Depending on what kind of temps you're seeing, I'd suspect the thermostat, water pump, and/or coolant temp sensor.

It could also be clogging caused by incompatible coolant mixing. Your car should have come with HOAT from the factory, but it's very common for owners and even experienced service techs to put in OAT, IAT, or even [shudder] Dex-Cool.

 

I'd second your thermostat or water pump.

How could I tell if it's a blown head gasket? If I remember correctly, the temperature goes all the way to the red on the furthest it can go. The mechanic said he used the correct coolant and didn't say he used HOAT though. He did say that he doesn't have the vacuum to flush all the coolant out.

 

I'd second your thermostat or water pump.

 

You have a massive leak somewhere (probably the radiator itself--the plastic end caps crack when they get old) fill it up with plain water and watch to see where it goes while it is idling. (and the Zerex G05 is the correct coolant for pre 2013 models). The old 3.5 has lots of places where it can leak: radiator, water pump, hoses, heater hoses, heater core, the lower intake manifold gasket, or the head gasket. The lower intake manifold gasket is potentially deadly- it lets the lookant leak into the intake port and can hydro lock the engine (AKA kill it). The water pump is not visible (under the timing belt cover) and if it is leaking it will take out the timing belt and potentially bend the valves (look for water coming out the timing belt cover near the bottom (Video shows where it is and how to change it- it is a royal pain in the butt to do).

1st pic shows where the lower intake manifold gasket leak can occur, 2nd pic shows what happens when you use the wrong coolant..

 

fill it up with plain water

Can I fill it with water and still do the combustion leak test after?

 

AIO:
I see no mention of WHEN the car overheats. At idle, running down the road, or both? Does the cooling can come on at all? If so, when? Can you get it to activate right away by cranking the A/C up? As mentioned, all that coolant is going somewhere. Gotta figure this out as well.

Don

 

AIO:
I see no mention of WHEN the car overheats. At idle, running down the road, or both? Does the cooling can come on at all? If so, when? Can you get it to activate right away by cranking the A/C up? As mentioned, all that coolant is going somewhere. Gotta figure this out as well.

Don

Yes, I bought the test and I think it came out negative. I tried it on a hill, then my sister redid the test and the liquid remained blue both times, although when I tried the water/coolant did get warm hot.

 

Your overheating could be due to air trapped in the system. If it's losing as much coolant as you say, you would have to see a puddle, steam from under the hood, as well as smelling the sweet, sickly smell of coolant.

Don