I have a 94 nissan altima that overheats. I

Faulty thermostat is the most likely one.
Failed Radiator Fan / Sensor (equally likely)
Low coolant level (in radiator as opposed to reservoir)

Faulty water pump. (less likely)

Clogged radiator. (less likely)

Very weak mixture. (even less likely)

While there are a variety of reasons your Nissan Altima is overheating, the most common 3 are a coolant leak (water pump, radiator, hose etc.), the radiator fan, or a failed thermostat.

Nissan Altima Overheating - RepairPal

https://shop.advanceautoparts.com/find/nissan-altima-radiator-hose-lower
https://repairpal.com/estimator/nissan/altima/radiator-hose-replacement-cost
https://www.partsgeek.com/mmparts/radiator_hose/nissan/altima.html
https://www.yourmechanic.com/estimates/nissan/altima/radiator-hose-replacement
https://www.autozone.com/cooling-heating-and-climate-control/radiator/nissandatsun/altima

Does your vehicle take too long to reach operating temperature or overheat? These are about the only reasons for changing a thermostat.

Changing a thermostat is easy. The thermostat sits under the elbow that the top radiator hose is attached to on the engine side. There are probably two bolts holding the elbow in place and it should not be necessary to remove any pipes. Be sure that the new thermostat is properly located in the recess in casting, that the old gasketing has been thoroughly cleaned off and that the new gasket is properly aligned and has a thin smear of gasket cement on both sides before tightening the bolts again. All this should be carried out on a cold engine and some coolant will be lost, which will need to be replaced and checked after the engine has been run and cooled again.

1.6L Engine




1.8L Engine




2.0L Engine




2.5L Engine




3.5L Engine




Hope helps (remember rated this).

1. Improper water circulation: Sometimes, eventhough you are sure that you have enough water on your radiator, your car still overheats. It might probably be that the water is cannot circulate properly, which results to improper cooling process. There are several reasons for this which you can discover by yourself. To verify if the water circulates properly, start your engine without the radiator cap. If water circulation is good, you should notice that the water pops smoothly over the top but still retains the amount. Another way to check, detach one of the ends of your radiator hose from your radiator and see if water flows continously over.
If water doesn’t circulates well, check the thermostat if it’s open. It should be open, meaning clean, and the water can pass through it.
If thermostat is clean and still the water doesn’t circulate properly, then you have to check the water pump. That’s probably where the problem is. A little leak on the pump will cause improper flow of water through the radiator system.
If you are sure that the problem is not about water circulation, another thing you can consider is check the engine oil. Very low amount of oil can cause greater friction of the mechanical system of your engine. If it’s not time to change oil yet, you can add over some amount of oil until advisable amount is reached.
While we can’t be always sure about our engine, especially if it’s not new, we should be prepared when it happens. Bringing extra gallon of water in your trunk will surely help.

Which engine ? Put a drain pan under top radiator hose. There should be a cast part attached. Remove, you will see thermostat, pull install new, clean old gasket off, install new gasket with ORANGE HIGH TEMP PERMATEX SILICONE, re-assemble

Follow the hose that goes from the top of the radiator to the top of the engine. The hose is black flexible, roughly 1.5" in diameter. This hose goes into a "gooseneck" on the top of the engine, secured with a clamp. Remove the clamp and the hose, and remove the gooseneck from the engine. The thermostat will be located underneath the gooseneck. Simply lift out the old thermostat, install the new one, and replace the gasket. Reassemble.

thermostat should be at the end of the top radiator hose on the engine side.drain radiator most of the way to prevent coolant gushing out when you remove hose.unbolt housing replace thermostat.hope this helps

Replace your radiator.

There is one thermostat for coolant and it is located at the end of top radiator hose inside the kneck that it connects to. To replace this the hose has to be removed and then the kneck,thermostat is brass colored valve that covers center of hole,clean old gasket from block side and kneck replace with new one and gasket with a bit of rtv sealant tighten kneck evenly when putting it back on,connect hose wait a short while for rtv to set up and should be good to go,"make sure engine is full of coolant b4 reassembling,just pour strait in engine if it isn't or you can damage new thermostat.overheating can also be sign of water pump not working as well so if still having problem then it is possible cause and on older models radiators get clogged.