Overheating

[henry]

I've got an '80 FI and the gauge doesn't operate when the ignition is turned off.

It should operate in have the way of the ignition switch.

[henry]

That could be because the water in the bottom of the radiator is still hot and as the water pump is not working one the engine has been turn off ceasing water flow the head will be hotter.
You should also have the two temp sender on top of your head. the front one is for the temp reading of the gauge and the rear one is like a switch that switches to the hottest part once it reached a certain temp (I don't know what that is)
I think your gauge may be okay.
If you think it is suspect, try and swap a gauge (check all the earth paths are secure as well)
See if you can compare the sender values with another. Measure both voltage in circuit, then disconnect and measure the resistance. The voltage and resistance should be higher when colder and go lower the hotter the car gets. the rear switch should have high resitance and then go low once it reached its temp setting.
I measured mine recently but think I have the results at work and I have taken the week off (My wife has just had a baby No.2)
See if somebody on this forum has similar results.
It may sound that you may need a bigger fan as stated or get a switch that comes on earlier.
You could try Marks set up http://www.allisonsautomotive.com/products.html scroll down till you get to the adjustable thermostat.
If the ambient air is rather hot, it will be difficult to cool your car down.
Hope this helps

Thank you for the info. I will check that tomorrow.

[henry]

OK. I changed the temp sensors and run two tests:

1) Stat working (Fan on and off):
a) A/C On = Overheated.
b) A/C Off= Overheated.

2) Without Stat. Fan direct(always On):
a) A/C On = Overheated.
b) A/C Off = No overheat.

Next test will be with a bigger aftermarket fan.

[henry]

My car is overheating after I turned off the engine, and the fan is working........... Radiator problem?????

[jimincalif]

Define what you mean by "overheating" when the engine is off. It is normal for the coolant in the engine to get hotter after the engine is off as the block and head are hot and the coolant is no longer circulating. If the temp of the coolant in the radiator is hot enough to trigger the fan, it will run, and this will cool the radiator, but it will not cool the engine when it is not running.

[henry]

OK, finally solved the problem added two new electric radiator fans:

1) Main, 14" working with the radiator stat. Starts at 180.
2) Secondary 10" working with A/C, (separate stat). Starts at 180.

Now, it runs on heavy city traffic with A/C on below 190.

I got home and my son crashed the front of the spider with his car