Will a French Drain on the outside of a house keep water out of a crawlspace?
Cinder blocks are quite porous. To keep a basement or crawl space dry means keeping subterranean water (water table) and surface water off the foundation wall. 

Where I live we have a water table at about -24". The only way we can keep basements or crawl spaces dry is to: 1) install a 4"-6" perf pipe about 6"-8" BELOW the basement slab or crawl space, 2) encapsulate the pipe in drainrock (round 3" minus rock without fines), 3) extending the drainrock to within 6" or so of the ground surface so any water trying to "build-up" against the wall, will be drained down to the perp pipe and carried away, and 4) waterproof (coat) the foundation wall to keep surface water from penetrating the wall. 

Sometimes we'll wrap the drainrock with filter fabric, depending on the soil. Make sure the perf pipe extends to a drainage swale and we don't connect roof drains into the perf pipe...we extend the roof drains (in a solid pipe) to a drainage swale too. We also add a 1/2" protection board (inert cement board) on top of the wall coating, so when the drainrocks are dumped in, they don't damage the coating. 

This system works, unless you are located next to a large hill where the water table "up the mountain" can "push" pressure on the water table under your house. Then, it will cause the water table to rise UNDER the house. To fix this, we run french drains about 10' on center under the house...very expensive.