I have a 95 Nissan 240 and first had a bad water pump so I had it replaced and no more leaks, but it's still overheating. Could it be the thermostat?

 

could be any number of things.

A major problem i had, even after i replaced the whole friggen radiator unit, water pump, and thermostat.... it still overheated. Finally one day it decided to go insane, vomited radiator fluid all over the parking lot of my workplace and blew steam high as your eyes could see...

Took it to the shop and turns out all my steel routing lines or whatever they're called towards the bottom of the engine and radiator were completely ripped up and torn. Also the pressure cap ontop of my radiator was very bad. After about 600 bucks worth of new rubber and steel lines and a cap, it worked perfect up until one trip up to zephyrhills to build a new trunk floor with notladstyle my main big hose up at the top ripped out the side spraying fluid ontop of my engine. After i replaced that for a measly 20 bucks, we checked the line from the resovoir tank over to the radiator, that thing was ripped too. Snipped the end off and pulled it closer and there. My whole cooling system is basically new.


So the moral of the story is dont waste your time trying to find the problem and fixing it one by one, just replace the whole damn thing

 

How long did you drive around with the bad waterpump?

A few reasons why it might be over heating -
1. System not bleed correctly.
2. Popped a HG while the waterpump went to shit.
3. Clutch for the clutch fan is bad.
4. Stock fans not working.

If you caught the waterpump before over heating the motor, then it's most likely air bubbles in the cooling system.

 

I drove around with the bad water pump for about a week, just adding water everytime it goes low until it stalled and died with black smoke coming from the muffler. Also, there's no steam at anywhere around the radiator.

 

maintenance is important