My heat exchanger gets warm, but mine is a bowman that combined with the
exhaust manifold. some 4108's have the heat exchange combined with the ex manifold and some are separate units.
IMO if the heat exchanger is not heating the water, and he's talking about white smoke. could be indicative of an overheat situation which would lead me down the road of no water flow. impeller on the
water pump is an easy check, as is the on board strainer. and to some extent with out going swimming, you could remove the hose from the engine seacock and use a tool to knock off any sea life living inside the
thru hull. yeah it means opening the seacock and making a mess. but it beats swimming.
in conjunction with above I'd pull the ends caps off the heat exchanger and check the tubes for blockages and replace the
coolant. and for good measure the t-stat.
all in under $100 and a few hours of
work, depending on how difficult access is.
The 4108 does not have a glow
plug. its what they call a thermo start. basically a diesel fueled flame in the intake to warm up the air.
if that solenoid is not working then you wont get a fuel drip to light and warm the intake.