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Choosing motorcycle engine coolant

The problem:

Sometimes, even a straightforward thing like adding or changing coolant becomes fraught with potential problems.

Case in point:

Choosing a motorcycle coolant should be straightforward. Motorcycle engines are made of aluminium. It stands to reason that if we chose a name brand coolant that featured compatibility with aluminium as well as 7 or 8 other metals, we'd be safe, right?

Well it turns out that we'd be wrong. At least for Honda motorcycles. Coolants do more than prevent freezing and protect from overheating. They also protect from corrosion. Traditional automotive coolant contains silicates as part of its anti-corrosive additive mix. It appears that silicates (abrasive in nature) damage the Honda water-pump seals. There have been a spate of Honda water-pump failures that typically occur within one year of having replaced the OEM coolant with silicate-based automotive coolant.

What's the solution?

The recommended coolant, at least for Honda motorcycles, is the newer-generation non-silicate-based coolant. I suspect that non-silicate coolant would be gentler on other brand motorcycles as well.

This is sometimes an inconvenience for someone not living reasonably close to a Honda bike dealership. In addition, OEM motorcycle dealer pricing tends to be a little higher. After more research, I ended up buying Honda coolant from my local Honda car dealership. This is not only convenient, but probably a little cheaper to boot!

The product name is Type 2 coolant (as opposed to Type 1 that is silicate-based) and comes in a 4 litre jug. It's a long-life coolant, comes pre-mixed, is greening in color, and contains no silicates. I found the price reasonable and that's what I put in. Apparently it is also available in concentrated form. While it may be cheaper in concentrated form, I found the convenience of the pre-mix version to more than make up for any possible difference in price.

There are other long-life coolants out there that contain no silicates. It seems that Dexcool (GM) has a checkered history and may be involved in several class action suits. Dexcool has been linked to possibly serious problems, sometimes turning into a jelly-like sludge. It has also been linked to failed intake manifold gaskets.

There are enough well-publicized doubts about Dexcool in its applicability for automotive applications that I’d be wary of using it in my motorcycle's engine.

Considerations:

Just a heads up re switching to a non-silicate (ie organic-based) coolant.
If you've been running regular silicate-based coolant, you want to ensure a complete flush ie get it all out.

It seems that silicate and non-silicate-based coolants don't mix well. In fact, they're considered non-compatible. It appears that even a small cross-contamination will impact protection.

From what I've gathered, two things happen.

  • the coolant performance is deemed to revert back to the lowest one ie
    a long-life coolant is deemed to revert back to normal life ie 1 or 2 yrs.
  • there seems to be chemical incompatibility between the two, resulting
    in corrosion inhibitors falling out of suspension. It's believed that the acids in the organic
    non-silicate coolants will tend to cause residual leftover silicates to fall out of
    suspension. Apparently, this will affect corrosion protection and possibly add
    (how much I don't know) to silicate-caused negative results.

re type of water to use:

Regular, mineral-rich tap water encourages scale build-up. Minerals tend to deposit as scale and do so more easily at high temperatures. This scale will tend to accumulate at some hot spots. It decreases heat transfer (ie is insulating) and cuts down on the cooling effectiveness.

In addition, there are the possible chemical reactions of chlorine (common in tap water) and sodium to create chloride salts. Jeff Bertrand (contributor to Motorcycle Consumer News and fellow lister) cautions that, in his experience, this can often result in a highly corrosive soup. Not a pretty picture!

Though this is a normal chemical reaction of chlorine and sodium, I haven't researched this enough to determine to what extent this occurs nor what concentrations are likely to produce negligeable or more significant effects. What I do know is that preventing the formation of this corrosive soup requires a very simple and inexpensive product that is available at every drugstore: distilled water. A four litre jug (approx $2) of distilled water is probably enough to fully flush out a cooling system.

So using distilled water is critical for both flushing and mixing.

Copyright
Bruno Valeri 2003-2008

 




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