Radiator Cooling fan issue (Page 1/1)
ninedriver JAN 29, 05:35 PM
88GT
My radiator cooling fan is not turning on. I removed the plug from the sensor near the thermostat housing and with the ignition in the run position, I grounded the terminal in the plug end. I could hear the fan relay cycle each time I grounded the plug, but the fan wouldn’t turn on. I then removed the fan and unplugged the 2 pin connector at the fan motor. I hooked my volt meter up to the 2 pin connector and set to dc volts. My ground lead to the black (ground) wire in the connector and my red lead to the black/red (positive) wire. Again, I grounded the connector that goes to the sensor by the tstat housing. The relay closed and my volt meter read 12.7 volts(battery voltage). With the fan removed from the car, I used two jumper wires and hooked it right up to a car battery and she came right to life, sounded great and didn’t skip a beat. Hmmmm, something ain’t adding up. I plugged the fan back into its harness, grounded the plug by the sensor...relay closes (clicks) but the fan doesn’t run.

Anyone got any thoughts?
skywurz JAN 29, 07:53 PM
Dirty/corroded plug?
eti engineer JAN 29, 08:06 PM
Agree. Check your connectors. Unplug each of them and see if there are any signs of corrosion, burning, etc. Buy some contact cleaner, like CDC Electro-Kleen and spray in each connector. If it's not this, then you need to start tracing your circuit. I have actually had a corroded circuit that read battery voltage until I put the load on it, and then it dropped to 1.2 volts because of a poorly crimped factory ground connection. So when you do your tracing, have the whole circuit hooked up. Under no load, a corroded connection will pass nearly full voltage, when under load, it will act like a voltage-dropping resistor.
theogre JAN 29, 09:32 PM
Do this First....

Rad Fan is Grounded on "inner fender" next to left HL Lift assem.
Big wire of 2 there.

clean/fix both wires and 1 ground to right HL assem same as this.
May need new screw(s) and/or drill new hole(s). Clean to bare metal and use brake grease to stop rust.

Turn on HL, Pull HL Motor connector(s) then turn off HL should get enough clearance to fix the grounds.

Wire(s) can rot/break inside the plastic. Quick test pull wire and watch plastic at crimp end. Plastic stretch is likely wire rot. need to cut back to better wire and splice or find another place to ground it.

2 small wires ground HL motors and all front bulbs but only 1 big wire on left grounds the rad fan.
Likely HL can be brighter after fixing them unless HL or other HL E-parts are "bad."
(See my Cave, Headlights)

------------------
Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave

[This message has been edited by theogre (edited 01-29-2021).]

ninedriver JAN 29, 09:58 PM
Hey guys
Thanks for the input and direction. I’ll check things out tomorrow and report back.
ninedriver JAN 30, 04:17 PM
Update......solved!

I checked all the grounds and connectors/plugs and all checked out good. So, I began voltage drop testing, thanks eti engineer. I’ve always done voltage drop testing on the battery, cables, and starter system. Never thought about voltage drop testing a smaller down line circuit.
As stated earlier, the relay closed and I had 12.7 volts and the radiator fan plug. However, when I plugged in the connector, powered the circuit, and ran a voltage drop test from the battery to the plug end, it had over 12 volts of drop. I further isolated the circuit and ran a voltage drop from the input of the relay to the output wire at the radiator fan. Same 12 volts of drop under load. I pulled out the relay and took it apart. At first glance, it looked great..shiny, no green crusties or anything. I bench tested it and the contact closed and had continuity. Upon a closer look, the contacts that close to complete the circuit were burned/ corroded. After some delicate sanding and cleaning I reassembled the relay, plugged it back in, and it functions perfectly. I love it when a plan comes together. Thanks guys.