You need to pull the overflow tank probe ,that resides in the radiator overflow tank... and clean the end of it real good (tip)just disconnect the wire harness that connects to the overflow cap ..I used Castrol Super Clean ..I've had to do it twice now in 10 yrs.even though it only has 23,000 mi. good luck it's easy
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1991 5.0 NotchBack,Black
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