200tdi slow to heat up, any ideas?

Hi,

My 200tdi from a disco (now in my 2door) takes ages to heat up. Sometimes up to temperature within 15 mins if I'm lucky and theres been some hills to get up, usually a fair bit longer..

It was worst than this, but when I did my cambelt 4 months ago, I also changed the thermostat and viscous fan for new ones. It has made some difference but not as much as Id hoped..

Sometimes once its warmed up it even cools back down a fair bit again, untill I reach a hill or something to make it go back up.

Any ideas?

3 choices really.....

1) High temp stat........think they're 90' instead of 82' or something like that
2) Rad muff
3) Electric fan