red-ryder

2006 4.2 w/ 166k miles. using 1/2 gallons of water---not antifreeze--- every 250 road miles. no visible leaks from engine, no steam from exhaust pipe, absolutely no foam/ mucus in the oil. bought in fla, drove 1360 miles home, ran beautifully, used no oil, got 17--19 MPG. replaced the lower and upper intake gaskets, compression cheked at 150#/ all cylinders. sparkplugs were clean, no indications of an 'offending cylinder'. found lower intake runners 'lined' w/ tar-like sludge. tar was also in the plastic upper manifold, but i chose to clean the lower manifold. used K-1 kerosene and a degreaser brush til both runners and butterfly valves were clean.
my question----what was the source of the sludge? the plastic upper, and aluminum lower manifolds are above the fuel path. is the tar-like gum-pucky an indication of excess engine fumes condensing in the intake runners as air is drawn into the combustion chamber? i understand this is a direct injection fuel system, fuel is never in the intake manifold.

can anyone help me with an explanation, please?

thanx red

Tote-M-Pole

Red,
As far as loosing coolant, check

Hoses
Radiator
Coolant Reservior
Heater core
Freeze Plugs

I have had issues with the reservior before. They develop hair line cracks and only weep, and in your case the H2O would just evaporate and not leave any teltale signs.

Regarding the tar-like sludge,
Is it down stream of the PCV valve?

Hopefully you have found something usefull in this post.
Good luck