1999 Nisan altima Fan not working. good at relay. changed temp sensor. will not work when air on. engine gets hot after 15 min. Radiator has been replaced. Fans work when relay crossed.

It should be pulling air into the engine bay. If the fan still doesn't work after being replaced ; check (temp sensor) and fan relay.

you have wasted money on fixing what has not consequence on the oproblem
overheating is from 4 things
1--- no/insufficient water in the cooling system--air lock in system- fill radiator to cap level and bleed air out
2--blocked radiator cores -- have a radiator shop do a flow test
3-- fan not working--no power from relay, ECM. coolant temp sensor , fuses-- have an auto electrician check the circuit
4--- blown head gasket /cracked head-- have a compression test done

If the relay is getting too hot, the most common problem is a faulty radiator fan. The fan motor pulls current thru the relay. The radiator fan motor may be failing after it runs for a period of time.

Maybe your radiator is clogged.

you could have an air lock would bleed heater hoses

Physically look in the radiator under the cap for coolant level, and check the valve in the cap for sticking. If air is present in the radiator it can't get out, and more coolant can't get in,(from the overflow). Either clean the cap or replace it and check that it is the CORRECT cap.
Radiator fins dirty, clean with a strong stream of water, not high pressure water.
Radiator clogged, have it boiled out, or replace.
Thermostat stuck open or shut, replace it.
Water pump worn out, can no longer move enough coolant, replace it.
Fan shroud broken or missing....
Electric Fan(s) not working, Check the fan, relay, fuse and engine temperature sensor's.
Belt driven fan, belt slipping, fan clutch is bad, fan blades have flattened out.

Air dam under front bumper is gone, loose, or broken. It actually has a purpose other than scraping on the driveway or curbs. It forces air up into and thru the condenser and radiator. If it

To start with check the coolant level in radiator...Your vehicle is equipped with a head temp sensor that is designed to shut motor down before it reaches temp. that will result in engine damage..If level is ok then i would look at the water pump at being your next culprit.In either case i would definetly check your temp. sending unit to make sure its operational due to the fact you state that vehicle doesnt get hot...Another thing you can check is to make sure that your cooling fan turns when car gets hot...If fan doesnt come (after you have made sure coolant temp sensor is operational) check fan relay located in power distribution box in engine compartment...

You need to diagnose the problem. The fan is doing what it is being told to do by the computer. You stated the temp gage on the dash is in the HOT position. Either the engine is very hot and the fan needs to run to remove heat even after it is shut off or the gage, coolant sensor or temp sender is defective. Try running it temporarly without a thermostat and see what happens, you may have bought a defective thermostat.

well...it will really help us if you have a temperature gauge because we would not know what is the radiator water temperature.

but anyway...

try these steps...

first check if there is power(12V) to your relay. i mean power that will go to the fan as the relay is energize.

you have 4 pins in the relay. two is for energizing it . and two for the contact that will close once the relay is energized.

jump these pins for the contact, your fan should run. if it did not and there is power, then there is no connection from your relay to your fan.

if it would run, then we can trace the other two pins.

one pin should be directly connected to +12.

test this by using your volt meter.

the the other pin should be connected to your temperature controller that should give negative signal once the engine is hot. the temperature controller should short it out with the engine block which is a source of negative signal.

that should complete the circuit and should energize the relay that would in turn run the fAN,...

i hope you can follow all the tests...

cheers,

drcool

so hard wire a kill switch