I have a couple of questions about these bubbles that I'm hearing so much about. I wrote a post a couple of days ago that we just had a head gasket replaced on our '98 Forester and a few days later we had the check engine light come on and the overflow tank had only about a half inch of collant in the bottom. We tried topping it up with cooland today, ran it and initially there were a few bubbles in the tank but it slowed to about 1 every minute.....does this mean it's time to have the gasket job done all over again or is it possible that it's just air in the system?

No, there is probably still some air in the block somewhere and it is slowly getting displaced by water. The thing that usually is a sign of a blown head gasket is when those air bubbles are filled with smoke or they create an oil sheen on the water in the filler.

Yeah, some bubbling is normal after the coolant system has been opened. If the level in the overflow tank is low after a drive, then I doubt you have a headgasket problem - the bottle would more likely be full to the brim.

 

 

Search for "coolant replacement" on this site, I have shared my best method for having as little air as possible.

I've tried everything possible to remove air from my cooling system, blipping the throttle with the front of car up on ramps while using one of those Lisle "Spill-Free Radiator Funnel Kits" and burping the top hose till no more air comes out.

 

I still get the bubbles tho. What worries me is the black scum/flakes (carbon?). Not seeing any oil, but I'm concerned that it might be a gasket.

 

I get the bubbles on my other roo, but no carbon.

So what you're saying is that if you have a nearly full coolant overflow tank after a drive, then thats indicative of headgasket problems? My Legacys tank has lately been above normal levels after driving... :-\

If the level is too high to begin with then it will be high when it is hot.

 

To check for headgasket problems I would have a block done. It is not very expensive to do.

all by themselves of head gasket trouble. First of all the coolant level will go up a bit when warm normally as it expands. This is why most coolant tanks have hot and cold on them.

Check it the same way all the time and you will get an idea how much yours should change while normal. You can also have a little scum show up and not have a gasket about to pop. There can be all kinds of ugly chemical reactions in an old motor if it has had different kinks of antifreeze.

All cars are not equal. If you are running a very hot thermostat and your radiator is old and not as effective as new you are borderline on boiling.

When the water expands inside your radiator it will be forced into the coolant recovery tank. If it is borderline under pressure it can boil when it hits the open air causeing bubbles. Then if it cools down and sucks back in things are fine.

But if you overheat and have a steady stream of bubbles or if you get that thick brown goo...watch out.

By overheat I mean the engine boils over, not the gauge goes up in heavy useage. The guage should go up a bit in heavy use on an old engine.

Good info here;

http://www.troubleshooters.com/tpromag/200005/200005.htm

 

I had the black-brown goo forming inside my recovery tank that Cookie describes. My engine never boiled over that I know of (I had just bought it used), it just "puked" coolant out of my recovery tank and my temp gauge spiked. I couldn't detect the smell of exhaust, but had the bubbles after an extended drive.

When your coolant goes thro a number of heating and cooling cycles the bubbles will stop.

Jude

Thanks for all you help......my mind is a little more at ease right now!!

1990Legacy: No, a full overflow tank, that is bubbling is a symptom of HG problems. Check the level when cold, and note how much it rises when the engine is warm. The cold level in the morning should be fairly steady. If it's dropping, you have a problem. Maybe HG.

 

Clutchbob: Classic HG problem. There is a tiny leak of compression and exhaust gas into the coolant system.

Would something like that also cause the "Check Engine" light to come on while the car is running?

Coolant in the exhaust could cause the O2 sensor to send out a code.