Coolant Reservior Boil Over Via the Evac Hose?

[TheHorse13]

I took a 2 hour highway ride (55-70 mph) in 90 degree heat and idled in stop-n-go traffic for 30 mins immediately after I got off the highway. As soon as I shut off the car, my coolant reservior boiled over forming a small puddle about the size of a dinner plate on the ground (I'm assuming that the evac hose on the coolant reservior was the way the coolant escaped because there is no mess of any kind under the hood). I never received a DIC message nor did I see any steam coming from under the hood. The only sign that something was going on was the puddle forming on the ground. Upon inspection, I heard what sounded like boiling water coming from the coolant reservior. The sound stopped a minute or so after I discovered it as well as the leaking coolant. There were no other signs of an overheat condition after inspection of the radiator cap and cooling system components. I also checked the engine temp with the engine off (it was sitting for about 2-3 minutes at this point) and it read 230 degrees. I understand that the temp will be 10+ degrees higher than the car was running once the engine is turned off. The only thing I could come up with is that perhaps the car was given a little extra coolant than needed from the factory and it just boiled over. I say this because I drove home in hotter conditions, with the AC running and the issue did not come back. I ran between 192-196 degrees the entire way. This was the first time the car was on a long road trip and it currently rings in with about 1500 miles. This morning I checked the coolant level after the car sat overnight and it was one level indicator above MIN on the cold engine marker. This translates into about half inch higher than the MIN marker.

Has anyone else seen this?

[Rock-It Man]

Originally Posted by TheHorse13

I took a 2 hour highway ride (55-70 mph) in 90 degree heat and idled in stop-n-go traffic for 30 mins immediately after I got off the highway. As soon as I shut off the car, my coolant reservior boiled over forming a small puddle about the size of a dinner plate on the ground (I'm assuming that the evac hose on the coolant reservior was the way the coolant escaped because there is no mess of any kind under the hood). I never received a DIC message nor did I see any steam coming from under the hood. The only sign that something was going on was the puddle forming on the ground. Upon inspection, I heard what sounded like boiling water coming from the coolant reservior. The sound stopped a minute or so after I discovered it as well as the leaking coolant. There were no other signs of an overheat condition after inspection of the radiator cap and cooling system components. I also checked the engine temp with the engine off (it was sitting for about 2-3 minutes at this point) and it read 230 degrees. I understand that the temp will be 10+ degrees higher than the car was running once the engine is turned off. The only thing I could come up with is that perhaps the car was given a little extra coolant than needed from the factory and it just boiled over. I say this because I drove home in hotter conditions, with the AC running and the issue did not come back. I ran between 192-196 degrees the entire way. This was the first time the car was on a long road trip and it currently rings in with about 1500 miles. This morning I checked the coolant level after the car sat overnight and it was one level indicator above MIN on the cold engine marker. This translates into about half inch higher than the MIN marker.

Has anyone else seen this?

Not on my Camaro, but it's typically a sign of a faulty or incorrectly installed radiator cap.

Have you ever taken the cap off?

[Jayrcr3]

When I installed my cam I accidentally overfilled the reservoir. After a few hot days I noticed a small puddle on the garage floor. Sounds like yours may have the same problem. After making a mess a few times, it hasn't happened since.

[TheHorse13]

Originally Posted by Jayrcr3

When I installed my cam I accidentally overfilled the reservoir. After a few hot days I noticed a small puddle on the garage floor. Sounds like yours may have the same problem. After making a mess a few times, it hasn't happened since.

No other issues have come up since the day it happened. I've also driven the car in worse conditions than the day the boil over happened and there have been no more boil overs. I've also checked the coolant level and it remains exactly where it was the day of the boil over.

The radiator cap has never been off the car. I've written this off as a one-time issue with the reservior being filled a little too much.

Thanks for the replies.