I have a 1984 380SL and I have noticed that the temp. gauge will sometimes rise quickly while idling at a stop light from about the usual 80 degree position to up to about 100 degrees but will quickly sort itself out once I pull away from the light.

Also, after driving for a while the oil gauge will drop to say "2" at idle speed but will immediately return to the usual "4" position when driving again.

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1984 380SL (58,000 miles)
Anthracite on grey
1997 BMW 540i
Alpine Silver on Burgundy