96 Z28, 80k miles, water pump and opti replaced in 2005 (mileage unknown).

To make a long story short...
An idiot mechanic improperly installed the coolant level sensor causing it to fly off the day after leaving the shop. The car left a mile long trail of coolant down a major road and completely soaked the passenger side of the engine bay. The car was overheating, I didn't catch it and kill the engine until the temps had already climbed above the red zone (it was dark and the bulb behind the gauge is burnt out, aren't I lucky). I found the problem and reinstalled the sensor correctly. I saw the downtime as a great opportunity to install my Pacesetter LT's and Magnaflow.

I think I might have a blown head gasket... Or am I just paranoid?

Pro-Blown Gasket Theory:

• Car frequently overheats. Thermostat and coolant temperature sensors (2) have been replaced. The cooling system has been filled and bled (radiator topped off cold, idled until warm, filled again and bled at 2 screws, then sealed). There are bubbles coming out of the radiator even when the car is warm. I've bypassed the throttle body so I can see bubbles emerging in the radiator from the hose that connects to the metal line on the back of the passenger side head (runs along valve cover).
• Substantial amount of water pooling in tail pipes (around 1/4 cup). Dripping from junction of exhaust system tubing. Occasional white smoke (not at all thick, very faint).

Con-Blown Gasket Theory:

• Oil level hasn't increased (I'd assume there's no coolant leaking into the oil system or down the cylinder walls). Haven't checked the oil's consistency, will do soon.
• Have I bled my cooling system properly? Could that be a cause of the surfacing air bubbles? The bubbles come in waves at all temperatures.
• Condensation? It's been raining pretty heavily in my area this past week. Would this explain the dripping? The system is not welded and is held together with the supplied band clamps. White smoke comes and goes, could this been steam from condensation? Also, the smoke is very faint.
• Waves of bubbles or white smoke/steam don't match combustion cycles... are more intermittent.

I'm thinking I have a small leak between a coolant passage and cylinder. Could a piston could be forcing air into my cooling system causing the bubbles? Wouldn't there be a large amount of smoke?

 

have you pressure tested the coolant system to see if you have any other leaks?

 

Just wondering, when you bled the cooling system was the nose up in the air? If not Id get the nose in the air and try bleeding again.

.02

 

No, but I might rent one. Would using a compression tester for the cylinders have the same effect? I'm guessing it would, my father has one from his mechanic days but I don't think it's been used since 1980. Hopefully it still works. As far as other leaks go, I don't appear to be loosing much coolant... then again, I can't really say.

Nope, but I'm going to bleed it again today on ramps. I'm also going to run a friend's 95 Z28 alongside for reference, I don't ever recall seeing bubbles from the radiator while running with the cap off. How fast does the coolant circulate through the system when warm? Should it stop bubbling after some point?

I'm just trying to uncover any possible problems before they escalate... that's if they even exist. It doesn't sound like that much of a stretch, especially after the whole overheating episode. I'd just rather not turn my power plant into an industrial looking furniture set.

 

I lost the head gaskets on my engine not to long ago and the only sign was white smoke on warm start up. Ran just fine other then that. Never did the white smoke again after it was started and run for 30 seconds but you could smell the unmistakable smell of coolant at the rear of the car around the exhaust and it did have an increased amount of condensation in the exhaust system. Never over heated either. When I pulled the heads off the combustion rings on the gaskets were fine but the material around them had failed on the rear 2 cylinders. The pistons were nice and steam cleaned. I would run the tests mentioned above and then make the determination but if it's over heating it's either an air pocket due to clogged rear steam pipe or blown head gasket. Since you see air coming from that tube that would leave me to believe that it's not clogged but if you keep getting air its more then likely a blown head gasket. Pulling your spark plugs can give you a real good idea if the engine is injesting coolant as it leaves tell tail signs on the plugs.

 

pull the drain plug.. if water comes out first then you will know for sure.

 

If it got that hot...stuck in the red; very good probability head gasket is blown. Same thing happened in my car when a radiator tank busted years ago; overheated and it was done.

