I've been doing a little investigating and found this:
Ford Explorer 4.0 V6 1994 - 1996
Problem: Knocking noises from the cooling system and the coolant temperature gauge fluctuating.
Solution: The cause may be irregular flow of coolant moving through the cooling system. The solution is- Explorer 1994, A new revised water pump and gasket should be fitted. Explorer 1995 - 1996, A by-pass kit should be fitted. The kit consists of a distribution element, reducer element and modified coolant hose.
And this:
FORD:
1995-2000 EXPLORER, RANGER
This TSB article is being republished in its entirety to include 2000 model year vehicles and to provide Service Part(s) and Labor Time information.
ISSUE
A temperature gauge fluctuation and/or a "knocking/thumping" noise may be audible in the passenger compartment on some vehicles. This noise is most pronounced with the engine at normal operating temperature. The noise is caused by steam formation in the cooling system. The noise is then transmitted through the heater hoses and heater core.
ACTION
Install a Coolant By-Pass Kit. This increases coolant flow which reduces steam formation. Refer to the following Diagnostic and Service Procedure for details.
DIAGNOSTIC AND SERVICE PROCEDURE
1. Check for excessive exhaust system restrictions. A restricted exhaust could elevate cooling system temperatures.
2. If dash-mounted cooling temperature gauge fluctuates, check that gauge and sending unit are functioning properly.
3. Check for restrictions or kinks in the radiator or heater hoses.
4. Pressure check cooling system for leaks.
5. Confirm proper Engine Coolant Temperature (ECT) sensor signal to EEC-V processor.
6. Check for correct 50/50 coolant mix. Verify that freezing point is -37°C (+/- 15°C) or -35°F (+/- 5°F).
edit:
7. If concern still exists, install service Coolant By-Pass Kit and verify that concern has been resolved. Refer to the Application Chart in this article.
PART NUMBER PART NAME
F8PZ-8522-AA Coolant By-Pass kit
F8PZ-8522-BA Coolant By-Pass Kit
F8PZ-8522-CA Coolant By-Pass Kit
I have both the gauge problem and an unknown knocking/thumping noise and am now curious if the above things may be my problem.