I suspected my thermostat for a while as it also took ages to reach 90, although would get up there on a motorway run. However, assuming that something is happening at 90 to stop it from rising above that temperature, and it is probably the thermostat opening, then it must be functioning to some extent, even if it is leaking a little bit at lower temperatures. What speeded up warm-up for me was fixing the booster heater. Now gets noticeably warm in about 2 miles, still takes quite a while to reach 90, and doesn't really ever get there on a day like today just driving around town. Matt