I found the following TSB that mentions an erratic water temp gauge.





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Article No.
97-18-9 COOLING SYSTEM - TEMPERATURE GAUGE FLUCTUATION - VEHICLES WITH 4.0L ENGINE
NOISE - "THUMPING" HEARD FROM WATER PUMP AREA - VEHICLES WITH 4.0L ENGINE

Publication Date: SEPTEMBER 2, 1997

LIGHT TRUCK: 1994-97 AEROSTAR, EXPLORER, RANGER


ISSUE:
A "thumping" noise or temperature gauge fluctuation may occur on some vehicles. This may be caused by the water pump delivering an uneven flow throughout the engine.

ACTION:
Replace water pump and gasket with revised Water Pump (F7PZ-8501-AA) and Gasket (FOTZ-8507-A). Refer to the appropriate year Aerostar/Ranger/Explorer Service Manual, Section 03-03, for water pump replacement procedure.


PART NUMBER PART NAME
FOTZ-8507-A Water Pump Gasket
F7PZ-8501-AA Water Pump


OTHER APPLICABLE ARTICLES:
NONE

WARRANTY STATUS:
Eligible Under The Provisions Of Bumper To Bumper Warranty Coverage

OPERATION DESCRIPTION TIME
971809A Replace Water Pump And Gasket - Ranger And Explorer 1.3 Hrs.
971809B Replace Water Pump And Gasket - Aerostar 2.1 Hrs.

DEALER CODING
BASIC PART NO. CONDITION CODE
8501 42

OASIS CODES:
204000, 204200, 402000, 497000, 702100