A slow, mysterious coolant loss with no puddle under the car — and a sweet smell after a drive — is, on a lot of VWs, a cracked plastic coolant flange or connector. That's the plastic elbows and temperature-sensor housings VW dots around the head and block. They go brittle with heat and age and split at a seam or an O-ring, and because they hide low and behind things, you won't see it until the level drops
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