I sold my old Volvo on e bay and now have my father in laws '93 Honda Civic. I realised that the thermostat must be knackered as the car took forever for the engine to warm up, the heater didn't work well and the choke didn't seem to come off for the first 6 miles of every trip.
What difference did changing the thermostat make? the miles per gallon has gone up from 25 mpg to 40 mpg, the car runs better and the heater works.
I've never changed a thermostat on a bike before but I always replace them as soon as I buy a car as they're always knackered. Three bolts, ten minutes and job done. I've worked out that it'll save me £640 a year just on the petrol I use driving to work. That's going in my saving for a TDM 850 fund!

Thats great news! Running cold can kill the MPG, as you found out!

You can always test a thermostat, remove it from the vehicle and place it in a pan of water and heat it up it should go from closed to open as the water heats, you can get technical and use a thermometer to monitor the temperature while its happening. Some thermostats have the temperature range stamped on them.



Yours Wilf must have been stuck open or the car would have over heated.

When thermostats fail they usually stay open - in all my years of motoring I've had many fail but never one that stuck closed.

They usually cost less than a tenner so I just change them anyway.

For what they cost to replace, its not worth testing them if you suspect theyre knackered.
When i buy a car i generally replace the cam belt, waterpump and thermostat as a matter of routine,,, you generally dont know if/when its had a cam belt and waterpump, and for the sake of a few quid the thermostats in there as well.
Personally as a mechanic , i never trust the service history 100% anyway. When i replace the one on our car, i could tell it hadnt been on there too long, so it had been changed at some point, but i believe it better to be safe than sorry.