Hey Yoni - Your low speed overheating problem sounds like an issue often associated with a failing mechanical fan clutch. The best solution is to replace the fan clutch or alternatively refilling it with the proper type and quantity of silicon fluid. There are several good write-ups on the procedure. Like others have also mentioned, for the best possible cooling performance check your thermostat and add “water wetter” to the radiator.
In addition to correcting the performance of the mechanical fan clutch, you might also want to add a manual toggle switch to the circuit that turns on the electrical cooling fan mounted on the front side of the radiator.
Normally the electric fan is turned on by either the A/C Refrigerant Temperature Switch (mounted on the A/C dryer) or the Radiator Coolant Switch (mounted on front left lower corner of the radiator). Once the temperature for either switch has reached the trigger point, a ground is applied to relay 18 (A/C cooling fan relay) which directs power to the cooling fan motor. By adding a toggle switch ground in parallel with the two temp switches, you can apply power to the electrical cooling fan as soon as you see the temperature gauge begin to climb. This can be especially helpful if you find yourself sitting in heavy traffic.
I typically mount the new toggle switch in the parking brake handle housing on the left side of the drivers seat.
Good Luck, Michael
