after fitting the new rad earlier this week and taking the car on a couple of short(ish) runs in order to get it up to temperature, things were looking ok with the temp gauge remaining bang on 90.
i plucked up the courage to take it to work today (a 13 mile motorway commute) and, again, all was well until just before i arrived and the temp crept up quite quickly -on further inspection the bottom hose had disconnected (my fault as i used a cable-tie to secure it).
i resecured the hose, this time with a jub clip, and re-filled the coolant with the bleed valve open.
turned the car over in my lunch break and again it hovered nicely at the 90 mark.
however, on the way home, just after i'd committed myself to the M61, the gauge started to rise and fall quite erratically and then just went up and stayed up. All hoses are still intact and there are no obvious leaks.
Any suggestions as to what has gone wrong: is it worth persevering with or should i just get rid?
thanks in advance
edit: i have done a forum search but cant find a definitive answer to my particular problem