Expansion tank!!! Help help!

[rd070707]

I had this same problem for over a year now, car runs at normal temp 79/80 at driving and will slowly rise to 90 if in traffic for a good while. I think in 8 months I had to top the coolant up once as I was getting some overflow too.

I have tried new caps but to no avail. Unless I could try a new header tank too but I had a sniff test done and all was clear car starts and drives perfect.