Hot Jaguar/

2000 S-Type V8. 66-K everything runs great and I get 26MPG on trips 17 MPG in town. Two years ago I replaced the factory water pump with a new model with a metal water wheel rather than plastic. Recently the indicator light has sent a false signal of overheated engine on three occassions for about 20 seconds and then returned to normal. The engine was not over heating. Any ideas? I do not want to go to the Jag dealer for $$$$. HELP!