Heating) My car has binary heater valve syndrome: full-on or full-off. With the winter we're having so far I don't mind the extra heat. I assume this means a new valve, so which is better? The OEM-style metal unit or the Scantech one? Would prefer the simplest installation over saving $.

Cooling) Car starts and warms up fine, and the gauge goes to at most 8pm position, never higher. It will then drop slowly at highway speeds to nearly the white line at the bottom of the scale. Once off the highway it might stay there or might not and seems to fluctuate.

Eventually the heater cools off at highway speed if I don't fiddle with the temp lever to get some more heat (I know I said it's either on or off but this happens on longer highway trips). Is there some type of thermostat in the heater valve that might be doing this, or is this a sign of the main thermostat sticking open once operating temo is reached?

Apparently it is closing OK when the engine is cold otherwise it wouldn't warm up much at all I would think.

Oh and totally unrelated: how do I tell if my car is LH 2.4 or 3.1? My Haynes book says both were used in 1991.