Coolant Problems, Radiator fans wont come on.

I have a very odd problem. My car won’t get hot when I drive 45 MPH or above, but when I get in the city it will start to get hot when I enter stop and go traffic.

So I pulled over and popped the hood. I left the engine on and the fans where not on. I know the engine was hot enough to kick the fans on.

I have a few questions:

1.) Is there a fan switch or something like that that is responsible for triggering the fans?

2.) Could the problem be the engine coolant temperature sensor?

i too have a problem with that. When i drive my car on the highway and i am able to do 45-65mph my cars' temp stays about 180 or 190 but as soon as i am in traffic it begins heating up terribly especially if i have to sit still while in drive at red light, and when i put it in park or neutral the situation only gets worse. I have checked the coolant level and it is fine. I have no leaks, it is full. I have checked the oil, and it isn't doesnt have any milky residue in it. I had a new 180 thermostat put in and a new sending unit for my electric fan, and the fan has been tested and is good, however the fan doesnt seem to kick on untill the temp gauge almost redlines and thats when the water starts to boil. This has just become a problem recently and i have no clue what the problem could be, so i was wondering if anyone else had this problem and found a solution or had a suggestion! thanks

I have a 130K mi 97 GAGT and it runs hot as well. The fan seems to work normally. Had the coolent flushed twice and was told that the radiator may be cloged. I am going to check the thermostat and relay at a second mech. From what I've been learning on this board is that they just run hot and driving habits and styles seem to dictate how they adjust. So a different combination of fixes and adjustments are needed for each car. The radiator cloging is an interesting theory. They do seem a bit on the lightweight side for this car. Let me know what you think.

I would check your fan relay. And you said you replaced the coolant sending unit already? IF you did make sure it is in properly and that the connections are in good shape. Last resort is you could always wire the fan to a switch.

You need a scan tool to monitor the temperature. The computer grounds the fan relay when the tempature hits 220 degrees. If the computer is getting false information, it can turn it on too late as in your case. You need to monitor the coolant tempature to see what it is actually reading. If it reads 220 and your guage is red lining and about to overheat, the sensor might me defective, even though the check engine light isn't on. I've seen this before. My 1998 Grand Am doesn't run hot at all, about 1/4 the way on the guage. On the highway, the natural air blowing into the radiator is enough to keep it cool. In city driving the fan needs to work.

Good luck