 

Make sure you don't have the 2 small hoses that connect to the radiator by the cap installed wrong. They are just below the cap. If you install them backwards the car will push coolant out and then overheat within 15 minutes of running. shbox has a diagram.

 

As the car was running fine & good before it was overheated, I doubt any lines were installed incorrectly.

Catmaigne, you don't say if your coolant level is dropping. Do you fill it then after some driving, it's dropped? You say there's no oil level change but it's coming out the exhaust.

Sorry buddy, you have a blown head gasket. Probably between cylinders 5 & 7, notorious on SBC's.

Pull them heads! I suggest you send them to the nice folks at http://www.advancedinduction.com/ for some working over-along with your intake.

 

The oil level has dropped 2 markers on the dipstick. Last oil change was 30~ miles ago (right after the header install), everything should be settled. This isn't looking too good.

I'm going to pull a quart or two from the pan to see what it's like and check for any leaks (mainly dipstick).

 

When bypassing the throttle body I attached the 2nd hose down from the cap to the steam line that runs along the passenger side valve cover. I followed the directions on shbox and unplugged the hose on the driver's side of the TB and plugged it into the steam line after undoing the rubber elbow that feeds into the passenger side of the TB. I never touched the reservoir hose at the top of the radiator.

 

I drained about a quart of oil into an empty 2 liter soda bottle. There was no coolant settled at the bottom or anything in the container other than the black 5w30 I put in 2 or 3 weeks ago. Disregard the post about oil level above, I'm unsure of the level when I filled her up. I may have confused it with the Firebird I filled yesterday.

I have a new theory on what's causing the bubbles and I think my gasket might be fine. A friend of mine told me that bubbles were only coming out of the 2nd hose down from the top of the radiator, or the line that should hook into the driver's side of the throttle body. Being that my throttle body has been bypassed, that hose has been hooked into the metal coolant line that runs along the passenger side valve cover and into the back of each head (the bypass looks like the diagram joelster posted above, whereas a stock Z28 would have lines leading into and out of the throttle body between #3 and #6). From what I've read, that metal tube is called a "steam line." I'm guessing this line is filled with boiled coolant vapor that's supposed to travel into the throttle body so it can be cooled and condensed back into liquid. Assuming my friend isn't lying and my theory isn't crap, I'm getting bubbles in the radiator because my throttle body isn't there to cool the vapor from the heads, causing bubbles and steam from the radiator and not a blown head gasket. Am I right?

Has anyone with the throttle body bypass ever experienced this? I can't say if there were steam or bubbles coming from the radiator before the episode I had because the car never used to overheat. I've been reluctant to drive the car since I've suspected the head gasket, but I can't say if it still gets hot after installing the new thermo and sensors.

As for the light periodic smoke and substantial water from the tailpipes, I think condensation could be to blame. It's been a pretty rainy week and the car wasn't started often. My tailpipes are also angled so that rain could flow into them easily.

 

Nope, your theory is crap...the TB does not "cool vapor from the heads"....I've never had any issue since the TB coolant bypass mod on my car.

 

IMO the reason why you are getting bubbles into the radiator from the return line is because the cooling system has not been properly bled and there is still air in the cylinder head passage ways. When the system has been bled right you will get a constant flow of coolant out of that line. Have a friend stay in the car constantly monitoring the temp gauge. Start engine and watch radiator for several minutes to see if bubbles go away.
If you really want to make sure your head gasket is fine, get a pressure tester, take the spark plugs out of the block, apply pressure to system, watch gauge, if gauge goes down quickly then take pressure off and rotate engine to see if coolant makes its way out of a spark plug hole. Also, if it were indeed a gasket that gave way to a coolant passage the cooling system would build pressure immediately upon start up.

 

X2
You really need to start using some of the tools described in this thread to find out if it's a bad head gasket or air in the system or you can keep driving it and risk cracking the head. These things can take a long time to bleed correctly. It took me 20 min with the nose way in the air to do it one time before I cleaned the crossover tube and banjo nuts. they get a ton of build up on them after some years and the passages get smaller and smaller. Sometimes they get clogged solid.