You've done most of the things that would normally caused overheating. I assume that the thermostat was installed correctly. One other possibility is that the lower radiator hose may need to be replaced. I suspect that you still have the original hose. Sometimes, old rubber hose like that would collapsed during high engine load thus preventing the coolant from circulating. On some cars, the manufacturer would install a metal spring coil to prevent this from happening. I'd go ahead and replace these hoses. It is about $25 each (CourtesyNissan has them for 18.00 each.
FYI, when coolant is circulating, the water pump sucks the coolant from the radiator thru the lower hose, then pushes it up to the engine and back to radiator via the upper hose.
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Thursday, June 17th, 2010 AT 8:02 PM