I agree with the above statements,
If a customer bought a jet engine into work with a
problem, excessive oil consumption for example, we would not just top up the oil and take the engine for a run, we would try to find the cause first, and use a function test as a last resort. This is the same with a car, you dont just top it up, without finding out why it was low. Yes I know some people forget to check oil, but not everyone does, so you would expect them to ask when you last topped it up before adding oil.
IMO its not an acceptable way of running things regardless of what underlying issues there may have been with the car, or how it was brought to them.
Also, to put a rod through the block, you would have to be giving it some abuse, otherwise it would have bent/snapped and stopped dead.