  We investigate the effects of viscosity terms depending on the Hubble
parameter and its derivatives in the dark energy equation of state. Such terms
are possible if dark energy is a fictitious fluid originating from corrections
to the Einstein general relativity as is the case for some braneworld inspired
models or fourth order gravity. We consider two classes of models whose
singularities in the early and late time universe have been studied by testing
the models against the dimensionless coordinate distance to Type Ia Supernovae
and radio-galaxies also including priors on the shift and the acoustic peak
parameters. It turns out that both models are able to explain the observed
cosmic speed up without the need of phantom (w < -1) dark energy.
