Hello everyone,

I recently bought a '90 245 DL (w/ M47 tranny) that has ~168k miles. After a month or so of driving it, I noticed something strange about the temp gauge: it offers weird readings. For instance, if I turn the A/C on and drive, the temp needle will hover around the middle of the gauge - just like it should. If I sit and idle for 10 mins or so with the A/C on (waiting for someone), the temp will spike - uh-oh. Driving for under a minute causes a drastic drop in temp reading...back to mid-gauge almost immediately. (Almost as if the thermostat dropped its newspaper, realized it wasn't doing its job and decided to open suddenly, hoping no one would notice.)
However: If I drive with the A/C off, the needle barely gets above quarter-gauge level. I drove home today (temp in the 90's, moderate stop-n-go traffic, no long stretches of open road) with no A/C and it only hit quarter-gauge.
My question is - what gives? Is my car really that cold-natured? Is my gauge screwey? Am I in imminent danger of radiator failure? I'm pretty sure the radiator is original, but the water pump and fan clutch are new (not sure about thermostat). PO took VERY GOOD care of the car - took it to the dealer for everything, so I can't imagine something was wrong and he neglected to fix it.

Thanks for all your help,
Matthew