2008 Cobalt overheating

csheridan

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This has been the worst experience with a vehicle I have ever had:

I purchased my 2008 from an independent seller. I mistakenly drove it 20 miles back to my house low on coolant. It overheated. Come to find out, the lower radiator hose clamp was loose at the radiator. Then my nightmare began.

I've been laid off, and I'm due to report back to work on June 6th. I've had the car since February. Since I overheated the engine, I blew the head gasket. I mistakenly took it to a dealer (never again), and they said I needed a catalytic converter because it was throwing a code (catalytic inefficiency). That cost me $100 for them to tell me nothing.
About 2 weeks later, it started blowing white smoke. Head gasket. I replaced the head gasket and timing chain (I was already there. Couldn't hurt). It ran beautifully, no codes, no misfiring, no white smoke. I thought all was well until the temp kept rising.
Well, I bought a heater core and replaced it, as well as the two molded hoses.
While it was apart, I tested the thermostat (new one) in water, and it opened as it should have.
My fan kicks on as it should, but the temp just keeps rising. I always turn the car off at 230°. I don't want to cause another problem.

(I have Dexcool in the engine btw)

I'm at my wits end, and I'm running out of time because work is 12 miles away and I start back in less than two weeks. I can't afford a mechanic, plus I used to be one, so it saves me money to do it myself.

I even replaced the expansion tank cap (no radiator cap). What am I missing here?

It runs great, and doesnt throw any codes, but it's getting warm while idling in my driveway, and the heater is not blowing hot.

Please help, thanks.
 

YelloEye

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Wow, sorry for your troubles man. Some dealerships are shady when it comes to extra repairs. I have a couple thoughts on what the issue could be from what you are describing, nice job on that by the way.

First is the system free of air bubbles?
There is a burping procedure but it is really basic and should be fine at this point after you replaced the heater core and drove her for a while.
  1. Start the engine.
  2. Run the engine at 2,000-2,500 RPM for 3 minutes. (This should open the thermostat)
  3. Allow the engine to idle for 30 seconds.
  4. Shut the engine off.
  5. Top off the coolant as necessary.

If there are no air bubbles, it sounds like you aren't circulating coolant. There are basically 2 reasons for that that come to mind for me, either the water pump isn't doing its job, or the thermostat isn't opening.

You stated in your original post that you tested the thermostat. I don't mean to be insulting with this next question. Is it installed the correct direction?
I've only done one thermostat on these cars and don't recall if it even can be installed backwards.
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If everything else above is good, then I'd say the water pump either isn't spinning or maybe the impeller fell off the back side?
When you did the timing chain, did you also notice if the water pump was hooked up? It runs on the balancer chain on this motor.
 

csheridan

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I don't think it can be installed backwards either. It wasn't insulting at all to mention that. It's a simple mistake. But yes, it's installed just like the diagram shows.

When I had the front cover off, the balance shaft chains appeared to be correctly on the water pump sprocket. I touched nothing but the cam sprockets and crank timing chain. To be honest, I was so focused on the job at hand that I didn't look particularly close, but as far as I know it was ok.

Hypothetically, if the water pump is bad, it makes me wonder if it was bad to begin with and the coolant leak was just a coincidence.
When it was still driveable during winter, it only overheated intermittently. Now it's constant. I'm afraid to drive it, so any procedures have been in my driveway at idle.
 

csheridan

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What sucks is that I can't even take the water pump off until I have the GM tool. I'd make one, but I don't have any flat stock or a drill.
 

YelloEye

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For the guide bolts you just reuse the 4 plate mounting bolts.
 

csheridan

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Ok. I was looking in my Haynes manual and it shows a fabricated tool with guide bolts.
I need this fast, and a Google search actually showed Walmart to have it (weird since AutoZone, O'Reillys, and Advance didn't have it). Gonna snag a ride asap and see if I can find it. If not, then I'm overnighting it online.
Once I get this apart, is there a way to check/inspect the pump before I throw another part at it?
 

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