No heat!

Hi I'm new around here. I just have a question for you. My S10 is blowing cold air/warm air and the temperature guage is jumping around a bit too. If the truck blows cold air the temp guage shoots up, but when the truck decides to kick warm air the temp guage drops back down to normal.
Since I'm in the frozen tundra of Canada, I'm just wondering if it's possible that my truck is just cold and once it thaws out the thing will start functioning normally again? My block heater isn't working (that's being fixed) so the truck hasn't been getting plugged in. Would that make a difference?
Thanks for the answers!

Laura

Your description of the guage makes one think that the thermostat is hanging up however, when was the last time you checked your fluid levels? Low coolant, the heater will be the first to quit and then the temperature will rise. Since you are getting a new block heater installed, I'm sure they will top off the coolant and then you will see what happens.

I had to backflush my heater core this year because my heat quit working. I just disconnected the hoses and ran water into the right side port. Work great now. I don't recall my temp gauge jumping around though. As Mikado said, might be a thermostat problem.

I'd almost think that your coolant isn't quite strong enough, and turning into a gell.

If you have a v6 motor you might be better off installing an in'line block heater since they just go from a block drain plug up to a heater hose ( much easier to install on my truck ) Plus they partly warm the cab up while plugged in since they are always circulating the warmer fluid through your heater core. Although they cost way more. I spent pretty much 100 bux canadian for everything just last month