SVBurgess

No coolant spilled anywhere else than the tank - I agree that the problem must be caused by over pressure and venting at that point. I’m also quite sceptical too, and I’m obviously not a mechanic, so It would be more than possible that I have misunderstood the most recent diagnosis or am being fed a line! But i’m taking it back in on Thursday (having given it two long motorway runs) to see if the error code that came up is still clear (and to report any further leaks, if they happen!) so I’ll find out the specifics then (of the code and the valve) and post them. Managed a 100+ mile round trip yesterday with no incident, but far too soon to say if anything has really been solved. There have been false dawns before and I’ve already almost resigned myself to a future of regular topping up rather than spending time and money on trial and error repairs!

Have been told there was an electrical fault to the valve on the tank which was preventing correct opening of valve when coolant hot/under pressure. Allegedly now fixed - but I’m still a bit sceptical!

The lid is brand new as well as the tank, so unlikely to be those. Currently being investigated again at the garage that fitted them, so we’ll see 🤞

Despite brand new header tank, the same problem (coolant disappearing from tank after first substantial -100 mile - motorway drive and visible pooling of coolant under tank and spots of coolant around tank) has occured again. No sign of any coolant leaks elsewhere in engine/under vehicle. Coolant - what’s left of it - is clean. As is the oil in the engine. Car ran just a little hotter than usual towards the end of the drive - 101 - 103 C, but did not overheat. Any ideas? This is proving very frustrating - and I seem to have just shelled out for two unnecessary jobs!

Thanks for all advice. Have just had new header tank fitted - hope that this will have solved the problem🤞 (although not entirely confident in the light of the many apparent weaknesses of these coolant systems!)

Yes! Sorry!

My 2014 Octavia TDI SE has been losing coolant. Light came on and was diagnosed by first mechanic as leaking water pump, which was replaced at some expense. Coolant light is still intermittently coming on, with loss of coolant. Two more trips to the mechanic, plus a second opinion. Pressure test revealed no leaks. When the light has come on on a journey and I have had to top up I have found coolant pooling under the expansion tank (see photo). Is this possibly a leak from the tank or from hoses/seals located near. And why has this not showed up on a pressure test? This is now a three week saga and I suspect the water pump replacement might have been unnecessary. Any advice would be gratefully received.