I purchase an 86 GT a couple months ago. Overall it is in great shape but the temperature guage doesn't seem to work. At first, I thought the engine was running cool but it should register some temp rise and it doesn't. I have replaced the thermostat. I didn't expect that to solve the problem but it needed to be replaced.
I have ordered the Temp Gauge Sending Unit and the Fan Switch. Am I on the right track? Is there a more certain way to diagnose the problem? As you can tell, I am a novice so any help is appreciated. Also, I am thinking the temperature problem is related to the fan not running. If it begins to sense temperature the fan will kick in? Please confirm.
May I be the first to welcome you to the forum and one of the Fiero's little idiosyncrasies. The gauge sender and the fan switch are two entirely independent circuits. The gauge sender has no effect on anything except the driver's nerves, making him or her wonder if the Fiero is actually running that cool or close to overheating.
Assuming the fan switch operates correctly, it should turn on the cooling fan at about 235 degrees and turn it off, I think at about 210 or 215. The gauge is likely incorrect since a GM wiring snafu causes the gauge to peg at startup. Constant pegging causes the indicator needle to slip on it's shaft. At normal ambient temperatures of 70-90 degrees, the needle should sit roughly on the base of the thermometer symbol and move to the 100 degree mark when the ignition is turned to the ON position without starting the engine.
If the gauge moves to this position, then a test having a 195 standard thermostat would be to start the engine and let it sit and idle until the cooling fan comes on. When the fan kicks on, your gauge should read somewhere around 235. If you have an infrared thermometer, place the dot on the base of the gauge sending unit on the left end of the trunk side head. That will help you determine accuracy of your gauge and sending unit.
If you think the cooling fan needs to be turned on to prevent overheating, you can press the MAX or NORM ac button and it will kick the cooling fan on. It doesn't matter if your AC works, or not. The fan will still come on. It's best to turn it on before it overheats. It's harder to cool it down than to keep it cool.
Usually the temp gauge is dead because the connector baked off and the connector either came off, or the PO swapped the wires for the temp gauge pin and the temp light pin.
If your temperature gauge sender looks different from this one then you have the wrong sender. If the store tries to sell you a sender that looks different than this one then he has no idea what he is talking about. The GAUGE sender on a Fiero WILL look like this one.
This is the temperature gauge sending unit. It has two functions. The wire that connects to the pin that is AWAY from the side notch is for the gauge. The wire that is close to the side notch is for the TEMP light (yes your Fiero has one).
Turn the key on but leave the engine off. Ground one of the wires. Then try the other. One should light the temp light. The other should make the temp gauge (or just pivot in your case) move. Then just make sure the wires are on the correct pins so the two devices work correctly.
---- The Fiero fan won't come on unless you are driving on a hot hot day, or you come off of the highway and are waiting at a light, or you have the A/C turned on. Most fan switches are sold because the owner thinks it should come on more.
Take the wire off of the fan switch on the engine and ground it (key on). If the fan comes on the wiring is good. The switch is also most likely good unless your Fiero has overheated and the fan didn't come on.
[This message has been edited by phonedawgz (edited 07-11-2014).]
Rignt about now, KJENKINS1, you probably wonder what you got yourself into, but the rest of the car is not this bizarre. You just happened to hit a problem. When you get it working properly, you may want to undo the wiring mistake that GM made....
On the two pin combo temperature gauge/temperature light switch each pin works independently. One pin - the temp light switch acts as an open until 235, and then the switch closes to engine ground The other pin has a variable resistance to ground engine ground, and that resistance goes down as the temp goes up. Wired correctly both the light and gauge work(ish)
With the wires swapped the temp gauge is wired to the switch. So the temp gauge will sit at max cold until something like 245 and at that time the temp gauge will swing to max. Since most Fieros operate below that temp the gauge will just sit and do nothing. Having the TEMP light wired to the gauge sender will cause the TEMP light to glow slightly once the engine gets warm. This is also interpreted as non-functional by most users.
[This message has been edited by phonedawgz (edited 07-12-2014).]
Ok, progress. I replaced the sender and the guage works! I was pleased to see it begin to register heat as I let it run. I was not pleased that it get getting warmer and finally to the bottom of the red on the guage, then it back off a little but remained near the red. I shut it off and after it cooled, I pulled out the thermostate (brand new, just put it in). Now it runs and does not get warm.
Is there a way to calibrate the thermostat or is it just a bad one?
Also, I noticed the fan did not come on when it got warm. I had to turn on the AC. Should my next part be the Fan Switch that sets on the block?
See the second paragraph of my first post regarding static positions of the temp gauge needle. If they move to those positions at the proper times then your gauge and sending unit are correct, so replacing the fan switch may be in order.
If the needle sits below the 100 mark when the ignition is turned to ON without starting, then the needle needs to be repositioned. That can be done by removing the instrument pod, pulling the needle off the shaft and setting it back in the proper position. I won't go into that procedure until it's determined that it's needed.