95 nissan altima overheating

ok i recently put in a used motor in my sisters 95 nissan altima because her last one warped. For some reason the cooling fans are kicking in way too late. I replaced the coolant temp sensor and thermostat thinking that was the problem but still nothing relays are fine and fuses are fine. Is there anything wrong with the 95 coolant temp sensors? I used a new aftermarket and a new oem but nothing changed.Im thinking ecu but would like some other opinions. Thanks

My first thought was ECU... No way! After looking at the circuit diagram I am not as sure. I still think it is an input problem. I suspect that the ECU has individual components for each fan just like each fan has seperate external wiring and relays. The fan relay wires from the ECU are different colors. Could radiator restriction limit water flow to heat the sensor? I don't think my fans ever come on unless the A/C is on. Even after idling for more than 20 min at over 110 degrees my temp guage stays below 1/2. Maybe the radiator won't cool very well, possibly from block sealer used with the warped engine? I think if her radiator was good, the engine would stay cool without the fans comming on.

Could radiator restriction limit water flow to heat the sensor? I don't think my fans ever come on unless the A/C is on. Maybe the radiator won't cool very well, possibly from block sealer used with the warped engine?
Brand new radiator and the fans do kick inn just when the gauge is already near hot.

Ok, I understand you have a new radiator and that your fans come on when the temp guage is nearly to hot. The question I have is, what is the normal position of an Altima water temp guage when the fans cycle on? I think 4trackmixtape mentioned that his guage reads pretty hot when his fans cycle on. I am saying my Altima does not overheat or run above mid range without my fans ever needing to cycle on. And that it is hotter here than where you are. I am thinking you may have a circulation problem. If the cause is a circulation problem and it were solved and your temp guage stayed below 1/2, the fans would not be an issue. Under what type of circumstances does your temp guage go beyond 1/2? Have you checked three fan relays? Maybe your fans don't come on at Low speed, and kick on Hi speed at the higher temp.

Thanks for your input. I changed the ecu because i got one for cheap and it fixed the problem fans kick in normal now.