Hi,

I have a 1998 Mazda 626 2.0L 4 cylinder with 260,000mi. I just did a bunch of work involving new timing belt, water pump, belts, coolant sensor & coolant sending unit sensor, thermostat, all new coolant hoses (all of them). I finished and started engine and i notice the coolant fan will not turn on when it is suppose to. I have checked the coolant fan relay which is unmarked on mazdas (thank mazda) it clicks when sending voltage to it and i have switched with other known relays that are the same. I have 4-5 volts reading on the coolant sensor plug terminal and there is continuity between relay and coolant sensor plug. the coolant fan motor works when power is supplied so motor is fine. When the car is running, and i remove the coolant sensor plug, Both the A/c fan and the coolant fan come on together, then when i put the plug back onto the coolant sensor they both turn off and neither will come on on their own. also I believe the a/c doesn't work either unless the plug is off of the coolant sensor. I have done my best to "burp" the system for coolant using the funnel on the radiator cap method to get fluid higher up than the engine. heater controls on high,fan low speed, rev engine a little. I feel and can squish coolant fluid in the return rubber coolant pipe so and it gets hot so i feel like coolant is flowing through and the thermostat is opening? i am at a loss of things to try. i don't have and OBD code reader and maybe that is what i need? I thought it is something easy i am just missing. the old sensor worked fine before all the work done to it, also tried the old sensor but still same problem. like it is not communicating with the computer somehow and registering that the engine is hot and needs to come on. i also tested resistance on the coolant temp sensor and resistance drops as the temp heats up. I watched a bunch of Scotty's videos as well as others and i can't figure it out. any help? thanks. I just really like to know stuff and this one has got me beat.