I changed my thermostat twice in a week on my 2008 Pontiac vibe. My car was blowing cold air and running hot but the thermostat would open up and it would go back down to normal. I would have heat for maybe three minutes and then it would be blowing out completely cold air again. I had a radiator flush and also flushed my heater core. What would be your suggestion. Possibly a new radiator or water pump?

  • Do you know roughly how many miles are on the car?
    – cdunn
    Dec 8, 2016 at 21:26
  • 1
    I'd probably try bleeding the system again before you replace more parts. Use a spill free funnel, fill it, leave the funnel on with the cap off... and hold the engine at 2500-3000 rpm until the radiator fan comes on then recheck the coolant level.
    – Ben
    Dec 8, 2016 at 22:08
  • I second @Ben's thinking...I think this is called "burping" the radiator. In other words, they may not have replaced enough coolant after they flushed your system. Might sound negligent (and it is), but it may not be uncommon...it's happened to me...definitely watch the linked video.
    – elrobis
    Dec 9, 2016 at 20:20
  • This might be a better video with respect to explaining the issue, the thinking, and some how-to tips.
    – elrobis
    Dec 9, 2016 at 20:27

2 Answers 2


Since you've flushed the system, we can assume the coolant is free to flow where it should. It could very well be that your water pump isn't circulating your coolant very well anymore.

First make sure the belt is driving the pump properly (make sure the belt isn't loose). If the belt looks good, a new water pump shouldn't be too expensive or too difficult to change at home. If your coolant is still in good shape (it should be new, since you've had the system flushed) you can reuse it. Just drain it in a clean container and use a paint filter to keep particulates out when you put it back in.

A new radiator is only needed if the old one leaks, is severely rusted, or is completely blocked. You would have noticed a blocked radiator during your flush.

  • Roughly 149,000 miles. Never once had any issues in the 2 years I've had it. I got a water pump and am going to try that tomorrow. Haven't checked the belt. So I'll do that as well. Another thing that happened after I did all of this, was the fact my temperature gauge will go all the way up but yet it's still not actually overheating. I don't understand it. Still freezing cold air which the gauge goes up and down.
    – Sarah
    Dec 8, 2016 at 23:22
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    Make sure you get all the air out of the system when you're refilling it. Find all the bleeder screws, squeeze the upper rad hose a bunch of times, etc.
    – tlhIngan
    Dec 8, 2016 at 23:24
  • Thank you all for the help. I've tried all of these options and ended up taking it to a Pontiac dealership to have the service department work on it. No bleeder screws. They have tried bleeding the system out for 3 hours and they can't seem to get the air out. Doing tests to check the head and intake next. Anyone want to buy a vibe?! 😂
    – Sarah
    Dec 10, 2016 at 20:13
  • Didja change that water pump?
    – tlhIngan
    Dec 11, 2016 at 23:22

Based on what you've said, I'd suggest looking at the heater core, it may be blocked or something may be restricting flow through it. The reason I think this is happening is that you mention that there is some initial heat, but then it turns cold. That would happen if there was minimal flow through the heater core. It would warm the air when the fan was first turned on, but then the air would cool down the core and there would be no more heat.

You can test this by turning off the fan for a while and checking to see if there is heat again when you turn it back on.

If the problem is air in the system, one way to get it out (given the lack of a bleed screw) would be to open the highest joint in the system and then pour coolant into the hose until it is as full as you can get it. But I'm not convince it is air in the system – if it was air that was restricting/blocking the flow I'm not sure if you would ever get heat.

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