Since my last post I have been using the ZT, mostly on "econ" setting but occasionally with AC on and I have no more "white stuff" appearing. I think maybe this was partly because the system was overfilled (garage not me)! Another factor maybe the fact that the upper bleed hole in the header tank does in fact produce some coolant flow. I have done the header tank cap off from cold observation and this showed the lower hole showing a dribble of coolant after 3mins which with stops and starts increased to a good flow by 6mins. whilst this was happening I could see a flow of coolant from the upper hole, just visible on the lower edge of the tanks neck. I had poked around in this hole with some soft wire prior to this. The over filling was not too bad but was over the internal fins. I'm intrigued to know what goes on with the filler cap on, I am wondering if when the coolant level closes the bottom of the header tank neck and blocks the lower hole if the coolant is then diverted into the upper hole and thence into one of those slots/apertures in the filler cap? Maybe nonsense but I am puzzled, that cap seems complicated and surely there must be reason for that. The trouble is you never know what previous owners/garages have done. Chris.S
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