If he watched what he was doing instead of looking at the camera, more of his water would go into the radiator and less on the ground. Also, the photographer seems not to have wound the film all the way to the next blank piece, since there's a partial double exposure.
What is he using to fill with, looks like a skull.
Might be a gourd. If so, he could saw the end off the stem and pour through that with less spillage.
Can anyone make out the plate? It would be fun to know where and when. Pretty sure it's a gourd he's using.
Kentucky, but year?
If he had the License plate below the crank, it would have allowed for better air flow and cooling! Then maybe he would not have to add water.