At the bottom offside of the engine there is a metal block, fed with cooling water which the fuel pipes are also connected. This pre heats the fuel (only necessary in winter, if at all) which prevents wax formation. In summer time it also keeps the fuel at water temperature, should excess temperatures be encountered. You can't adjust this, and indeed there is no need to. The fuel injection pump can easily deal with fuel at these temperatures so there is absolutely no need to worry about it. Its only the modern common rail or pompe deuse engines that have fuel coolers - they may suffer from fuel aeration at extreme temperatures.
John
December 2007
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