Short back story -- had a cooling problem I traced back to an air bubble issue, which was caused by a defective radiator cap. I replaced the cap, bled the air out of the cooling system, and everything was fine for about a month. Now the air bubbles are back. I am not losing any coolant, but air is somehow getting into the system. Also, my overflow tank seems to be filling up with coolant. What could be the problem, and what should I do?

 

what kind of rad cap are you using ?, there seems to be one brand that is notoriously bad, sounds like the current cap might be bad as well ? How can you tell that you are getting air back into the system ?. Do you get good heat out of the heater system ?.

 

No heat coming out unless I get the revs up. I don't want to waste a bunch of time and space going through all the symptoms, but I know there is air in the system. I replaced the cap with an $8 cap I bought at Advance Auto Parts, so maybe that cap went bad, but that seems like a weird coincidence. Then again, an $8 part breaking is not that weird.

I will test the cap, but I didn't know if it was normal to get air in the system from time to time, or if maybe I just missed some air when I burped the system a month ago that is just starting to cause problems now, or what else could be going on.

 

you should check your coolent lines, check for any cracks in the lines or
any bad lines with loose seals.

 

if your overflow is filling with fluid, it could be one of two things:

1) overheating causing the fluid to expand -> go into your tank (more than normal)
2) fluid NOT being sucked back through the line because you have a leak on the line from the radiator to the overflow.

 

not burping the system properly is very common on these boards and leads to continual issues with air in the system. Inconsistent heat is a sign of air in the system, so no need to explain any further. A bad rad cap can cause the issues with your overflow tank, but you should keep burping the system until you get consistent heat from the heater.

Idle the car until 3 bars on the temp guage, do not touch the throttle at all, shut it down and open up the bleed bolt on the manifold to allow air to escape and no more bubbles in fluid. Once the car is fully cooled down open the rad cap and see if the rad accepts more fluid, fill it up to base of the neck and reinstall cap. Repeat if necessary. I did this on a recent replacement of the rad hoses and a Mishimoto radiator and it worked for me. Some people suggest lifting up the front end so the rad is the highest point in the system. I didn't have to do that but it might help too. Make sure the heater dial is on hot every time you burp it.

 

Thanks for the replies. I know how to burp the cooling system, I found some threads on it a while ago. Either I'm just not getting all the air out, or there is a leak somewhere. I'm inclined to think the latter, because of the fact that the coolant level in my overflow tank is steadily increasing since the air bubble problem started again. I will have to check the line, the radiator cap, and the radiator neck for leaks.