Coolant overflowed w/out overheating?

[joonsup]

Wondering if anyone can lead me in the right direction. I drove my car to work, then to the gym, and then home. Then after dinner I drove to my friend's place about 15 minutes away to put on some spacers.

I got there, waited in my car with the engine running while my friend opened the garage, then drove into the driveway. As soon as I got out I see a lot of coolant on the driveway running down towards the street. Seems to have come from the driver side underneath.

I opened the resevoir cap and saw the coolant level pretty high and you could see some smoke. It seemed like it overflowed because there was coolant around the resevoir. After a few minutes the coolant level dropped significantly almost to the bottom. I ended up adding more coolant/water to the proper level and let the car sit while I worked on the rest of the car.

The temp gauge always showed about a third, so I am a little confused unless my temp gauge is very inaccurate. This is the first time something like this has happened. I've taken my car to a couple track days and each time I checked the coolant level in between sessions I never had to add any.

a month ago I even drove down to socal and back w/out any overheating or coolant issues. Any order of what I should inspect/replace first? Cap? thermostat? fan clutch? etc...? any guidance greatly appreciated. Thank you

[u3b3rg33k]

"Nucleate Cooling Phase
As coolant flows through the system it absorbs heat from the engine parts that it comes in contact with. As it does this some of the coolant will boil and form tiny steam bubbles (absorbing a lot of heat in the process) on the internal engine surfaces. When these bubbles get larger they become a flow restriction and the flowing fluid pushes them away from the surface and that process starts over again.

The process is called the Nucleate Cooling Phase. When the coolant boiling point is too low or the flow rate is too slow, these bubbles can become too large and form steam pockets that insulate that surface from being cooled.
This usually happens around the combustion chambers, the hottest parts of the engine. Once the steam pocket forms the surface will rise in temperature (even though the coolant is not overheating) and cause that part to overheat, which can cause detonation and / or other problems."

http://www.grapeaperacing.com/tech/index.cfm

Does your cap seal properly? When was the last time the fluid got changed? If you've been topping it off with water, you're lowering the boiling point.

[jlevie]

Since there's no evidence that the engine overheated, the most likely cause of this will be air in the cooling system. In the absence of recent cooling system work (and a failure to fully bleed the system) the cause of air in the cooling system will be a leaking head gasket.

[Rolla1990]

I hate to be the bearer of bad news... Everytime this has happened to me it was the head gasket pushed into the coolant passage around cylinder 6.

[joonsup]

So is there anything visible I can look for once i pop the hood or is the only way of knowing for sure is to take it apart?

[jlevie]

There is fairly easy way to find out if you have a leaking head gasket. Fully bleed the cooling system (procedure below), drive the car for a bit, then re-bleed. Release of a significant amount of air on that or a subsequent bleed is evidence of a leaking head gasket. You can try one of the chemical tests for combustion gases in the coolant, but I've have inconclusive results from that.

1) Using ramps or a jack get the front of the car 1' or more higher than
the rear. That will make the radiator and bleed screw the highest point
on the engine and facilitate removal of air.

2) With the bleed screw open, add coolant until no more air comes out of
the bleed.

3) Leave the filler cap off, or at least loose, and set the heat for max
temp and fan speed. Leaving the cap loose will prevent air that's still
in the system from causing a "coolant fountain" once the engine heats
up. Start the engine and allow it to warm up to operating temp. As it
warms up occasionally crack the bleed screw to release any air and top
up the coolant as necessary.

4) Once the engine is at temp bring it up to 2000-2500 for a few seconds
several times. Then crack the bleed until no more air is released. At
this point the heater should be throwing lots of hot air, which
indicates that the heater core is filled with coolant. You may have to
repeat this a few times to get all the air out.

5) Drive the car a bit, allow it to cool back down, and recheck the
bleed for air. Over the next few days you may get very small amounts (a
few bubbles) of air out of the bleed screw.

[joonsup]

Thanks for the detailed write up. I'll tackle this this weekend and report back. Weird thing is that the previous owner said that he rebuilt the top end too, so I would have assumed he changed the head gasket. hmm

There is fairly easy way to find out if you have a leaking head gasket. Fully bleed the cooling system (procedure below), drive the car for a bit, then re-bleed. Release of a significant amount of air on that or a subsequent bleed is evidence of a leaking head gasket. You can try one of the chemical tests for combustion gases in the coolant, but I've have inconclusive results from that.

1) Using ramps or a jack get the front of the car 1' or more higher than
the rear. That will make the radiator and bleed screw the highest point
on the engine and facilitate removal of air.

2) With the bleed screw open, add coolant until no more air comes out of
the bleed.

3) Leave the filler cap off, or at least loose, and set the heat for max
temp and fan speed. Leaving the cap loose will prevent air that's still
in the system from causing a "coolant fountain" once the engine heats
up. Start the engine and allow it to warm up to operating temp. As it
warms up occasionally crack the bleed screw to release any air and top
up the coolant as necessary.

4) Once the engine is at temp bring it up to 2000-2500 for a few seconds
several times. Then crack the bleed until no more air is released. At
this point the heater should be throwing lots of hot air, which
indicates that the heater core is filled with coolant. You may have to
repeat this a few times to get all the air out.

5) Drive the car a bit, allow it to cool back down, and recheck the
bleed for air. Over the next few days you may get very small amounts (a
few bubbles) of air out of the bleed screw.