Help! Larger (passenger) radiator fan does not appear to work. 91 Civic Wagon, 1.5L

I'm having an overheating problem. The temperature gauge goes very high, almost touching the red zone occasionally, causing loss of coolant through the radiator cap. My 1991 Civic Wagon has two radiator fans. The larger one, on the passenger side, has never come on even when the engine temp is high. The smaller one (driver side) appears to be working ok, off/on when necessary to keep the coolant temp within range.

I have already replaced the thermostat and the radiator. It did not solve the problem.

Question #1: What is the function of the larger (passenger side) radiator fan? Is it supposed to come on when the coolant/engine temperature is high?

Question #2: The fuse box in the engine compartment has a 15A fuse labeled "radiator fan". I know it controls the smaller, driver side fan. Does it also control the larger fan? If not, is there another fuse for the larger fan.

Thank you
Sam

 

Test radiator fan motor by supplying it with power directly from the battery. If it now runs, then the coolant temperature switch may be bad.

 

Thank you Ron. So to supply direct power to the radiator fan, I bypass the "radiator fan relay"? Correct?

Thanks,
Sam

 

Both fans should always cycle on and off at the same time. Whenever one fan is running the other one should be also. The smaller fan on the left side is added for additional cooling of the condenser (A/C cooler in front of the radiator) when the A/C system is installed. Cars without A/C only have a single radiator fan -- the larger one on the right side.

Since the condenser fan is cycling like it should, the switch is OK. The first check is to see if 12 volts is reaching the fan motor when it should be on. Or do the test Ron suggested: unplug the motor and jump power directly to it from the battery. If the motor doesn't run when it has voltage, the motor is bad.

 

As usual, mk is correct. The coolant temperature switch controls both the radiator and A/C condenser fans, proving that the coolant temperature switch is fine. Therefore, test for problems in this order (see diagram below):

1) Blown fuse 15 under the dash
2) Bad radiator fan motor
3) Bad radiator fan relay
4) Bad wire in radiator fan circuit

 

Thank you mk and Ron. I will check them out as you suggested. Your help is appreciated.

Sam

 

Just googled same problem and found this topic. My issue is the fan won't kick and it starts to over heat when idling to long. fan relay from what I have read and pictures I have seen should be on the passenger inner fender wall near the front. However it is not there. Are there any other locations where the relay is located??