There appears that an explaination of the Fiero cooling system electricals is in order; lets look at the engine first. There are four (4) sensor/switches on the Fiero, 4 cyl or 6. On some of the 4 cyl A/C cars, there's a two speed fan; it has two switches in one shell to activate the fan. These cars are identified by a large white ceramic resistor on the fan frame rail. So when you ask the guy at the parts counter for a coolant sensor, you better know which one! We'll do the two temp sensors first. The others are switches.. Temp sensors are nothing but variable resistors that change resistance with temperature; as the temp goes up, the resistance goes down. One sensor (2 wire) is for the ECM. This is the ONLY coolant sensor the ECM sees. It tells the ECM, obviosly, how hot the motor is so it can go into closed loop and aids in determining proper timing & fuel mix. The other sensor is combined with a switch in one assy. Both this switch and sensor operate the dash lamp and temp gauge respectively.
As for switches, they close at predetermined temperatures and make something happen. The previously mentioned switch in the same shell with the gauge sensor, lights the temp lite on the dash when it closes.
I have found that the connector shell on the V6 gauge/lamp sensor is melted or gone due to the proximity to the exhaust manifold. The wires can be simply slipped on the terminals without the shell. How do you tell which wire and/or terminal is which? Easy. Install either wire on either terminal. Run the car. If the gauge doesn't come off cold, reverse the wires. To check the gauge and lamp, short either wire to ground with the ignition on. The gauge should go full scale, and the lamp will illuminate, respectively.
A stand alone switch is for the fan. It closes at 235f. This switch, along with one built into the A/C controls, completes a relay coil circuit to ground. The relay contacts actually supply the large current needed by the fan. This relay is located in the LH front corner of the front compartment. To check the fan, short the Dk GRN/WHT wire on the fan switch on the engine to ground with the ignition on. The fan should activate. This fan switch is notorious for not operating. If you find your car (this goes for other GM's as well) overheating when not in motion, but cools down at speed, its a good chance this switch is bad. Turning on the A/C automatically activates the fan.
Speaking of A/C, there's another switch on the compressor that turns on the fan when pressure reaches 280#. Why this is there, I don't know, because, as mentioned above, the fan runs anytime A/C is dialed up. The replacement compressors I've been getting lately don't have this switch so I leave the lead off. (they also don't have the clutch switch, but that's another story).
As mentioned, some A/C'd 4 cyl cars had a two speed fan. The switch is in the same postion, but now it contains two switches in one assy. and has two leads. The low speed comes on at 221f and the other closes at 248f.
SENSOR/SWITCH PART NUMBER WIRE LOCATION coolant fan switch dk grn/wht 84-86 two speed 3050223 lt grn/blk L4- LH front of head 84-86 non A/C 3040674 85-88 V6 all 3040674 dk grn/wht V6- RH top of engine near thermostat gauge/lamp sensor dk grn 84-88 all 25036628 L4- LH front of head 85-88 all 25036809 dk grn/wht (V6) tan (L4) V6- LH rear head next to edge of exhaust manifold ECM coolant sensor 84-88 all 10045847 blk & yel L4- thermostat housing 85-88 all 25036979 V6- RH top of engine near thermostat
From: Tin Man
The coolant fan of 87 - 88 4-cyl. Fieros IS controlled by the ECM, and at least according to the Helms manual, its operation is speed dependent.
From: Jukka Alve
Here is the paragraph from the Helms manual on Electric Cooling Fan Control (pg 6E-11 in the 87 manual):
Under certain conditions, the ECM may control the electric cooling fan to cool the engine and A/C condenser. At cruising speed, the ECM may turn the fan off for better fuel economy.
From: Lee Brown
Here's what I do to purge air from the coolant system.
The trick is to take the thermostat out and leave it out until you are sure the _all_ of the air is purged from the system.
Park on level ground.
NOTE: Fiero owners should bleed the coolant system _anytime_ the coolant reservoir runs dry. i.e. system has sucked air into the radiator.
From: Terry Loveless
There is a drain plug at the bottom of the radiator, under the coolant fan, on the passenger side. You won't be able to see it from above, but you should be able to reach it. It is just a thumb-screw plug that you should be able to remove with your fingers. If it is too tight, you might need pliers to loosen it.
There is a drain plug towards the rear of the coolant pipe on each side of the car. They are Torx, I believe they are T25 or T30.
|Temp never rises|
|Temp rises when not moving|
|Fan never comes on|
|Fan always on|
|Overheating, but no leak|