94 altima intake manifold / overheating

[acuevas123]

Hi All,
I recently replaced the intake manifold gaskets and a water pipe on my 94 Altima. Unfortunately, it ran very erratically and still overheated even though there are no water leaks. I got a diagnostic test and the 'code' pointed to the knock sensor. I bought the sensor and am proceeding to replace it.

My question(s) is/are:
1. I will buy new gaskets - should I use gasket sealer on the gaskets?
2. What could be causing the car to overheat when there are no water leaks?

Thanks.

[QR25DE]

Temp sensor, thermostat if its stuck closed.

[wade001]

or it could be a bad radiator, how long does it take before it over heats?