My '86 developed an issue just after replacing the radiator last september, where the main cooling fan would not come on at normal temperature, which in my case was 195, the secondary cooling fan still comes on at 225ish, but it's starting to get bothersome now that it is starting to heat up here in Ga. I went and looked at it today and I jumped the 'B' port on the ALCL, and the cooling fan runs, the cooling fan also runs correctly when the A/C is on. I also tested the relay connections and it's getting 12 v at the terminal 'C' which is a dark blue wire, and it's getting power at terminal 'E' which is a red wire which i'm guessing is a constant power, while there I used a jumper wire to connect the red wire to the dk blue wire and the fan would not turn on. I can't get the connector off at the fan motor, to test for power there. I also tried to ground out the sensor wire on the driver side head and no luck there either. the fuse looks and tested fine in the fuse box. Any idea's on what else to test?

 

Typically the main fan will not come on until 230-235*

 

My car has a modded PROM the turns the main fan on at 195ish and the secondary fan at 225ish

 

Not on a '86 , the aux fan is only controlled by the mech switch in drv side head
Relay for aux fan is on front of radiator shroud , drv side

 

The main fan comes on at 228 F and the aux fan comes on at 238 F. The aux fan is operated by a thermoswitch in the left head. The red wire on the fan relay goes to the battery and the blue wire goes to the relay coil which has 12v on it with the ign sw in run, so the fan won't run if you jump these wires. The grn/wh wire goes to the ECM and is the other relay coil wire and the ECM grounds the grn/wh wire to turn on the relay and thus the fan. Your fan is working as it was designed. What isn't working is your acceptance that below 35 mph, your 86 is going to heat up and the main fan will come on at 228 F and the coolant temp will fall and the fan turns off at 210 F and then repeats. Even 238 F is a nothing for auto engines and will harm NOTHING. Even if you have the fan run continuously, the radiator will not keep the coolant temp at 195 F, the opening temp of the thermostat and your life will go much smoother if you accept the way the cooling system was designed! Also, don't bother putting a lower opening temp thermostat in your 86 because absolutely nothing will change in summer temps, the radiator is not large enough to maintain even 195 F with only the fan pulling air through the radiator. Airflow is much higher when you get underway. As Bugs Bunny says, "Unlax Doc". Your cooling system is working exactly as it was designed to!
Oh, and GM says if your coolant temp gets to 260 F, shut the engine off and let it cool down. You will never see 260!

 

http://members.shaw.ca/corvette86/Co...%20Control.pdf

My 86 with a 170 stat and lowered "fan on/off temp" keeps it in the 170-190, all day long. Sitting in slow/no moving traffic, 185. I have only seen in reach the 200 mark, a few times, and that was after prolonged hard driving.

 

My 86 fan comes on at 225, turns off at 217 WITHOUT A/C.
With A/C the fan comes on at 215, goes off at 200.
I wired the aux fan relay positive to the main fan power wire so that the main fan power energizes the aux fan relay coil, and turns on the aux fan when the main fan comes on.
OTHERWISE,
The aux fan runs whenever the sensor says to. even when driving, which seemed to make it run hotter while driving.
When I disconnected the sensor in the left head, I got about 8 degrees cooler while driving which made me think the fan was actually slowing down or turbulating the air at the condenser and causing a disruption of air flow while driving.
Now, it seems to run at 100 degrees over outside air temp all the time except in the winter where it runs at the thermostat temp on the freeway.
for instance, when it's 100 outside, normal driving, I see 200 unless I'm on the freeway where it's 180......stop and go traffic, it's at 215.
when it's 50 outside, it runs at 175 freeway or city.