The coolant level warning had come up on the MFD yesterday, so checked it this morning before going anywhere. Was slightly low in the expansion tank, so i went in to the garage to get some antifreeze (better that than water at this time of year eh.) Unscrewed the lid off the tank and placed on the battery bag, topeed up with anitfreeze, all back together, antifreeze in the boot, just incase it needed any more, then off i went. Pulled up in a car park after traveling 30 miles, and noticed steam coming from the engine bay. not much, just a little. popped the bonnet to have a look and see if i had any leaky hoses or anything. as i was pulling the second bonnet catch, i clicked what i'd done. Lifted the bonnet, and there was the cap, still sitting on top of the battery. Coolant still at the same level too. I wonder if the expansion tank lid had been squeezed between the battery bag and the insulation on the under side of the bonnet. who knows.
What kind of difference would there of been after doing a 30 miles trip with no cap on the tank?