In the documentary Pump it is stated that Henry Ford initially envisioned his automobiles running on alcohol similar to the ethanol fuel offered at some stations today, but when John D. Rockefeller found out about this and saw the threat it could pose to his oil interests he quietly invested a great deal of money to support the introduction of legislation prohibiting alcohol and was largely responsible for making it law.
How much (if any) truth is there to this claim?
This is pretty much false on nearly all counts. (except perhaps that the Model T's carburetor could run on ethanol which I am unsure if true or not)
Firstly, the timeline is wrong. Petroleum products were a fuel for lamps before they were fuels for cars. Standard Oil products would have competed against ethanol in lamps for decades before they could have competed as fuel in automobiles. By 1908 when model Ts began rolling, gasoline was already becoming a fuel of choice for cars. Prohibition had no role in this choice which was purely about economics (oil was very cheap then) and engineering.
Secondly John D. Rockefeller's views on alcohol were rooted in his family background. His father was absent and grandfather an alcoholic, while his mother was very religious, and she imparted her views to her son. John D. Rockefeller was a lifelong teetotaler and member of the Baptist church (which supported the Temperance movement.)
Thirdly, Rockefeller's financial contributions to the Temperence movement were rather modest in comparision to his wealth and the income of the movement. He was conscious of his reputation as a "Robber Baron" and did not wish to give Temperance organizations like the WTCU the appearance of an organization dependent on his wealth.
The source for most of this is Ron Chernow's biography of Rockefeller.
You might be interested in [this post] (http://www.reddit.com/r/AskHistorians/comments/35h8uz/henry_fords_model_t_could_run_on_gasoline_andor/]) from a few weeks ago, regarding the same question.