Pusb

Hi all,

I don't post here often, but the observant of you will remember that I posted on here a year ago after my MG had overheated on the motorway.

I never completely found out why it did that, but the only explanation that I've been given by my mechanic is it was likely to have been a dodgy expansion tank cap. I replaced it with the genuine black cap.

Anyway, since then I've been keeping a very close eye on the cooling system. One thing that kept happening was a build up of air in the radiator.

I had to have the Cambelt changed over the winter so at the time I asked my mechanic to check the cooling system over. I asked him if he thought it was the HG (thinking that if it is I could save a bit by having it done at the same time as the cambelt), and he said no. Unfortunately his in depth investigation was to take a look at the oil and coolant and to conclude that the HG was fine because both of them looked clean. His words been that the HG usually doesn't fail in any other way but between oil and coolant.

Anyway, I've thought that I can't be scared to drive the car, so I have been using it during the nice weather. Around town even in the heat its been fine. Once a week I would open the bleed screws and a little air would come out.
However last week I needed to do a 240 mile round journey. A risk I know but I thought this would be a good test. So out leg of the journey (120 miles) car drove fine, got to my destination and I checked the expansion tank. The coolant had raised a little and when cool I opened the bleed screw and a fair bit of air come out but not a massive amount.
Did the return journey, again the car drove fine on the 120 miles back. However when I got home I checked the expansion tank and the coolant level had risen from half the tank to literally filling the whole tank. I waited until the next day and checked again but sure enough it was still full. It was so full that when I opened the cap the coolant shot out of the tank with some force (keep in mind it was stone cold).

I opened the bleed valves and it was like letting down a tyre with the amount of air in there.

So for that much air pressure to be in the system after just 120 mile journey, can it be anything else other than HGF?