I am trying to figure out why my rad fan doesn't come on when the temperature rises.

The fan works if I turn my air conditioning on. The temperature on gauge comes down right away.

But I want to make sure the gauge is working.

Barring that, what else should I look at changing out? also is there an order to checking/changing things to ensure I get the correct culprit?

1985 2.8 w/airconditioning. No modifications to engine.

Thanks

your fan switch probably isnt working, its located near the thermostat.


thats what it looks like

as for recalibrating. there is no recalibration, its based on resistance of the coolant temp sensor located on the rear bank head near the #6 cyl. there will be 2 green wires one is for the temp gauge and one is for the idiot light.

well lol i should say there isnt a recalibration but there is..... if your temp gauge is off with a good sensor and youve tested the gauge with the right resistors then you can pop off the needle and put it in the posistion. thats about as close to recalibrating as you can get.

heres a great article that you can look at to get more help form. it also covers the temp gauge needle peg problem as well.

http://www.fierosails.com/tempgage.html

[This message has been edited by Niterrorz (edited 11-10-2012).]

The fan, normally comes on at 220 degrees or slightly above.

quote Originally posted by James Bond 007: The fan, normally comes on at 220 degrees or slightly above.

I believe the fan doesn't normally switch on until the coolant temperature hits 235 F.

Once you determine that the fan is not turning on at the correct temp. You can simply test the circuit by unplugging the fan switch and grounding the wire. The fan should turn on (if the ignition is on too).

If you need to replace that switch, make sure you get an AC Delco unit. I bought a "Standard" brand switch that didn't work right out of the box and replaced that one with a "Napa" brand switch that turned the fan on 240 degrees (too hot in my opinion).

I got a Delco switch sold directly from Amazon. Fan turns on now right about 230 degrees as seen on the engine scanner, 220 showing on the gauge.

To answer the original question in case anyone is wondering, you can calibrate or check the gauge. Go here and scroll to "Zeroing the gauge": http://www.fierosails.com/tempgage.html

Calibrating it is possible with some circuity to map the sensor temps to the specific position of the needle on the gauge but that is a waste of effort. Look at what GM went through to get the newer gas gauges to read even remotely correct. There is nothing you can do with just the sender and gauge other than make it read correctly at one single spot.

On several cars I decided I wanted to make it at least read correctly at mid-scale. I used a scanner and then added in resistance to the gauge line to make it read correctly. In all cases I needed to add between 10 and 30 ohms. Seems small but it didn't take much up at 210-220F. Used a pot to dial in the right amount and then add a resistor of that value. Removing resistance would be more difficult.

But you will never get the gauge to read right across the scale. The CTS and gauge just aren't scaled that close.

[This message has been edited by TK (edited 06-03-2013).]