In time the contacts on the motor pod that drives the gauge needles can build up oxidation and start to make poor contact. A bad ground or a poor contact can peg a gauge. Usually it is the temp gauge though. Your oil pressure gauge should read high. SHould read atleast at the 3 bar mark when you are driving. Typically no less than 2 bar when idling is ok. Oil pressure pegged is typically not bad.

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Christopher Henkel
1990 190E 2.6 - Arctic white SOLD
1986 190E-16v - Blauswartze
1993 300CE - SOLD
2003 W208 CLK 320 Cabriolet - Magma Red