123 temp gauge

hey,

i was wondering what to do about my temperature gauge in my '82 300D. the other night i was driving and it was about -8 (celcius) and my engine temp went up to 100 Celcius(where it usually is) and then started jumping past 100 by about 15 degrees, it would jump up and down at about 5 or 6 degrees at a time , i was worried about over heating but the gauge just seemed to be very innacurate and i was wondering what am i to do here? thx

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Maciej Jamrozek
Born in '82
'82 300D TurboDiesel 500+K