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. Thank you.
September 20, 2011.

Duplicated question

Sep 20, 2011.