i have a 95 Z28 M6. anytime i drive it for more than five minutes and shut it down, the antifreeze bubbles up and out of the top of the reservoir cap. it also leaks from another point, but i'm not entirely sure where (not the radiator). it does this until the reservoir is completely empty... however, nothing ever leaks from the radiator. at the time of the leaking, the temp gauge never gets past the halfway mark. thoughts?

 

Any recent activity with the coolant hoses? Your scenario sounds like the common mistake of switching the overflow hose with the steam line hose at the radiator. Another possibility is that you have a bad radiator cap.

 

no recent activity in the coolant hoses, although it wouldn't surprise me if there was a crack in one of them somewhere... would that make sense in this instance? any idea where i can get a diagram of the coolant hoses throughout the engine?

when you say radiator cap, do you mean the press-cap on top of the radiator? if so, it seems to seal tightly every time...

 

Shoebox is refeering to the cap on the radiator. Sometimes they go bad and leak.

 

i'm not sure i'm clear on which cap you're talking about... if your standing in front of the engine, facing the windshield, the cap i'm referring to is on top of the radiator, on the left hand side... is that what you're talking about? this is the one that you have to push and turn to release it.

thanks so much for the quick turn arounds.

 

Yes that's the radiator cap. It's designed to pressurize the coolant system to 16 or 18 psi. If the seal or spring has gone bad then the coolant system won't pressurize properly and can your coolant to overheat and generate your symptoms.

 

There is only one radiator cap and it is on the radiator. It would have to be pressure tested to be sure it is working properly.

All hose diagrams are on my website.

4th Gen LT1 F-Body Tech Aids-Drawings & Exploded Views

http://shbox.com/1/95-97_hoses.jpg

http://shbox.com/1/heater_hoses.jpg

 

thanks so much for the explanation/links! can you explain to me why the lack of a pressurized cap on the radiator would cause a leak in the hosing/reservoir? i'm curious as to how that would work/if i need to check all the hosing for cracks.... thanks again!

 

If high pressure leaks past the cap, it is going to go to the reservoir. It would be easy enough to just buy a new cap and see what it does. Any coolant going to the reservoir should be of a low pressure. The metal pipe going to the reservoir is prone to battery acid corrosion and leaks. You might want to check that out, too.

 

The cooling system needs to be pressurized to keep it from boiling. The cap holds 18psi. If the cap spring or seal fails and releases the pressure, the coolant can boil at temps as low as 232*F, and as the coolant expands from the boiling, the liquid in the radiator flows out of the pressure relief port in the cap, and into the coolant reservoir. Once the reservoir is full, coolant will overflow onto the ground.

 

Keeping an eye on this, for I have the same problem. Coolant overflowing from the overflow reservoir. New 'stat, new cap, can't find any leaks, and the oil and coolant look fine. Exhaust smells normal as well. Engine does not overheat. Floorboard is dry. Good heat from the heater. Got a pressure tester on the way.

 

Update on mine, don't know if it will help the OP or not. I had been losing a bit of coolant, and adding some. I think I overfilled the coolant system. My pressure tester came today, and I found the leak almost immediately after the system was under pressure. It was leaking from the radiator hose that goes to the water pump. I tightened the clamp, and it appears to have stopped leaking. I'll keep checking to see if that fixed it, or if I need a new hose.