You may see GI upset with ingestion. Small exposures would have mild signs. Worst case scenario would be if the animal vomits or is induced to vomit and aspirates the oil.
With an ingestion, no specific treatment needed. Monitor for stomach upset and respiratory signs if pet vomits.
If your cat got motor oil on it's skin, you should wash it off. Use pet shampoo or dawn dishwashing liquid.
If there is a possibility that you cat may have ingested any antifreeze, however, then it is a different situation entirely and you need to get your cat to a vet ASAP!