About that "flushing oil"...... I days gone by, I've had a few cars show up at out shop that had oil pressure issues. The ones I'm referring to came to us after having an OIL CHANGE CHAIN STORE PERFORM A CRANKCASE FLUSH. From my experience, crankcase flushing can turn out VERY BAD.
I say this because heavy internal engine cleaning can be BAD....or worse. I say this because there have been some cars come in with oil pressure problems that had a "crankcase cleaning". When one does this, the process breaks loose internal sludge and this will get circulated throughout the engine. This crankcase debris can and will plug up things like oil pump pick-up screens.....this can cause severe internal damage! I first ran across this issue years ago when there were some oil change stores that started selling this to their customers. Needless to say, this didn't end well and the oil change franchises stopped this practice. I'm pretty sure there were a few ENGINE REPAIR CLAIMS from this flushing process.
The best way to try an INTERNAL CLEANING is by doing several oil changes and filters to loosen and catch this dirty sludge. When we used to run into these dirty crankcases, we did an oil and filter change and ran the engine at moderate speeds. Then shut it down, drained the crankcase and replaced the filter. Then repeated this process 2/3 times doing a filter and new oil each time. YES, it's time consuming... new oil has an excellent detergent action that is not too intense which will not cut thru heavy internal sludge and cause internal oil restrictions.......like a plugged up oil pump screen.....which is just about the same as very low oil pressure. Remember the old days of oil changes every 3000 miles....... this was to eliminate the issues just described.
If one simply does regular oil intervals, this won't happen. BOTTOM line is, do not do a chemical internal flush........ Jake