I use straight lye to make my own a base for some of the various cleaners I use in pressure washing. I also use citric acid for those things that the lye attacks... like aluminum. 
Many of the chemicals on the market for "hard water stains" and mineral buildup are based on citric acid, as well as those sold for removing mineral buildup from the burner coils on pressure washers. That's what I'm going to try on my radiator when I do it; I'll let y'all know how well (or not) it works.

As for whoever mentioned mixing up lye with warm water, that in a nutshell demonstrates what's wrong with some of these homebrewed DIY "it hasn't killed me yet" kind of posts. Mixing lye with water generates a tremendous amount of heat, depending on ratios and so on, and one of the most common injuries I've heard about with this stuff is people mixing it with warm/hot water, thinking it will make it dissolve better, and then capping the container to shake it up. The container explodes with great force, driving the caustic into every possible orifice, fold, nook and cranny, so now you have thermal burns to go with your chemical burns. I use the coldest water I can get and mix veeerrryyy slowly.

Another variation is pouring the water in on top of the lye while looking down into the container. Bye bye eyeballs. 

I had a guy working with me that cut one of his gloves and didn't tell me about it. A couple of days later he called me to say he had a dime-sized hole in one of his fingers. One of the things about lye is that it can poison you if it works its way down through a burn like that. He was sick for about a week. 

Can't really think of a good use for lye on a Vanagon, particularly one that wouldn't be better served by something else.

Cya,
Robert