2000 pontiac Montana... first I replaced thermostat and water pump and then radiator started leaking so I replaced that and now its worse

Try reverse flushing the whole system.

Questions:

. Did you install the thermostat properly?

. Did you purge the system of air and completely fill it with coolant?

. Does the radiator fan operate properly--check fuses; Engine Coolant Temperature (ECT) Switch, not the ECT Sensor; and radiator fan relay. The cooling fan not operating properly is one of the most common reasons engines overheat. If the coolant is low and/or there's air in the system, the ECT Switch may not turn the radiator fan on.

. Does the radiator shroud seal tightly enough for the fan to draw air through the radiator. This can cause the engine to overheat, while the vehicle is stopped.

. Has the aluminum head warped? Is there coolant in the engine oil? Is there white smoke in the exhaust?

Um... I a be a girl... so I didn't do it... lol anyway my dad and husband did it and they say yes, of course but it ran fine for a couple of weeks and then couple days ago , on my way 2 work, on the highway I noticed the temp gauge climbing quick... I got off an exit before it was in the red but it was darn close... I let it cool down for a while and checked coolants and my dad came and followed me to my house... my dad replaced the radiator today (he is a bit more mechanically inclined than my hub) but it seems worse... I did purchase a flush kit at auto zone is that what they need to reverese flush it? They want 2 know what reverse flush is, if you could... please and thank u

Reverse flushing is when you attach a garden hose to a properly installed "T" in the cooling system, open the radiator cap, slowly open the spigot, and allow the old coolant to come out of the radiator. The coolant is now flowing in the reverse direction from what it normally does. It helps break corrosion and blockages free.

Sounds like a plan about flushing the system... which hose do we put the T on? I just want to say your comments have been greatly helpful and I appreciate it Thanks so much

Ensure hoses are not collapsing shut.

Last, but not least, radiator caps sometime fail. There are sometimes two valves inside--one allows excess coolant to flow into the reservoir tank; the other allows the coolant to flow back into the radiator, when the system cools down.

Read the instructions that come with the flushing kit, since I'm not familiar with your engine. Frequently, the "T" is installed in the inlet line going to the intake manifold.

Once you solve the overheating problem, only use the proper 50/50 mixture of Dex-Cool and distilled water in the future. Tap/well water has way too many minerals in it that forms phosphate scale, when combined with antifreeze. This scale easily blocks off passages in radiators and heater cores. Otherwise, just buy the proper prediluted antifreeze.

Do not drive the vehicle, until you solve the problem. Allowing the engine to overheat, even once, can warp the aluminum head, damage the valves, and blow the head gasket. Repairs costs will likely exceed the value of the vehicle.

Yeah, we actually replaced the radiator cap first time around and then I lost it somehow so I put the old one on and then I bought a new one again... and put that one on the new rad... getting frustrating the van is nickel and dimin me 2 death

I know how that happens. These are about all the thoughts I can share with you--I hope they help.

Where would I find this switch

I have a 2000 pontiac Montana van and all over a sudden it started to over heat it went up to 260 and I pust coolant in it and it went back down I have a question will needing a oil change cause a problem with over heating

Only if you let the oil change go way, way overdue. Then, the ability of the oil to carry away heat from bearings and other parts is seriously compromised.

Most likely, you have not been changing the coolant every 30,000 miles, using a 50/50 mixture of DexCool and distilled water.