No heat

i have a 2004 monte carlo, less than 2 years ago i had a new thermostat,water pump and serpantine belt put on, noe when i drive the heat only works at speeds above 50 mph

Can’t connect work done 2years ago with a problem today

What is the current coolant level?

coolant level goes up and down

Explain that, please? How does it go up and down?

It should remain constant unless there’s a leak, in which case the coolant level will go down. I don’t see how it can go up unless you add coolant.

I suggest the cooling system is not full, but instead has an air pocket somewhere, which you need to purge.

How are you judging the cooling level? It will appear to go “up and down” if one is looking at the overflow reservoir. It is down when cold, up when hot.

You first need to check the actual coolant level. With the car cool, remove the radiator cap and check (cover the cap with a big rag as you remove it, just to be on the safe side).

If your coolant level is fine, that leads me to the 50 mph part not really making sense. The car’s speed and its ability to produce heat are unrelated (engine rpm might be a different story, but not by a lot).

So…are you sure that it isn’t that you blower fan is out? I.e. your heat might be fine, but the fan that blows the heat might be out for some reason. Then, the speed of the car would go along with more fresh air being forced in through the vents.