Boiling coolant?
07-23-2010, 06:51 PM
#1
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Boiling coolant? (this forum is dead)
So I just bought this 1995 A6 for a daily driver. It has an issue with the cooling system and im asking for the old C4 pros to help me out. Here is the deal.
After warm up and driving the car around the temp gauge remains normal but after a while the coolant reservoir cap starts to release steam. Along with the steam there is a decent amount of coolant that is being returned to the tank via the small line located on the top of the reservoir. After the car is shut off the steam stops but you can hear bubbles flowing through the upper radiator hose and up through the overflow line back to the overflow reservoir. The timing belt and water pump have been replaced. I currently am running a coolant cleaner through to remove any blockage or buildup.
Also, when i was draining the old coolant i blew through the upper radiator hose leading into the radiator to remove the excess coolant through the lower radiator hose and it felt sort of blocked.
Does anything have a clue to why bubbles are coming from the engine block through the upper radiator hose while the car is not running?The engine temperature is normal the entire time as well.
All input and questions welcome.
After warm up and driving the car around the temp gauge remains normal but after a while the coolant reservoir cap starts to release steam. Along with the steam there is a decent amount of coolant that is being returned to the tank via the small line located on the top of the reservoir. After the car is shut off the steam stops but you can hear bubbles flowing through the upper radiator hose and up through the overflow line back to the overflow reservoir. The timing belt and water pump have been replaced. I currently am running a coolant cleaner through to remove any blockage or buildup.
Also, when i was draining the old coolant i blew through the upper radiator hose leading into the radiator to remove the excess coolant through the lower radiator hose and it felt sort of blocked.
Does anything have a clue to why bubbles are coming from the engine block through the upper radiator hose while the car is not running?The engine temperature is normal the entire time as well.
All input and questions welcome.
Last edited by r1de23; 08-03-2010 at 02:26 PM.
07-23-2010, 06:59 PM
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Same issue here but the solution is simple for me.
My expansion tank was warped at the filler neck. The plastic had enlarged and the sealing ring wouldn't seat the o-ring properly. What caused it I'm assuming is just a failed o-ring initially and/or the cap not tightened allowing steam to warp the parts.
My car stays at operating temp as well, but without pressure your flow is hampered and it'll boil faster.
check your tank and cap.
k
2002 AR 2.7
My expansion tank was warped at the filler neck. The plastic had enlarged and the sealing ring wouldn't seat the o-ring properly. What caused it I'm assuming is just a failed o-ring initially and/or the cap not tightened allowing steam to warp the parts.
My car stays at operating temp as well, but without pressure your flow is hampered and it'll boil faster.
check your tank and cap.
k
2002 AR 2.7
07-23-2010, 07:29 PM
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Same issue here but the solution is simple for me.
My expansion tank was warped at the filler neck. The plastic had enlarged and the sealing ring wouldn't seat the o-ring properly. What caused it I'm assuming is just a failed o-ring initially and/or the cap not tightened allowing steam to warp the parts.
My car stays at operating temp as well, but without pressure your flow is hampered and it'll boil faster.
check your tank and cap.
k
2002 AR 2.7
My expansion tank was warped at the filler neck. The plastic had enlarged and the sealing ring wouldn't seat the o-ring properly. What caused it I'm assuming is just a failed o-ring initially and/or the cap not tightened allowing steam to warp the parts.
My car stays at operating temp as well, but without pressure your flow is hampered and it'll boil faster.
check your tank and cap.
k
2002 AR 2.7
07-23-2010, 07:31 PM
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For my experience with blown headgaskets i would get an intermix between the coolant and oil or vice versa. The oil and coolant are completely clean... It makes no sense.. could a clogged radiator have anything to do with it? maybe the coolant pump is cavitating a bit and creating bubbles due to lack of flow?
07-23-2010, 11:31 PM
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Once the car has warmed up, check the lower radiator hose to see if it's warm. If it is, then you can start thinking about BHG. But, if it isn't, then I would look at the last time the thermostat was replaced. I had similar symptoms and it was a relatively quick fix with a new OEM Audi thermostat. I recommend only using this type.
If that isn't the solution then it could be the radiator.
If that isn't the solution then it could be the radiator.
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07-24-2010, 09:20 AM
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I'd imagine they are very similar, but I'm only familiar with the C4. You can get to it without taking the timing belt completely off if you are careful. There are instructions somewhere here.
You can buy a tool called a combustion leak tester, or block tester for around $25. This will help tell you if you have a BHG.
Have you verified that your fans are coming on? If they aren't, it could be that the sensor in the bottom of the radiator has failed.
You can buy a tool called a combustion leak tester, or block tester for around $25. This will help tell you if you have a BHG.
Have you verified that your fans are coming on? If they aren't, it could be that the sensor in the bottom of the radiator has failed.
07-24-2010, 09:49 AM
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That could be a good thing since it lowers the chance of BHG. This happened to me one summer after high-speed driving and then stopping. It even overflowed some.
It only happened once. Then a year later I had worse symptoms that were consistent, and I was fortunate that it was the thermostat. You are using the blue coolant?
It only happened once. Then a year later I had worse symptoms that were consistent, and I was fortunate that it was the thermostat. You are using the blue coolant?