It has nearly 90000 on the clock and hasn't really been too much trouble over the years. Apart from a steering rack and a starter motor. More recently the turbo went 'pop' which after the repair we thought would mean that we'd be OK again for a few more thousand miles.

But on a local journey yesterday it started juddering and I noticed that the temperature needle was up to the 3/4 mark. I pulled over immediately, lifted the bonnet to cool it down. The temperature seemed to go down pretty quickly so I started off again. But it happened again shortly after, so I stopped again etc. Basically I 'nursed' it to the nearest petrol station where I checked the coolant level which appeared to be low, so I topped it up. But it still needed to be nursed (stop/start) home.

I left it unused overnight to let it really cool down. I have used it again on a very short journey this morning and although it doesn't overheat and judder, because it doesn't have time too, I can tell that it is getting warmer much quicker than it ever used too. So the coolant top up hasn't resolved it.

What could it be?