Linear instability of shear thinning pressure driven channel flow.

•The instability of channel flow of a shear-thinning viscoelastic fluid is studied in several constitutive models.•Instability is observed in all studied models for a sufficiently high degree of shear thinning.•A general functional form is found to predict the onset of instability in each model.•The study demonstrates that underlying model dynamics play a large role in determining instability.