I have a few suggestions on this since it's in the area of my work.

 

Steve is correct about the two layers remaining after the hexyl alcohol and acetic acid reaction is complete.  However, in my experience, that type of esterification can be exceedingly slow and even though you think it's complete, you can come back 24 hours later and find it clouding up again, meaning more esterification is taking place and you're producing more water as a by-product.  If that's the case, then your distillation is really working properly and it's distilling off more water, produced even faster because you're heating it again,  and even traces of it that you can't necessarily see a lot of condensation from may be coming off.  

 

The fact that your temp then drops to 80°C happens frequently in our lab.  It generally means your apparatus is losing heat more rapidly than your poor hot plate can put out.  We can sometimes (not always!) remedy that by insulating the apparatus as much as possible with towels - make sure they're heat resistant and fireproof!

 

Sometimes labwork is more art than science!

 

-Norman