I had a weird problem happen yesterday, I was driving the car and when I got home and parked, I noticed there was smoke coming from the engine bay. So I lifted the hood, and saw the coolant had overflowed from the main fill in tank, smoke was caused when the coolant spilled over on the hot metal. Also the metal cap was shaking and rattling for a while until the car cooled down again.

The AST looked fine, and the reservoir tank behind the pass. headlight was full to where it's supposed to be.

What's weird is that as this was happening the car was running perfectly fine, and water temps were in the mid 80's as they always are. I did push the car hard a couple of times on the way home but for no more than a few seconds. And even after that the car was running perfectly, idled fine, reved fine, vacuum was fine.

Do you guys think it might just be that the cap came loose and the coolant was overflowing, or could there be another underlying issue that built up to much pressure?

 

If the cap was loose the system wouldn't pressurize correctly and the car would have likely overheated. After it cooled down how full was the overflow tank?

 

The overflow tank is full. The main tank is of course empty from the coolant that spilled. I don't know when exactly it started spilling coolant because the steam would've blown away and go unnoticed while driving around.

Maybe the cap came loose right as I was getting home so there wasn't enough time for the car to start overheating.

 

If you want to be smart and escape a possible rebuild replace all your caps (ast and filler neck) and if you haven't yet, replace the factory ast. Do it.... NOW!!!

 

I had a similar problem last summer. I had a coolant leak on the upper radiator hose and my filler neck cap needed to be replace. BTW I don't have the ast.

 

replace your caps, check all hoses for leaks, burp out any possible air bubbles.
replace the AST with an aluminum one, even if yours looks fine. (assuming its the stock one)

all together youll spend less than $200, which is well worth the piece of mind that you're less likely to accidentally cook your engine, since a rebuild will costs you $2500+

its getting to be summer soon, better safe than sorry!

 

I have an aftermarket AST. I went through every hose and there's nothing leaking, but I burped the cooling system when I re-filled it.

So yeah I'm gonna replace the AST cap and the filler cap right away, thanks for the helps

 

I had the exact same experience. Both radiator caps not sealing properly (internally) was the fault! If you have no pressure in the coolant system, you will have a lower boiling point.

 

Well....let's all talk about the elephant in the room...too. What the o.p. is experiencing is also caused by failing internal 'O' rings which allow combustion pressure to enter the cooling system and force coolant out the overflow. It is the start of the 'slow death' so many of us have known so well.....

 

I didn't have coolant spilling out of the overflow tank though, my coolant spilled out of the main fill in neck.