I think this was an Astra with a similar fault ,only using a lot more coolant than your car , but explains the gist of a faulty cap and how it can be hard to find .
" The one that fools most inexperienced mechanics is the coolant leak caused by the expansion tank cap, the yellow one. I had random coolant leaks and no one could find anything wrong with the car. It was pressure tested at Lookers and kept for a day. Six mechanics and a supervisor couldn't diagnose it. It then went to an independant Vauxhall specialist who pressure tested it and drove it, but couldn't find how the coolant was vanishing! I had a 5 litre container of red coolant and was topping up every few days, sometimes every week. Sometimes the car would scream after driving up hills! Another main dealership, Arnold Clarke, suggested that was caused by the brakes, but there was nothing wrong with them. All this because they couldn't look for an error code. I was shocked by how little some of the mechanics knew. Most have a computer to search on for fixes!
I replaced the cap on the coolant expansion tank and this solved the problem instantly. The rubber seals had gone a bit funny and the small plunger held by a spring under the top of it was lifting - this caused steam to vent through the actual thread. That's why it screamed! "
Hope this helps you .
Posted on Tuesday 11th of January 2011Don't understand this? Ask a question