1989 GMC truck 4 cyl 2.5 liter The overheat light comes on after about a minute's driving. I have flushed the system, replaced the hoses, replaced the whole radiator, and the coolant temperature sensor and the thermostat(tried two separate new thermostats). I tried removing the thermostat altogether, and this has been the only thing that worked: the overheat light no longer comes on. The water pump seems to be working fine, although I haven't dismantled it to inspect the impeller. Is there a chance the overheat warning is a false signal due to purely electronic considerations?