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[troverman]

Does your LWB vapor a lot out the tailpipe by any chance? Even when the weather is warm? Start the truck, let it idle for 10 minutes or take on a short drive, then shut off, now GINGERLY remove overflow tank cover. Is there a lot of pressure, enough to blast out coolant? Slowly release pressure. Do you hear a bubbling gurgly sound? Once pressure is fully released, smell the coolant in the tank. Does it smell like gas / exhaust or anything other than coolant? Is your truck suddenly springing coolant leaks all over the place?

My guess is one of two things: if the above is your symptoms, it is either a headgasket, internally cracked block, or shifted cylinder liner. I have heard the LWB's 4.2 engine is particualry notorious for shifted liners. In fact, the local Rover garage said any LWB with original 4.2 with over 100k miles is living on borrowed time. Of course, though many 4.2's have gone much, much longer. My '92 Classic has the same problem: Tons of pressure built up in the cooling system, causing leaks, lots of vaporing, loss of coolant (engine drinks it) and the temp guage never went above the middle as usual. The truck continued (and still does) run fine. What happens is the shifted liner in the aluminum block allows engine compression to escape and blow the headgasket, which than pressurizes the cooling system. This pressure can blow every heater and coolant line in the truck, but the heater core usually blows first. It also can cause some mixing of coolant / oil. Unscrew the PCV valve on the passenger side valve cover (that big metal canister which sticks up on the front) See if the gauze is milky white or foamy (it should be solid oily black) If you're very ambitious take the whole air plenum intake cover off and look inside. There will probably be a milky coating here too. Your dipstick, on the other hand, may not show any of these symptoms, which is good if it doesn't. This is a top-end problem.
So: If it is only the headgasket at fault, change it for $250. If it is a shifted liner, a new headgasket won't last and the only real fix is a new engine. (unfortunantly) Of course, your radiator can get all clogged up too.
Good luck.