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TL;DR my 06 tC is very quickly overheating at seemingly random times after driving just fine for a while, and then the temperature immediately goes back down after stopping for a few seconds. So far I have replaced the thermostat, radiator cap, serpentine belt, water pump, and both radiator hoses have been checked and seem to be fine. Also, I have done a compression test on each piston and they are each making 150+ pounds, so no head gasket issues.
Here's some more details:
Right before I went back to college after Thanksgiving break, I replaced the serpentine belt on my car.
About an hour into my drive back while going up a hill, the radiator hose blew off and sprayed antifreeze everywhere. I wasn't paying attention to the temperature gauge at that point, but after I quickly saw it was overheating and pulled over, put the hose back on with an additional hose clamp, filled it back up with coolant, and went the last 4 hours with no issues.
At college, I drove it around a little with no issues, nothing more than 5-10 minute drives though.
On my trip back home, everything seemed fine, but then I stopped at a gas station 3.5 hours in and my car overheated again shortly after I got back on the road. I stopped and let it cool down (which took a while) and then went another hour until it overheated again. This time I stopped and unscrewed the radiator cap a bit after it cooled, and that barely got me the last 30 min drive home.
At home, the overheating had become normal, as the temperature would start to abnormally climb. It would still take a while to cool down, however. I then replaced the thermostat and radiator cap. These seemed to help, but did not solve the problem. The car would still overheat, but now randomly and quickly, and would go back down just as quickly after I let off the gas and/or stopped for a few seconds. It takes big hills just fine, but then it will overheat on a flat road at 35 mph. The heat also seems to go out when it is overheating, even though there is plenty of coolant. The only pattern I can think of is that its more likely to randomly overheat when I start driving before its warmed up all the way.
I did a compression test on each piston and found no problems, as well as replaced the serpentine belt (again) and the water pump yesterday, but the same thing happened again on my drive to work this morning.
The only thing left in the system to replace is the hoses (which I looked at and seem to be totally fine), the radiator, and maybe the a loose connection in the temperature sensor? I have never been able to recreate an overheat in the shop so I don't actually know if its overheating, but when it does start it seems correlated to how hard I push the gas pedal, so I doubt its the sensor.
Any time I put coolant back in I ran the heat at full blast and got all the air bubbles out, so its not that either.
I'm a broke college student running out of money and options, please help. Thanks for your time!
 

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TL;DR my 06 tC is very quickly overheating at seemingly random times after driving just fine for a while, and then the temperature immediately goes back down after stopping for a few seconds. So far I have replaced the thermostat, radiator cap, serpentine belt, water pump, and both radiator hoses have been checked and seem to be fine. Also, I have done a compression test on each piston and they are each making 150+ pounds, so no head gasket issues.
Here's some more details:
Right before I went back to college after Thanksgiving break, I replaced the serpentine belt on my car.
About an hour into my drive back while going up a hill, the radiator hose blew off and sprayed antifreeze everywhere. I wasn't paying attention to the temperature gauge at that point, but after I quickly saw it was overheating and pulled over, put the hose back on with an additional hose clamp, filled it back up with coolant, and went the last 4 hours with no issues.
At college, I drove it around a little with no issues, nothing more than 5-10 minute drives though.
On my trip back home, everything seemed fine, but then I stopped at a gas station 3.5 hours in and my car overheated again shortly after I got back on the road. I stopped and let it cool down (which took a while) and then went another hour until it overheated again. This time I stopped and unscrewed the radiator cap a bit after it cooled, and that barely got me the last 30 min drive home.
At home, the overheating had become normal, as the temperature would start to abnormally climb. It would still take a while to cool down, however. I then replaced the thermostat and radiator cap. These seemed to help, but did not solve the problem. The car would still overheat, but now randomly and quickly, and would go back down just as quickly after I let off the gas and/or stopped for a few seconds. It takes big hills just fine, but then it will overheat on a flat road at 35 mph. The heat also seems to go out when it is overheating, even though there is plenty of coolant. The only pattern I can think of is that its more likely to randomly overheat when I start driving before its warmed up all the way.
I did a compression test on each piston and found no problems, as well as replaced the serpentine belt (again) and the water pump yesterday, but the same thing happened again on my drive to work this morning.
The only thing left in the system to replace is the hoses (which I looked at and seem to be totally fine), the radiator, and maybe the a loose connection in the temperature sensor? I have never been able to recreate an overheat in the shop so I don't actually know if its overheating, but when it does start it seems correlated to how hard I push the gas pedal, so I doubt its the sensor.
Any time I put coolant back in I ran the heat at full blast and got all the air bubbles out, so its not that either.
I'm a broke college student running out of money and options, please help. Thanks for your time!
Of owning one of the first 4 cylinder engines with aluminum heads, once an overheat, good chance of a warp head. Need to change the head gasket, but a head grind is a must. Yeah, I know you did a compression test, but did you do it when the engine was warm (could be leaking not in the cylinder but to outside)? If you're losing water, do you see "white" water vapor (not the early morning start "white" vapor) after the engine have warmed up? Sometimes you might even see rust around the end tail pipe or the spark plugs. You might also try a pressure test in your cooling system to see if it holds pressure. Does the radiator cap have a brownish film around it (which is oil) which indicate head gasket. BTW, if you drive for awhile with a bad head gasket leaking to the engine, may cause Catalytic failure due to anti-freeze covering the platinum, a killer cats giving that annoying cat below threshold.
 

