My Trans Am, Which I bought about 10 months ago has always run around 210 to 230 degrees and it kept me paranoid with all the aluminum and plastic. Yesterday, out of the blue the temp rose to 250! Scared me pretty bad so I started tearing everything apart. After scratching my head for hours I filled my overflow reservoir to the top and ran the car till it heated up pretty hot and noticed there was absolutely no activity from the reservoir. I pulled the battery and overflow tank and sure enough, the battery had corroded the line till it was totally blocked, I pulled the tank, flushed it out really well, replaced the hose and today after topping it off with coolant I drove it down a street that had lots of traffic and red lights and the hottest it got was 217 degrees. on a not so busy street, with a 186 degree thermostat, I'm running between 197 and 207 degrees. I hope this can help someone with similar problems down the road!

 

I'm not seeing how a blocked overflow line is going to make the car overheat.

 

Agree. It won't. Unless it was low on coolant in the radiator and fixing the tube allowed it to draw in some coolant and top itself off. Which just means the real issue was that it was low in the first place.

 

Good to know that the line can corrode there. I'm not 100% convinced that the line being blocked was your problem either though. That being said I could see where you flushing the system probably made the real difference. Be sure to check/replace your thermostat too. It might have been stuck closed (or partially closed) and you got it freed up.

 

Now that I agree with. That's actually the exact same thought I had.

But that was not mentioned in the first post by the OP.