Higher order polynomial problem...

Markas

Hello friends, yesterday i faced one problem and i m still searching answer for that, but couldnot. In my simulation i was having material properties at different temperatures. So i thought to define viscosity as a function of temp with help of Polynomial equation which is avalibale in fluent. i used higer order of polynomial(6 order). i found that solution was showing diverging behaviour. After that i took polynomial of lesser order(second order) in that case solutions was moving towards convergence. so why higher order is giving diverging solution?