Engine flushing can be dangerous if the engine is especially "gunked" or
varnished up. If the flush breaks loose some large chunks of "gunk"
(carbon, varnish, dirt etc.), this gunk ball can clog an oil galley,
most likely only momentarily. However it doesn't take but a very few
seconds of oil starvation to a main bearing to score or ruin it. 
I highly recommend Marvel Mystery Oil as a cleaning additive. You can
just keep driving and changing oil at your normal interval w/this truly
time tested produce.
Mark B. Magee
87GL 83K
Kemah TX