After selling my car for salvage recently I began to wonder if I could repurpose my next car's engine for anything. Can old car engines be made into generators or other useful machines?
Basically the sky is the limit. If you can dream of something which it can connect to, you could utilize it. There are limits, of course. I mean, you couldn't pull out a 400lb engine and expect to put it in an RC car. If you can devise a way to mount it and attach it to an object which needs power, you can make it happen.
Things which I've seen engines used for outside of cars:
- Airplanes (or other flying things)
- Air boats
- Generators (though, this use is abusive to a car engine due to the constant RPMs needed to run the gennie)
- Larger water pumps
- Tractor engines (replacements when the original has bit the dust - takes some work, but it can be done)
- Other cars
- Chain Saws
- Snow Blowers
- Motor Cycles
To add to Paul's answer - conventional boats are a very common application for old car engines, a good example of this being the 'long-tail' boats found in South-East Asia, which often use them: see This wikipedia page for example...