As suggested in attached Dow SDS triethylene glycol is slightly soluble in heptane. I think that Carbitol or Cellosolve could be than better miscible as they have only one hydroxyl group. The length of the chain (and amount of O atoms) can be also the case for longer PEGs. I think that finally I will just have to check this experimentally for Cellosolve, but thank you for your interest and help.