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There are two likely sources for the problem.
First, a blockage in the internal passages of the cooling system - intake manifold, cylinder, head or exhaust manifold.
Second, lack of lubrication to the front cylinder due to a clogged or leaking oil line.
The second is less likely but is the easiest to inspect since the oil line is external. The first is most likely but requires disassembly of the engine to inspect.
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