Jaguar Repair: Thermostat, coolant temperature sensor, jaguar vanden plas

Question
QUESTION: Hi there,
Another question for you, I went to a Jag dealership and they did an estimate on a fuel problem I had, they found out that the coolant temperature sensor was faulty and that the thermostat was stuck open.  Would those two things cause it to run really rich and die repeatedly?  Not that I don't trust them, I'd just like your opinion...

Also, they said that it required two thermostats, is this true?  If so how do I know the difference between the two and where are they located?  

One more thing, the dashboard lights don't work, what could be causing this, already checked fuses...

Thanks again in advance for your expertise!

Blake

ANSWER: Hi Blake,
You didn't tell me what kind of Jaguar you had and what year model. I have no way to guess at what kind of car and what year you have.
Howard

---------- FOLLOW-UP ----------

QUESTION: Ha, yes you do need that information, its a 1985 Jaguar Vanden Plas, sorry I didn't include that information in the first place.

Blake

Answer
The 85 Jaguar Vanden Plas is a XJ-6 with a trim package and it only has one thermostat. Only the 12 cylinder cars had two thermostats. The coolant temp sensor for the injection system can definitely cause the engine to run rich. It is a major controller of mixture. A bad thermostat has little to do with a rich mixture. If the thermostat were stuck open it would take longer to warm up and that would keep the coolant temp sensor in a rich mode longer. However a colder engine needs a richer mixture so it would not effect it very much, only a bad coolant sensor would make it stay too rich.
Howard