2000 Pontiac Montana temperature gauge stays at zero

Have you checked your cooling fan to see if it is working propely? Let the car idle and get warm and listen for the fan to kick in (if they are electric) or just watch to see if the fan starts to spin faster if it is the old school type with a clutch. Have you replaced the thermostat? A bad one will let the temp rise since it opens too late and then the temp will drop off. But it won't due this only at a light and it will do it infrequently.

Watch the temp gauge when the electric radiator fans come on. The temp sensor that controls when the fan comes on may be faulty.

Most of the time the temperature sending unit is bad. If the check engine take the vehicle to Autozone its free to get a check engine light test. Or your local shop. Then we can go from there. Good luck!!!

Check your cooling fan motor at radiator, should come on at about 220 -225 deg, while moving you have air blowing through radiator and will keep engine cool, at stops no air going through radiator and will cause over heating. Have fan check out

This can be a sign that your coolant level is not adequate. It can also be a sign that your Temp Sending unit is bad. Oviously the first thing I would do is to go through the coolant level check of pulling the radiator cap (on a cold engine) and adding a mixture of 50% anti-freeze, and 50% distilled water until the coolant fills to the top. I typically run the engine with the radiator cap off until it gets to or close to full operational temperature (typically 190-210). When close you should see that the level has dropped after the thermostat has opened and circulated the coolant. Add additional fluid until the level stabilizes at the top again. Once it stablizes at the top replace the radiator cap. Check and make sure the temp gage is reading normal operating temperature. If you only have a light make sure it is not illuminated. You should know this better as you are used to driving the vehicle. If there is still in indication problem then look at other things like the temp sending unit. This is normally found screwed into one of the cylinder heads with a wire coming out of it. One way to check it is an ohmeter to the connection terminals. They don't cost but $15-60 dollars.
There are others issues that can be going on like a bad/worn or broken water pump drive belt (accessory drive belt, serpentine belt), or a bad water pump generally noted by coolant leaking out of weap hole on the bottom near the input drive where the pulley is at. There are other issues that could be causing this, but we won't go into those here (assuming your vehicle hasn't shown more serious indicators).

How do you know the thermostat is ok? If in doubt replace it. Water pumps are a even bigger what if. Did he do a radiator flush? Cooling system flush of the engine? Cooling fans come on at what temp and go off when? Replace the engine temperature sensor? 6 years old is bound to have sensors and such go bad.

Check the heat gauge sending unit. Or "engine coolant temperature sensor" as they call them these days. ECT. It should be somewhere near your thermostat housing. I hope that's the problem. Good luck.

tran should be ok need to take head to repair shap and be sure head is ok and not cracked. thermostat, radiator, or cap, hoses need to be checked to dtermine what caused it to run hot also check engine fan. Pls rate this solution

Check to make sure your thermostat works right by monitoring the warming up of your engine. With a completely cold engine, start and run the engine for a few minutes, then put your hand on the top radiator hose to monitor if and when it gets warm as the thermostat opens more and more and note the gauge reading( if it works) the top radiator hose should be unbearably hot within 5-8 minutes. If the therm. opens right it should close right aswell, staying open a little while eventhough the radiator may have cooled may be what you are experiencing causing the rapid cooling and is nothing to worry about. The Hose should not get warm very soon after starting the engine. Regarding you gauge, lets take one step at a time, verify proper op. or the therm.

hi from uk from your symptoms of what happened re temp guage risen suddenly it would indicate the temp sender unit on the engine has blown ie is earthing to engine via its screwthreaded body this is just a matter of replacing with a new sender unit hope this helps