Questionable cooling issues

[beachbum12tree]

ok so I have read read and read about people talking about their radiator overflow bubbling up and engines overheating. But my issue is just slightly different. My temp gauge doesn't tell me that the engine is overheating.
While driving on the freeway my scangauge tells me my water temp is 186.
It never goes higher, even after hefty spirited driving.
But when I stop and turn the car off, my overflow tank fills up with fluid.

Now I pulled off the radiator cap and started engine and ran the heat on high and let the fans go through 3 cycles or so to burp the system of any bubbles.
Problem went away for a few days and then started up again.

My question is, do I have a faulty radiator cap, or does this still fall under a faulty t-stat?

Oh, don't know if this is any help, but my a/c currently isn't working. I have a cracked condenser to compressor line.

 

[slavrenz]

ok so I have read read and read about people talking about their radiator overflow bubbling up and engines overheating. But my issue is just slightly different. My temp gauge doesn't tell me that the engine is overheating.
While driving on the freeway my scangauge tells me my water temp is 186.
It never goes higher, even after hefty spirited driving.
But when I stop and turn the car off, my overflow tank fills up with fluid.

Now I pulled off the radiator cap and started engine and ran the heat on high and let the fans go through 3 cycles or so to burp the system of any bubbles.
Problem went away for a few days and then started up again.

My question is, do I have a faulty radiator cap, or does this still fall under a faulty t-stat?

Oh, don't know if this is any help, but my a/c currently isn't working. I have a cracked condenser to compressor line.

You're going to have to describe your issue a little bit better, because it sounds to me like your cooling system is working properly. As the coolant gets hotter, it increases in pressure, until finally it spills over into your overflow reservoir. Thus, after a long stint of spirited driving, you'd expect to find more coolant in your overflow reservoir than if you just moved your car down the block.

Am I accurately describing your situation?

 

[beachbum12tree]

So far so good I guess. So what ur saying, is that it's normal to see your overflow tank full up after extended periods of driving, spirited or non spirited?

 

[slavrenz]

So far so good I guess. So what ur saying, is that it's normal to see your overflow tank full up after extended periods of driving, spirited or non spirited?

Yes. Your cooling system has a fixed amount of coolant. At low temps, it's all in your engine block and radiator. However, at higher temps (such as those experienced during "spirited" driving), the coolant temp shoots up to almost 200 degrees. This causes a huge increase in pressure, and all that extra coolant's gotta go somewhere, or else it'd blow of your hoses and ruin your gaskets.

The radiator cap has a spring built into the bottom which, at a given pressure, compresses and opens up a channel in the radiator neck that leads to your overflow tank - this is where all that extra coolant goes. I've never popped my hood immediately after sustained heavy driving, but I'm sure my overflow reservoir would be like yours.

Later, as your engine cools down, the coolant in the overflow reservoir moves back into your engine block, due to the lower pressure, via a check valve in the radiator cap.

Unless your coolant is actually boiling out the top of your overflow reservoir, and you're not smoking, I'd say your fine. You could try replacing your coolant temp sensor, but I don't think it'll change anything.

 

[CheeseHelmet]

How much does your overflow tank fill up? Mine will jump up about 4-5cm after regular driving (which is why they put the FULL line around the middle of the bottle).

 

[i12drivemyMP5]

Same here, coolant expands and fills the bottle more than if you look at it when it's cool but not fill it completely up. Cheapest, easiest thing to do is pop in a new T-stat and see how it acts. Move on to something else if same thing is occurring. If the t-stat is hanging open a bit too long then water flows too fast to get cooled properly. It could be doing it enough to get your attention but not bad enough to overflow on the ground.

 

[beachbum12tree]

When cold, my the fluid level in my overflow tank is at the full mark.
This pas weekend I drove about 75miles, all highway at about 75-80mph; got home, popped the hood, waited a few minutes and the tank was definitely more than 3/4 of the way full.
But woke up the next morning and level was back to normal and car did run fine.
I am really just nervous some recipe for disaster is in the works that I'm oblivious to.

 

[CheeseHelmet]

When cold, my the fluid level in my overflow tank is at the full mark.
This pas weekend I drove about 75miles, all highway at about 75-80mph; got home, popped the hood, waited a few minutes and the tank was definitely more than 3/4 of the way full.
But woke up the next morning and level was back to normal and car did run fine.
I am really just nervous some recipe for disaster is in the works that I'm oblivious to.

Mine does the same thing, I don't think you need to worry.

 

[slavrenz]

When cold, my the fluid level in my overflow tank is at the full mark.
This pas weekend I drove about 75miles, all highway at about 75-80mph; got home, popped the hood, waited a few minutes and the tank was definitely more than 3/4 of the way full.
But woke up the next morning and level was back to normal and car did run fine.
I am really just nervous some recipe for disaster is in the works that I'm oblivious to.

What kind of disaster? Your cooling system is functioning perfectly.