I've just been speaking to the mechanic who fixed my car.
Apparently there are TWO thermostats!!
He replaced the cheap one I'd put in but also fitted a new OIL COOLER thermostat, that's why it seemed so expensive, but well worth it.
I've done a quick search and found this
http://www.jackthom.freeserve.co.uk/thermostat.pdf
I suggest you replace the oil cooler 'stat first, they cost about £20 apparently.
deke
December 2010