Hey, long time since I've posted, but I've been lurking occasionally.
A few weeks back I was driving a short stretch of freeway when I noticed my temp gauge pegged at the max! I was able to exit in a couple of miles and checked my coolant resevoir and found it empty... boiled over! I filled it with some cool water and made it the rest of the way home.
The next morning I needed even more water and I took it (a bit slowly) to a Mazda dealership for service. They told me my radiator was rusted and leaking near the cap. After they switched that out and ran a test, they saw the temp starting to elevate again.
They kept it for another day. They suspected a gasket leak, but their diagnostic machine showed that was ok. They checked the thermostat again (which had passed some tests on the first day in the shop) and found it to be sticking intermittantly. So now I have a new radiator and a new thermostat.
Looking back, I probably did have at least a small leak. A week earlier I topped up the coolant fluid.
Now, I don't know for sure that my little grille block caused or contributed significantly to needing these repairs, but I have to wonder. The confusing thing is that for all this time, I did not notice a higher coolant temp on my dashboard gauge, and I did not notice the fan coming on much more frequently that it did before (but I do admit that I can't easily hear it except in my garage). But, in any case, I'm not going back to using a grille block on this car. I didn't see much benefit in the milage, and once bitten, I'm twice shy. I hope none of you using a grille block meet the same fate.
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Sohl