Should be a drain plug either at bottom or rear of radiator or remove lower hose
No. One fan is for the radiator, and the other is for the condenser. If you have the A/C on, they should both be on. Else, just the one for the radiator, if the thermostat is open.
when should the timing belt be changed on a 2007 Nissan sentra
If your security sensor in your 2001 Nissan Sentra 2.0 is jarred or jammed you should have it replaced.
The 2003 Sentra has a chain not a belt and should in fact last you a lifetime.
The Nissan Sentra should not have any other heater installed due to fire hazards. The stock one is very good.
Cylinders compression pressure Sentra 1.8 : 192 psi
Open your hood and locate the upper radiator hose coming from the top of your radiator. this hose should go straight to the thermostat housing. You will need to drain the radiator and remove the hose. there should be three ten millimeter bolts hold it on remove the bolts and replace thermostat.