I recently bought an immaculate 2000W Passat Estate with the 1.9 115bhp TDI PD engine. It came with a full dealer history and 94,000miles. I can't find fault with it other than when checking the fluid levels last weekend I noticed the coolant expansion tank was close to the min mark. I duly topped it up to MAX with a 'red' antifreeze mixed 50/50 as per the manual. Checking again two days and about 50 miles later and its well on its way back towards the minimum mark. There is no sign of oil in the reservoir or water on the dipstick, mayo on the oil cap. No water has leaked onto the concrete where I park at work. The exhaust output is fine. I have heard a gurgling noise from within the dash and heater area when starting from cold in the mornings. Are there any common water loss faults with these cars? Where do you suggest I investigate next to find the fault?