Don't run your engine if the temp. gauge is up to the caution mark. Definitely don't let it idle like that, either. When the engine is cold, check the coolant level in your radiator. Add some if it isn't all the way full.
For coolant, just regular 50/50 mix coolant and distilled water or the pre-mixed 50/50 fluid.
If your fans are running, they are good and doing their job.
If you don't notice any abnormal noise, growling or whining, from the side of your engine where the belts are, then the water pump is more than likely ok. If it is growling or whining, from that side, do NOT run it anymore, as the water pump is probably on its way out.
A new radiator isn't likely to be clogged, so it is probably good.
However, when you change a radiator, air enters the cooling system and if it isn;t bled out, it causes the engine to heat up more than it should. It's easy to forget to bleed the air out and assume you are good to go after switching out the radiator.
You could ask a shop to bleed the air out of your cooling system. It isn't an overly involved process or difficult. You can probably even find How-To's on here.
I would bleed it just to rule out the air-in-the-line possibility. Look up the How-To or see instructions in your Service Manual and follow those directions.
It basically involves cracking the bleeder screw on the thermostat housing and unplugging the air release plug (at the highest point of the cooling system, usually seen as a black, rubber nipple on some small metal hose close to the firewall), setting heater to high and running the engine (once you've filled the radiator all the way). Once coolant begins to dribble out of the bleeder screw hole on the thermostat, you re-tighten it and top off the radiator until you see coolant running out of the air release pipe. Once coolant has started to come out of this pipe, you know the air is out of the lines because it is the highest point of the engine (where any air would run to). Turn off the engine, Cap the radiator and put the air release plug back on.
If you bleed out the air and it still overheats, I would say it sounds like your thermostat is sticking in semi-closed position, allowing some coolant through, but not enough to exit the engine fast enough. It should be changed if this is the case.
As a side note: If your temperature gauge fluctuates while you are driving, there is likely to be air in the coolant system or your engine temperature sensor is probably bad, or just not plugged in.
If the engine simply overheats, think low coolant or bad thermostat.
For diagrams for your Nissan engine, go to nissanpartsdeal dot com, and enter year make and model to find your vehicle's engine and various systems. Engine Cooling should bring up the right diagram for you to locate where things are on the engine.
