2004 Pontiac Montana just starting overheating. Temp gauge goes to the 1/2 mark in about 10 minutes after starting; When heat is turned all the way up, there is a loud humming noise which stops when heat is turned off. Also once van gets hot, there is a strong coolant smell and steam from the front hood.

Do the cooling fans come on ? Your best bet ,take your vehicle to a qualified repair shop . Does not sound like you know anything about automotive diagnostic's

Turn key on but do not attempt to start. Wait 10 minutes. Turn off. Then on. Make sure security light goes off before trying to start. Sounds like security system thinks vehicle is being stolen

3.4L Engine Sensor Location Pictures and Comments

www.greatautohelp.com/sensor-location/3400-Sensor-Comments-2.html
the battery for a few minutes to see if that helped. ... If the gauge is at half way on the first start, then yes, either the ... All of a sudden I could not accelerate and the carelost power. ... But once the temperature gauge goes to normal it will run fine. ... 3-7-12. I replaced head gaskets and intake gaskets on my 2000 Pontiac 3.4L

[PDF]2000 Pontiac Montana Owners Manual - GM Extended ...

you have a GM common problem and that is a bad intake manifold gasket. GM change the gaskets to plastic and they crank and leak causing over heating. here is a picture of one i took from a 2005 pon. bonneville with 74,000 miles on it

Sounds like a bad stepper motor in the instrument cluster. These are known to go bad. I had the same issue with my speedometer. Found the part on EBay for around $10. The hardest part with replacing it is that you have to unsolder the old one from the circuit board and then solder the new one on. There are a few good DIYs online that show you how to do it step by step. -Scott

Sean I have a 2004 Montana and mine is also overheating. I just paid Pep Boys $300 to replace thermostat and it is still overheating. They checked for coolant leaks, water pump is okay, the pressure checked out ok. No air in the system, etc. Today I brought it to a different mechanic and he says my cooling fan is kicking in very slow after the temp gauge goes 3/4 up which is not supposed to happen. My fan does not have a relay and he said it is either the temperature sending unit, but most likely it is the COMPUTER which is going to a very, very expensive repair. He said this happens a lot with Montanas! I am pissed. I just bought it used and the previous owner probably dumped it b/c he knew it needed a computer. Also the Fuel gage does not work and it will cost $800 to replace the fuel tank which contains the fuel sensor.

Check the belt at the water pump to make sure that everything is tight and rotating properly. Usually if a water pump goes bad it will start leaking out of the weep hole. Make sure that your fluid is full and that the mixture is correct (50/50). If fluids are good, belt is tight, your thermostat is probably stuck closed. If the temp outside is below freezing and you have too much water in the system, it may have froze up.

Yes that is cool if it's correct. 195 F is approx.as low as you should have. I'd change it. Be sure to run with cap off, and heater on (not defrost) while refilling system. Wait for rad fan to come on 2 or 3 times before you put cap back on, then add coolant to return bottle as needed. Make sure rad fan only comes on when up to normal running temperature. If it runs all the time, it may be causing low coolant temperature too.

check the thermastat

Its definitly a bad reading, you would know if your vehicle is overheating, you can usually smell it right away.I would say its your temperature gauge sending unit is defective, check the wires to see if they are well connected or broken. ask a backyard mechanic for assistance.