What can cause overheating in a 2000 pontiac sunfire

Sounds like you have a leaking head gasket or damage to the engine from when it overheated.
A leaking head gasket can cause compression to leak into the cooling system and pull coolant into the cylinders which is burned out the exhaust. It does not have to leak into the oil.
A shop would check for exhaust gas in the cooling system and run a compression test on the cylinders.

hello! I had the same problem with my 2000 Pontiac Sunfire... there might be one of these 2 problems with it.... maybe the Heater Core is jammed and the coolant dosen't flow thru the engine to cool it off, or the water pump is defective.... does the heating works or not? if yes, the water pump is defect, if not, the heater core is jammed, try a ''radiator hose cleaner'' (sold in Napa's or Carquest..) it will act as a kind of ''decloaker''.. if works, good! 15$ solution... if not, replace Heater Core... ~150$

I would start by replacing that section of hose. Depending on how much it's leaking it could be the source of the engine overheating as well. After it replaced make sure coolant level is where it's supposed to be. Hope this helps

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Thanks for the vote, and good luck!

Your coolant leaked somewhere, look for leaks. Hopefully it isn't the head gasket,.

I would flush the radiator and replace the thermostat, this should fix your problem

There is no radiator cap on the Northstar engine.
The only cap is on the surge tank (or expansion tank) and is pressurized.

So the answer is Yes, a faulty surge tank cap will result in the loss of coolant and therefore lead to overheating.

The most common overheating problem with the Northstar engine is a blocked purge line(small hose).The purge line is designed to purge air out of the cooling system.
There is a small diameter hose coming from near the top of the coolant tank (not the cap) ,this is the purge line.
With the engine idling,pull the purge line from the tank,if there is no coolant flow from this small hose,it is blocked and this will cause overheating.
If the hose is clear, check for blockage at the nipple on the tank.Or trace the hose back until you find the blockage.
The hose goes in to the engine to a crossover and comes out the other side close to the thermostat housing,the blockage may be there.

if your not losing coolant then id try replacing the thermostat.

if your not losing coolant its either a blockage or bad waterpump and more than likely its the water pump

leave the overflow tank cap off and start engine. turn your heater setting to max heat and fan on highpour 50/50 mixture of coolant till you see the coolant at the proper level on the tank. wait for the vehicle to reach optimum temp about 180 degrees. you should feel; the upper radiator hose it should be hot. then check level of coolant in overflow tank fill to proper level if neccessary. A quick note if you continue to lose coolant and can;t find a leak chances are it's being burned in the cylinder and this would mean you have a blown head gasket. to check this just start the vehicle the next day if there is white smoke yo have a seeping gasket if it's a constant white smoke then it's a severe problem and needs to be repaired immediately or you will warp or crack the intake manifold , the head or the block.. please rate this........thanks