I've read anecdotal accounts here and there that cleaning various parts of older engines can cause various parts to fail, or be pushed over the edge.
Basically, people say that as the engine ages and wears down, the built up "crud" of various sorts kind of fills in the wear gaps and keeps things functioning, but that cleaning can both release so much gunk that it clogs things up, and loosens worn parts of making things fail.
I've heard this about just about everything that can be cleaned without taking the engine apart, the air intake, the pistons and valves, the crank case and the cooling system.
In my case I've got an older vehicle ( 97 Mazda 323 ) which I've visually verified is extremely dirty in just about every possible way. There is think oily sludge in the intake manifold, think carbon buildup in the crank case under the valve cover, and heavy rust in the cooling system.
I'm worried that if I start cleaning things out things might start breaking as a result.
Is this something I need to worry about, and if so are there any precautions I should take, or is this really just an urban legend?
Here is an example of one anecdote I've read regarding flushing the cooling system for example:
Search under my name...Ive done the citrus flush twice and both times other components have been taken out, like the radiator, water pump etc. Im not saying dont do it, just be ready - anything that is on the edge of failure will be pushed over. Have your credit card warmed up and parts supplier ready forewarned :-)
In my opinion, if your cooling system is functioning properly, I would not do the citrus flush.