CORKY

This is so simple it is going to annoy a LOT of people. Especially those who have spent years - and a fortune - trying to find the cause of MGF/TF overheating. My MGF was overheating after a longish run at speed (say on a motorway) when I left the motorway and sat in slow moving traffic. Steam from the rear vents, bubbling coolant, temp gauge going through the roof! The problem has nothing to do with air-locks, HGF, thermostat failure, blocked radiator, fans failing to come on - or any other obvious answer. The answer is this: If you petrol tank is, let's say, half full at the start of your long journey, then, as you travel you will use a fair amount of fuel. This leaves quite a powerful VACUUM in the fuel tank (have you ever noticed the rush of inward air sometimes when you remove the filler cap?). This vacuum build-up leads to fuel starvation - running lean in other words - and this means the engine, while quite lively in performance, has been running HOT, possibly very HOT if your coolant level is a bit low. This is fine on a motorway when you have loads of airflow and the temp gauge looks fine - but the moment you stop, or join slow moving traffic you have no airflow. The engine has got very hot, and it very quickly gets hotter - because you are STILL RUNNING LEAN. The answer is ultra-simple and of no cost. REMOVE THE (GREEN) INNER SEALANT RING IN THE LOCKABLE FUEL CAP. While this might make the fuel cap very slightly loose, it still locks, and AIR CAN GET IN. But what is better a slightly rattling fuel filler cap or the risk of HGF!!!!!