now a diesel head..
AO Silver Member
Join Date: Sep 2014
Location: United Kingdom
sound like you may have found the issue, any early venting will cause the coolant level to drop, on the modern systems it shouldn't cause any other Issues, on some cars the cap failing or bleed screw threads crossing can create a situation where the coolant system is never running at the pressure its designed to, coolant boiling point becomes lower and coolant as vapour squeezes its way past,then to cause further problems air gets sucked in as the system is cooling down...a viscous circle that ends in an overheat.
its worth replacing the cap every now and then just to be sure,some cars have it as a service item at every 50k or so.