Leaderboard

Yeah, like @Rich says, almost certainly the temp sensor. Buy genuine VW for this. I honestly cannot believe that VW never did a recall for temp sensors. Every, and I mean EVERY single vdub model from about 1998 to 2007 has had it's temp sensor changed. There's even a you tube video somewhere of a garage in the US that collected every faulty one it had changed in a big bin. It was full. Thousands. Mk4's, Boras, Lupos, Polos, Phaetons etc and the Audis, Skodas and Seats too. The cause I think, is that the Luxembourg company that made (and still makes them), used the wrong potting compound. The stuff they used set rock hard to encapsulate the two thermistors (One for the ECU the other for the dash). Only trouble is that the physical expansion of the thermistor material is different to the compound, resulting is heat expansion fatigue stress, then failure. Silicone or polyurethane compound (softer) would have been fine, but perhaps not as tough.

Green temp sensor, buy oem. Collecting gtis is fun. Do it.