The Whole Heliosphere Interval (WHI), comprising March 20–April 16, 2008 (DOY 80–107), is a single Carrington Rotation (2068) designated for intense study through observations and simulations. We used solar wind data from the WHI to run the Coupled Magnetosphere–Ionosphere–Thermosphere (CMIT) and stand-alone Lyon–Fedder–Mobarry (LFM) models. The LFM model was also run with the WHI solar wind plasma parameters but with zero interplanetary magnetic field (IMF). With no IMF, we expect that the cross-polar cap potential (CPCP) is due entirely to the viscous interaction. Comparing the LFM runs with and without the IMF, we found that during strong driving with southward IMF B z , the viscous potential could be a significant fraction of the total CPCP. During times of northward IMF B z , the CPCP was generally lower than the CPCP value from the IMF=0 run. LFM tends to produce high polar cap potentials, but by using the Bruntz et al. (2012) viscous potential formula (Φ V =μn 0.439 V 1.33 , where μ=0.00431) and the IMF=0 LFM run, we calculated a scaling factor γ=1.54, which can be used to scale the LFM CPCP during the WHI down to realistic values. The Newell et al. (2008) viscous merging term can similarly be used to predict the viscous potential using the formula: Φ V =νn 1/2 V 2 , where the value ν=6.39×10 −5 was also found using the zero IMF run. Both formulas were found to perform better when V (solar wind)=V x , rather than V total , yielding similar, accurate predictions of the LFM viscous potential, with R 2 >0.91 for both formulas. The γ factor was also used to scale down the LFM CPCP from the full solar wind run, with most of the resultant values matching the CPCP from the Weimer05 model well, even though γ was derived independent of the Weimer05 model or the full LFM data. We interpret this to be an indication that the conductivity model in LFM is producing values that are too low, thus elevating the CPCP values.