Mysterious Coolant Loss in Audi S1 Without Visible Leaks

Having some experience with Audi models, I faced a similar issue with my 2015 Audi S3. The coolant reservoir also showed decreasing levels without visible leaks on the ground. After noticing this, I first checked all visible connections around the engine but found nothing obvious. The workshop performed a pressure test on the cooling system and discovered that the issue was related to a faulty wiring connection to the coolant level sensor. The connection had corroded over time, leading to incorrect readings. The repair involved replacing the wiring harness and connector to the sensor, which cost 95 Euro including labor. Since the fix, the coolant level has remained stable and the check engine light has stayed off. Before jumping to conclusions about head gasket issues, its worth checking the simpler potential causes first. Could you share: Any specific error codes you received? Does your engine show signs of overheating? Have you noticed any white smoke from the exhaust? When was your last radiator fluid change? This information would help determine if your issue matches what I experienced or if it points to something different.

Having some experience with Audi models, I faced a similar issue with my 2015 Audi S3. The coolant reservoir also showed decreasing levels without visible leaks on the ground. After noticing this, I first checked all visible connections around the engine but found nothing obvious. The workshop performed a pressure test on the cooling system and discovered that the issue was related to a faulty wiring connection to the coolant level sensor. The connection had corroded over time, leading to incorrect readings. The repair involved replacing the wiring harness and connector to the sensor, which cost 95 Euro including labor. Since the fix, the coolant level has remained stable and the check engine light has stayed off. Before jumping to conclusions about head gasket issues, its worth checking the simpler potential causes first. Could you share: Any specific error codes you received? Does your engine show signs of overheating? Have you noticed any white smoke from the exhaust? When was your last radiator fluid change? This information would help determine if your issue matches what I experienced or if it points to something different.

Last service was just 2000km ago, and they checked the error codes which showed P0217 and P2181. Since my initial post, I also noticed a faint sweet smell near the engine bay during warm-up. The engine temperature gauge stays normal, and I have not seen any white smoke from the exhaust. The coolant reservoir keeps dropping slowly, requiring a top-up every few weeks. The radiator fluid was changed during the service, but air pockets might have formed since I keep having to add more coolant. Engine overheating is not an issue yet, but I am concerned about potential internal leaks that are not visible externally.

Last service was just 2000km ago, and they checked the error codes which showed P0217 and P2181. Since my initial post, I also noticed a faint sweet smell near the engine bay during warm-up. The engine temperature gauge stays normal, and I have not seen any white smoke from the exhaust. The coolant reservoir keeps dropping slowly, requiring a top-up every few weeks. The radiator fluid was changed during the service, but air pockets might have formed since I keep having to add more coolant. Engine overheating is not an issue yet, but I am concerned about potential internal leaks that are not visible externally.

Thanks for providing those additional details. The error codes P0217 and P2181 both relate to engine cooling system issues, which aligns with my experience on the S3. That sweet smell you mentioned near the engine bay is particularly interesting, I had that too before discovering my real issue. In my case, it turned out the cooling fan was drawing air through a hairline crack in the radiator, causing that sweet coolant smell during warm-up. The constant need for coolant top-ups combined with those specific error codes suggests you might be dealing with either: 1. Air pockets in the system that formed after the recent service 2. A small internal leak, possibly from the radiator cap not sealing properly 3. A failing water pump that is not circulating radiator fluid effectively Before spending money at a workshop, try this: with a cold engine, carefully remove and inspect the radiator cap for any damage to the seal. Also check if the spring has proper tension. A faulty cap can cause both pressure loss and air pockets to form. Since you are not experiencing engine overheating yet, this suggests the issue is still in early stages. Would recommend getting a pressure test done soon though, that ultimately revealed the crack in my radiator.

Thanks for providing those additional details. The error codes P0217 and P2181 both relate to engine cooling system issues, which aligns with my experience on the S3. That sweet smell you mentioned near the engine bay is particularly interesting, I had that too before discovering my real issue. In my case, it turned out the cooling fan was drawing air through a hairline crack in the radiator, causing that sweet coolant smell during warm-up. The constant need for coolant top-ups combined with those specific error codes suggests you might be dealing with either: 1. Air pockets in the system that formed after the recent service 2. A small internal leak, possibly from the radiator cap not sealing properly 3. A failing water pump that is not circulating radiator fluid effectively Before spending money at a workshop, try this: with a cold engine, carefully remove and inspect the radiator cap for any damage to the seal. Also check if the spring has proper tension. A faulty cap can cause both pressure loss and air pockets to form. Since you are not experiencing engine overheating yet, this suggests the issue is still in early stages. Would recommend getting a pressure test done soon though, that ultimately revealed the crack in my radiator.

That makes sense about the pressure test recommendation. I will have the radiator cap checked first since its the easiest fix. The sweet smell does worry me though, and since I keep losing coolant, I will book a workshop appointment for next week. Not worth risking engine damage by waiting too long. The lack of white smoke and normal temperature readings are encouraging signs that this might not be a head gasket issue. I will have them check the water pump and all radiator hoses during the pressure test since everything was fine during the recent service. Thanks for sharing your experience, will update once I know what caused my coolant loss. If its just air pockets or a bad radiator cap that would be the best case scenario. Better to catch these things early before they lead to engine overheating or more serious problems.

That makes sense about the pressure test recommendation. I will have the radiator cap checked first since its the easiest fix. The sweet smell does worry me though, and since I keep losing coolant, I will book a workshop appointment for next week. Not worth risking engine damage by waiting too long. The lack of white smoke and normal temperature readings are encouraging signs that this might not be a head gasket issue. I will have them check the water pump and all radiator hoses during the pressure test since everything was fine during the recent service. Thanks for sharing your experience, will update once I know what caused my coolant loss. If its just air pockets or a bad radiator cap that would be the best case scenario. Better to catch these things early before they lead to engine overheating or more serious problems.