95 toyota corolla 1.8 engine, cooling fan works but only when you disconnect the fan switch, or by pass the fan relay, it's not overheating, but it's causing the coolant to overflow the resivor. Replaced the fan switch, no luck, what can I do to fix this?

Disconnecting the thermal switch or temp sensor puts the engine computer in limp mode and the computer will activate the fan relay to prevent overheating.
The temp sensor could be faulty, or something is not telling the computer the engine is hot enough to need the fan.

For many of the 90's and 2000's Toyota various models - Camry, Tacoma, 4 Runners, Corolla, and some other models it is usually caused by temperature sensitive fan switch on the radiator not operating. Electric fan on the radiator should operate when temp above 200 degrees. Less often the control relay 90987-03003 is defective. Check if bubbling in the radiator smells like exhaust. That would indicate a blown head gasket. A jumper wire from your marker light positive to the lower contact in the fan control relay socket will operate your fan when parking lights are on. The larger vehicles with more powerful radiator fans will need a hefty jumper from a headlight positive to avoid overheating the lighting wiring.

Probably the temperature sending unit...if not that the relays...they should be relatively cheap and easy to replace...

temperature switch. The temperature switch finishes the circuit for the cooling fan. Once the engine reaches the specified optimal temp. the switch completes the circuit and turns the cooling fan on. Hope this helps

For many of the 90's and 2000's Toyota various models - Camry, Tacoma, 4 Runners, Corolla, and some other models overheating is usually caused by temperature sensitive fan switch on the radiator not operating. Electric fan on the radiator should operate when temp above 200 degrees. Less often the control relay 90987-03003 is defective. Check if bubbling in the radiator smells like exhaust. That would indicate a blown head gasket. A jumper wire from your marker light positive to the lower contact in the fan control relay socket will operate your fan when parking lights are on. The larger vehicles with more powerful radiator fans will need a hefty jumper from a headlight positive to avoid overheating the lighting wiring. Make sure the engine is off and warmed up to check the radiator core with your hand to see if it is getting circulation. If it is all cold the thermostat might be stuck.

I'm sorry but I don't have a wiring diagram for that model. However, the corolla diagram may be similar. It shows that both the ac fan relay and the engine radiator fan relay are controlled by grounding through the "water temp switch". In other words, neither fan will work until the engine is warm and the water temp switch is closed. Check out the water temp switch to see if it is stuck open (or stuck in the cold mode.)

Fan switch should be located in the upper radiator tank. Two wires to it. it works off the temp of the water.

For many of the 90's and 2000's Toyota various models - Camry, Tacoma, 4 Runners, Corolla, and some other models overheating is usually caused by temperature sensitive fan switch on the radiator not operating. Electric fan on the radiator should operate when temp above 200 degrees. Less often the control relay 90987-03003 is defective. Check if bubbling in the radiator smells like exhaust. That would indicate a blown head gasket. A jumper wire from your marker light positive to the lower contact in the fan control relay socket will operate your fan when parking lights are on. The larger vehicles with more powerful radiator fans will need a hefty jumper from a headlight positive to avoid overheating the lighting wiring. Make sure the engine is off and warmed up to check the radiator core with your hand to see if it is getting circulation. If it is all cold the thermostat might be stuck.

Then take it to the dealer since it is under warantee. EVAP codes are serious enviormental. Manufactors normally dont want those getting out.

Hi.
A number of possibilities...
1/ lack of coolant in system,
2/ coolant supply to interior heater blocked / controls jammed,
3/ failing thermostat switch to engine fan
4/ failing water pump

#2 may be separate problem and I would check out #3 - after #1, of course!
Hope this helps - if not hold the rating and add a comment below. Cheers, D.