Question for the board: I have a 3800SC swap in a '87. I discovered the hard way (stuck in ATL traffic) that the radiator fan wont come on. I replace the fan modual and the fan will come on w/ the AC but not when the engine heats up. Any suggestions? Thanks

You can wire in a switch so you can control the fan without running your A/C all the time.

------------------

ARCHIES JUNK IS FASTER THAN SHAUNNA'S JUNK
12.3 is faster than a 13.2

Welcome to the Forum! Have you given up the cavalry for a 3800? or is that just your PFF name?

The fan switch is separate from the AC. I suspect the sender switch for the fan is failed.

You have one that feeds the ECM and if I recall correctly the AC. The other sender feeds the fan based on water temp alone.

The Fiero Store sells the fan switches which I think GM no longer sells. I had to order the sender for the temperature gauge from them.

I use a DeRale fan unit myself. Hope this helps

Arn

quote Originally posted by Arns85GT: The fan switch is separate from the AC. I suspect the sender switch for the fan is failed. You have one that feeds the ECM and if I recall correctly the AC. The other sender feeds the fan based on water temp alone. The Fiero Store sells the fan switches which I think GM no longer sells. I had to order the sender for the temperature gauge from them. I use a DeRale fan unit myself. Hope this helps Arn

If the the switches that work in the 2.8 also work in the 3.8 then Rodney has them...like 3 different ones (that come on at 3 different temps).

Unless you are using a pre 1991 ECM, it should be controlled by the ECM. What year ECM is the 3800 using? The circuit that would normally go to the fan temperature sending unit/switch would be wired to the fan control output of the ECM. If your coolant sensor is not reading correctly or there is a problem between the relay and ECM would cause that. You should first use a scanner to look at the coolant sensor readings. Most cars with AC would have a low and high speed relays. This of course would be if the ECM has not been tuned to not to control the fan. And the car has been wired to use the older fan temp switch, a coolant sensor, and a sending unit for the gauge. That seems kind of redundant because most 3800 ECMs can do that with just a coolant sensor and sending unit for the gauge.

[This message has been edited by cmechmann (edited 10-28-2013).]

A cheaper and easier way to check ECM temperature is to use an android tablet or phone with an APP called Torque. If I remember correctly you can even get a free version of it. Just configure it with a Blue Tooth OBDII unit for about $20 from Ebay and you can read a lot of different things that might be helpful.

This will only work if you have OBDII. So disregard this is you don't have OBDII.

This way or using a scanner you should be able to determine what the ECM is actually seeing for engine temperature. From there you can probably figure it out. ie. if the ECM temp reading is not right fix that. or if the ECM is seeing the right temp check out pins and wiring from the ECM.

Have fun.

Thanks, everyone, for taking the time to make sugestions. So where is the snsor that checks the coolant temp on a SII 3800SC?

quote Originally posted by Jeb Stuart: Thanks, everyone, for taking the time to make sugestions. So where is the snsor that checks the coolant temp on a SII 3800SC?

Just left Atlanta earlier this year and Atlanta traffic is the truth serum to whether or not your cooling system is up to par. Your fan appears to be fine, with a 3800 SC and matching PCM your cooling fan is/should be computer controlled. The way I would approach this problem is to identify the fan request wire from the PCM and the fan relay control wire. Since the fan comes on with A/C on you don't have to do anything with the fan request wire although this would be the wire to manipulate if you want full control of when the fan turns on.

Once you identify the fan relay control wire from the PCM, use a multimeter to check for its continuity all the way to the fan relay, usually it is the ground for the energizing coil. If that's good check the fan activation temp in the code to make sure it is set at the correct temperature. You also have to make sure you have a coolant temp feed to the PCM although by now you would have a code if you did not. I suspect you don't have the relay control wire connected to the relay which is already confirmed good because the fan comes on with the A/C. It is possible to have a dual pattern activation where the Fiero A/C circuit turns the fan on with use and the PCM turns the fan on at the commanded temp which would explain why your fan works in one situation and not the other.

The proper way would be to have the fan fully controlled by the PCM where the request wire would be tied into the A/C control head circuit so that the PCM turns the fan on when it's needed be it for the A/C or engine temp threshold being reached.