Quote:
Originally Posted by Evil Dan
My car is a bit of anoddity that it is an oval dash 1987S with a single cooling fan, the thermo switch in the radiator is 2 wire but it has the twin fan relay in the fuse box.
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After some thinking...
My guess is that a PO at some point replaced the radiator and fans with the early model single fan and radiator, either because they did not understand the differences, or they could not find a good used late model radiator. They then wired the early two pin thermo switch to the slow speed input on your late model three pin fan relay (probably with some custom wiring), causing the single fan to run only in slow (or high) mode.
This is probably not enough to keep your car from overheating while in standing still or in traffic, as the late model cars need two fans running in either slow or high speed mode (high speed = AC running or coolant temp above 102C). If my theory is correct, right now you have one fan in one speed (high or low) mode only.
Recommend changing the radiator+fan setup to the correct late model dual fan setup, install the correct 3 pin thermo fan switch (likely already installed on the late model radiator if you get one used) and wire up accordingly to your existing (assuming late model) fan relay, as it should have been from the factory. The high/low speed pinout of the late model thermo switch is on Clarks and should give you the basis to connect the correct wiring to the fan relay:
Also, there are multiple different thermo fan switches with different temperature activation points. You must be sure that these are higher temps than what your thermostat is set at or your fans will run all the time. Clarks notes the normal thermo switch (again, late model 3 pin) high low temps are 92C and 102C. If you go with a used radiator this is likely already installed, but you still may want to double check. The temps should be stamped on the brass casing of the thermo fan switch itself.
Can you confirm whether there is custom wiring coming out of the two pin thermo switch on the radiator going to the fan relay (meaning there is no OEM plug, or an OEM plug with wires spliced)? If this is the case then it confirms the PO installed the wrong cooling fan/radiator setup for your car... You will also want to double check the wiring to the fans and see if the wiring for the second fan is clipped or tucked away somewhere.