silicate based coolants, not to mention other potential problems they warn against.
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- 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).
