As John says, get a sniff test done.
If you are (or know someone who is) reasonably mechanical you can buy the kit for about £40 and do it yourself. The kit comes with enough fluid to do dozens of tests.
Be aware there is a risk of scalding if the coolant surges while the filler cap is removed.
Just google "block tester" for more info, local motor factors should stock it.
derv
May 2009
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