Russian fudge analogy applies here.
Two ways to cook russian fudge.
One is to cook the fudge while stirring it constantly, this means that the bottom never gets burnt by the hot pan.
The second way to cook the fudge is to not stir it at all, and just eat the top part that isnt burnt, and leave the burnt bottom part in the pan.
However if you start stirring the fudge half way through, you mix burnt bits through the whole thing, and none of it is edible.
In my experience this applies rather well with oily gunked up engines, old coolant lines etc, etc etc.
For example, I had a perfectly good water pump, till I ran a coolant flush, which then seemed to dissolve all of the dirt holding it together. I now had a waterpump which pissed water out, every which way.
Same with a mate who hadnt done an oil change for about a year and a half.... (lol) His engine died the day after he changed the oil, blocked all of the oil galleries to the head by stirring up all of the old crap in the motor. (Yes, it was an SR motor
)