Seems my fan isn't working on my new 88 coupe 4 cylinder. I looked for the switch on the head and couldn't find it. Also where is the relay at . Thanks Rick

I believe with the '87 and '88 dukes that the ECM controls the rad fan.

So which sensor, ecm temp or gauge temp or does one do it all ? Think I saw 2 sensors by the water outlet. I'm use to my 85 so 88 is a little different. Thanks

All I know is that there's no fan "switch" on '87-'88 dukes like there is on all the other Fiero engines. I wouldn't be surprised if this is all covered in the Ogre's Cave.

The ECM gets temp readings from the Coolant Temp Sensor. Could be it is bad.

[This message has been edited by Gall757 (edited 07-29-2019).]

Just so we're all clear, that image above is not an '87-'88 duke.

quote Originally posted by Patrick: Just so we're all clear, that image above is not an '87-'88 duke.

Did the remaining sensors change location in '87 & '88?

quote Originally posted by Gall757: Did the remaining sensors change location in '87 & '88?

Off hand, I don't know. I do know that the '87-'88 duke got a MAT sensor. I just didn't want the OP to think from the diagram that his '88 had a Coolant Fan Switch.

Like Patrick said, the '87-88 Duke doesn't have a fan switch. The ECM acts as the fan switch. It uses input from the coolant temperature sensor to determine if the fan needs to be on. The coolant temp sensor should be on the thermostat housing.

The coolant temperature sensor is just a variable resistor. As the sensor ages, the resistor will degrade. And as a result, the activation temperature of the cooling fan will be skewed. You can check the accuracy of the sensor with an Ohm meter and a thermostat. Measure the resistance of the sensor (across the 2 terminals), and compare it to the actual temperature, using the chart below. If the resistance is significantly different from what's specified on the chart, you should replace the sensor. Because that sensor also affects fueling. AND it helps the ECM determine if it should be in open or closed loop mode.



That said, if your radiator fan isn't coming on at all, it's probably a bad relay. Because if the coolant temperature sensor is completely dead, it'll throw a trouble code. Also, turning on the A/C should turn on the fan (the A/C bypasses the temperature sensor). If the fan doesn't turn on with the A/C, then the sensor isn't your problem. BTW, the fan relay is up front, below the driver side headlamp assembly.

[This message has been edited by Blacktree (edited 07-31-2019).]

I have this exact same issue on my 88 4-cylinder, and found a weird little solution.

When I turned on the AC (hot or cold, does not seem to matter), the front radiator fan kicked into gear.

Just something to maybe try, hope this helps.

EDIT: Wow, totally missed what Blacktree said, yup, follow that exactly.

[This message has been edited by Vicophine (edited 08-01-2019).]

Thanks Blacktree. Finally got around to working on my 88. I did notice that the fan comes on with the a/c. I believe I'll change both the relay and Temp sensor.

quote Originally posted by Lilchief: Thanks Blacktree. Finally got around to working on my 88. I did notice that the fan comes on with the a/c. I believe I'll change both the relay and Temp sensor.

Just FYI, if the fan comes on with the A/C, the relay is OK.

Has your engine shown any signs of actually overheating? Are you positive the engine is getting hot enough for the ECU to be turning the fan on? Keep in mind the fan doesn't get activated by the ECU until the coolant reaches 235°F.

quote Originally posted by Patrick: Keep in mind the fan doesn't get activated by the ECU until the coolant reaches 235°F.

That's assuming the temperature sensor is working correctly. The reason I suggested the multimeter test is because that activation temperature can be affected by a degraded sensor. Unfortunately, the ECM doesn't set a trouble code unless the sensor has a dead short, or an open circuit. So the reading could be WAY off, and it won't set a trouble code.

quote Originally posted by Blacktree: That's assuming the temperature sensor is working correctly. The reason I suggested the multimeter test is because that activation temperature can be affected by a degraded sensor.

Oh, I completely agree. My point was more to address the fact that it's very common for people to post here who are concerned that their fans aren't automatically coming on, and it turns out that their coolant simply hasn't actually reached (the factory setting) of 235°F yet.

Yep, we're both in agreement. I just wanted to make sure all angles were covered.

Well I changed out the relay, guess I didn't need to. Oh well. Tomorrow I'll change the temp sensor. The gauge goes to 240 before I turn on the a/c. Also my 88 coupe has a 120 speedo the different tach, compared to my 85 gt and 2 gauges on the center dash. Would that have an affect on it ?

quote Originally posted by Lilchief: The gauge goes to 240...

Which doesn't necessarily mean a thing... unless you've actually calibrated the temp gauge/sender and know that they're both accurate.

Went and got an infared temp gun today. Guess the gauge is off by about 40 degrees. The temp gun read about 225 at the base of the thermostat housing, the gauge read 260. That's when the fan kick on and got it down to 195-200, the gauge was at 240. So now I need to find a sending unit for the gauge. Where would be a good place to get one? Think there's something odd on one of the corners. Thought I'd give everyone an update. Thanks Rick

The temperature gauge sender is an inexpensive and widely available part. For example, I checked RockAuto and they have over a dozen brands available. Most of them are under $20, some under $10.

Well I got both sensors changed today. But upon taking the cap off found no thermostat. Guess there's no way to put a stat between the housing and head is there ? I tried to find a picture of the housing but had no luck. Looks like a small 1/2-5/8" tube in the center. I put a small rubber hose in it and seemed to go all the way into the head. Hope there's no stat in there. Got a new stat and cap on order. Sorry I'm still learning on these 4 cylinders.

[This message has been edited by Lilchief (edited 08-07-2019).]

The Duke and V6 use the same thermostat. Just FYI.