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Of owning one of the first 4 cylinder engines with aluminum heads, once an overheat, good chance of a warp head. Need to change the head gasket, but a head grind is a must. Yeah, I know you did a compression test, but did you do it when the engine was warm (could be leaking not in the cylinder but to outside)? If you're losing water, do you see "white" water vapor (not the early morning start "white" vapor) after the engine have warmed up? Sometimes you might even see rust around the end tail pipe or the spark plugs. You might also try a pressure test in your cooling system to see if it holds pressure. Does the radiator cap have a brownish film around it (which is oil) which indicate head gasket. BTW, if you drive for awhile with a bad head gasket leaking to the engine, may cause Catalytic failure due to anti-freeze covering the platinum, a killer cats giving that annoying cat below threshold.
TL;DR my 06 tC is very quickly overheating at seemingly random times after driving just fine for a while, and then the temperature immediately goes back down after stopping for a few seconds. So far I have replaced the thermostat, radiator cap, serpentine belt, water pump, and both radiator hoses have been checked and seem to be fine. Also, I have done a compression test on each piston and they are each making 150+ pounds, so no head gasket issues.
Here's some more details:
Right before I went back to college after Thanksgiving break, I replaced the serpentine belt on my car.
About an hour into my drive back while going up a hill, the radiator hose blew off and sprayed antifreeze everywhere. I wasn't paying attention to the temperature gauge at that point, but after I quickly saw it was overheating and pulled over, put the hose back on with an additional hose clamp, filled it back up with coolant, and went the last 4 hours with no issues.
At college, I drove it around a little with no issues, nothing more than 5-10 minute drives though.
On my trip back home, everything seemed fine, but then I stopped at a gas station 3.5 hours in and my car overheated again shortly after I got back on the road. I stopped and let it cool down (which took a while) and then went another hour until it overheated again. This time I stopped and unscrewed the radiator cap a bit after it cooled, and that barely got me the last 30 min drive home.
At home, the overheating had become normal, as the temperature would start to abnormally climb. It would still take a while to cool down, however. I then replaced the thermostat and radiator cap. These seemed to help, but did not solve the problem. The car would still overheat, but now randomly and quickly, and would go back down just as quickly after I let off the gas and/or stopped for a few seconds. It takes big hills just fine, but then it will overheat on a flat road at 35 mph. The heat also seems to go out when it is overheating, even though there is plenty of coolant. The only pattern I can think of is that its more likely to randomly overheat when I start driving before its warmed up all the way.
I did a compression test on each piston and found no problems, as well as replaced the serpentine belt (again) and the water pump yesterday, but the same thing happened again on my drive to work this morning.
The only thing left in the system to replace is the hoses (which I looked at and seem to be totally fine), the radiator, and maybe the a loose connection in the temperature sensor? I have never been able to recreate an overheat in the shop so I don't actually know if its overheating, but when it does start it seems correlated to how hard I push the gas pedal, so I doubt its the sensor.
Any time I put coolant back in I ran the heat at full blast and got all the air bubbles out, so its not that either.
I'm a broke college student running out of money and options, please help. Thanks for your time!
That's the thing once it's overheated once, the headgasket is more likely damaged. Have you tried picking up a headgasket test kit?

Anyway get your thermostats replaced every 5 years with OEM thermostat ..(third party thermostats are not made well). Paying for a $20-$25 thermostat every 5 years and coolant is a good way not to overheat your car. What I've been told that a majority of headgasket issues are caused by stuck thermostats. ...

check out this video from Faye Hadley ...
 

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I wonder if it might be an issue with the coolant not being burped probably and if the issue is actually a bunch of air bubbles in the cooling system that is causing it to appear random—just a thought but maybe worth looking into before spending more money.
 

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I wonder if it might be an issue with the coolant not being burped probably and if the issue is actually a bunch of air bubbles in the cooling system that is causing it to appear random—just a thought but maybe worth looking into before spending more money.
Actually that seems very possible that it was not completely burped when I think of it. Maybe there's stubborn air stuck in... I don't normally worry about it since I use a vacuum refiller ... also have you flushed out the system a few times with distilled water a few times til it's clean water? Are you using a big coolant funnel like this in this video done by Faye Hadley?

here's a video of Faye using a vacuum coolant refiller
 

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If compression is good, head is probably good. Keeping on driving with overheat is what warps. If you stopped immediately, you probably saved it. You replaced the belt and then the cooling system over-pressured and blew a hose. That could be a combination of tensioner and radiator cap (which vents pressure). When you have cooling issues its best to replace everything. OEM constant tension spring clamps for hoses are superior to after market screw hose clamps: its worth the cost. Tell me if you had screw clamps. I would test the serpentine tensioner and replace if not in spec. Replace the thermostat (OEM definitely, or quality like mishimoto), the water pump, flush it all and get a new radiator. The cabin heater core usually has crud in it and is difficult to flush. If you are digging down to water pump and thermostat, its a good time to replace idler bearings as well, they are 16 years old now.
 
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