Originally Posted By: bob_ninja
I can see how flushes done at reglar intervals should keep an engine clean at almost no risk.
I disagree about the no risk part, if you're using the typical engine flush which uses kerosene or a similar type of solvent. What happens after you've finished the flush and you drain the oil? There is going to be some residual solvent left behind, and that's going to contaminate the next oil that you put into the engine.
If you buy a car new and do not push your oil changes beyond their reasonable limits, I do not think an engine needs to be flushed at any point in it's life. (the sludge prone engines like the old Toyota V6s are an obvious exception-although one could argue that they only sludge up when you've pushed the oil beyond it's "reasonable limit" for that particular application, so my previous statement would still be valid)