2000 Nissan Maxima • 239,215 miles

I went to a workshop the person check the computer of my car. Then he tell me the error. The knock senser want to change but I recently change the the half engine because the oil and water of engine is mixied before few weeks
but the car still over heating another thing is that sometime is working good in both condition AC and with out AC is their the problem is related to electrical wiring or something else. The both fan is working good.I remove the both thermostat because of overheating. Plz tell me I am in serious Problem. The modle number is 2000 maxima middle east modle ok.
September 20, 2011.

Have you had the radiator checked for a part blockage, you may have several core tubes blocked restricting coolant circulation.

Sep 20, 2011.
Plz tell the parts which is to be change for heating up problem ok as I erlier mensyion. So it is for me to solve the problem.

Sep 24, 2011.