Check to make sure the fan is running. Turn on the A/C, the fan should run continuously with the A/C on. If it runs then check the thermal switch for the fan, if not the fan is bad. Make sure there is no air trapped in the system, by bleeding the cooling system.
The thermostat on a 96 Nissan Altima is located on top of the engine at the upper radiator hose. It is contained under the thermostat housing which holds it in place.
the thermostat is located at the engine end of the lower radiator hose inside of the housing that the radiator hose connects to.
Ingeneral, the fan will run only if the temperature of the radiator is above the normal range. If the fan is running, then the radiator must be over temp unless the radiator fan thermostat or it's relay is defective. If the radiator truly is over temp then you have a larger over-heating problem You state the thermostat was replaced. if you replaced the fan thermostat then either the radiator really is over temp and it is doing what it should, or there is a problem with the thermostat-fan relay or switch. If you replaced the engine thermostat that controls the flow of coolent between the engine and the radiator, then that probably wasn't your problem and you should look elsewhere for an overheating cause. I would start by determining if the engine actually is overheating or not. If it is, I would look for coolent system problems like the engine thermostat (if you didn't replace it already), water pump, leaks, scale build up in the radiator, or blockages in the system. If the engine isn't overheating then I would consentrate on the fan, fan thermostat and relays.
water leak or bad thermostat
There are numerous reasons why a Nissan Altima will overheat. One such reason is a closed thermostat or the radiator may be leaking.
The 2003 Nissan thermostat is located inside of the thermostat housing. You can follow the bottom radiator hose directly to the thermostat housing.
could be your thermostat is stuck or perhaps and needs to be replaced.
The 1997 Nissan Ultima thermostat is located on the front of the engine. You can follow the water supply hose from the radiator to the thermostat housing.
The 2005 Nissan Ultima water temperature thermostat can be found on the front of the engine. You can follow the water supply hose from the radiator to the thermostat housing.
thermostat location on 2003 Nissan altima
You will need at least $300 to replace a radiator in Nissan Altima.
Take off the thermostat housing which is located right where the top radiator hose clamps to the motor. thermostat will come right out. be sure to install the new one in the same way you take the old one out.