Nissan Repair: 98 maxima overheating at idle, gas mileage, air circulation

Question
I would like to know what to check for to determine what is causing my 98 maxima 5-sp's temp to rise after idling or driving in stop and go traffic. This doesn't occur all the time and I noticed that after cutting the engine off, the fan is not coming on. This happens whether the heat or A/C has been on. I have been told that if it was the thermostat, it would be happening at all speeds all the time. The car has about 143k miles and I had a 60k mile maintenance service about a year ago. I had not had any major problems ever as the only owner. Also, I've taken it back to my repair shop since the service to check on why my car's gas mileage is less than before the service, but they find nothing wrong. Alignment is fine and the tires are well maintained and have bought new tires since as well, but no improvement. Thanks for any advice.

Answer
Hi Zeke -

OK, first of all I know you mentioned that the cooling fan is not activating, even when the A/C is on? I am assuming that you have 2 fans attached to the radiator. One of them is supposed to be for the A/C and the other goes on when the engine reaches a certain temperature.

If they are both not working, then I would check to see if your fan motors are burnt. This is a common problem. You will need a 12V test lamp. Run the car until it becomes hot and A/C is on. Remove the wires going to the fan one by one. Check each lead to see whether you have power from it. One of them should illuminate the lamp. Please be careful not to get burned! If you have power, then replace the fan motor(s).

If you do not have power, you must check the fan switch, fan relay, and thermostat.

Checking thermostat:
Because the fan runs on temp, it waits til the thermostat is open before turning on. If the thermostat is stuck, then it will never sense the heat, and your car will overheat at low RPM, but run cooler on the freeway because you have all that air circulation when traveling fast. When you have the car running for a while again, feel the top radiator hose as compared to the lower radiator hose. If one is cool, and the other hot, your thermostat is defective.

Checking the fan switch -
Locate the fan switch, which should be attached to the radiator, and have 2 wires going to it. Again, run the engine til hot, and pull the wires going to the switch. Check it with the test lamp. One of the wires should light the lamp. Then short the wires together and see if the fan(s) activate. If it does, replace the switch.

Checking the relay -
When doing the above procedure and the lamp does not light, you must check the relay, which should be located in the engine compartment with all the large fuses and other relays. 2 terminals should have power. If they do, change the relay.

It is rarely the latter 2, though, so you should find it before getting to that step. From what you describe, I think both your fan motors burned out. Your A/C one probably burned out earlier, and you did not notice, and when the radiator fan went, that is when the car overheated.

Hope this helps!!
calvin