Volvo: 1999 Volvo S70, orange arrow, coolant temp

Question
I have a Volvo s70 and I am having problems with my gas mileage. I have not changed locations, I have replaced the spark plugs, and I tried some fuel system cleaner and My gas mileage has gone from 21.6 to 5.2 in about 3 months with the last 2 weeks having the most decline. What could this be, and how can I fix it. I have already replaced the engine in this car about a year ago, so I know how much trouble they can be. I also would like to know why the orange arrow that signals when you are in winter mode, is always flashing. My mechanic who has worked for a Volvo dealership for 13 years says that it might be a faulty switch, but the car also is hard to get going when the speedometer quits working, what could cause this problem?

Answer
Tanya,
The fault codes will need to be read and those faullts taken care of. There is the possibility that there is a fuel leak, or a overpressured fuel system, bad coolant temp sensor. Get the car to a shop that can work on a Volvo and have them do these tests and report the results to you.
The flashing arrow would also indicate a fault code in the trans system. Have those codes read and see what they are, yes they might indicate a faulty switch.