For cars you can get a flushing additive eg Wynns Oil Flush ,
WYNN'S ENGINE FLUSH PRODUCT DESCRIPTION
The Wynn's Engine Flush Flush is a highly concentrated detergent, designed to clean all oil lubricating systems prior to an oil change. It quickly and efficiently dissolves varnish, sludge and other contaminants from vital engine parts and prevents contamination of fresh oil by residues left behind.
FEATURES & BENEFITS OF WYNN'S ENGINE FLUSH
Cleans engines, hydraulic systems, gearboxes and differentials internally
Quickly and efficiently dissolves varnish, sludge and other contaminants from vital engine parts
Prevents contamination of fresh oil by residues left behind
Frees sticking internal engine components by dissolving deposits
Provides extra protection during the treatment
Quietens noisy hydraulic valve lifters by removing deposits
Is compatible with all mineral, synthetic, single and multigrade oils
Recommended for all petrol & diesel engines
However, I have never used it.
I have known some use this stuff with seriously **** results & at least one new engine.
Lube oils have moved on light years and have super super sexy additive packs.
There is NO requirement for flushing oils, as modern lubes do a fantastic job at holding dangerous contaminants in suspension, particulary at Mickey Mouse marine lube oil drains. Additive pack barely breaks out into a sweat before being dumped.
Remember the engine manufacturer knows best, RTFM. Just spend on purchasing decent branded lube which meets the correct approval.
U.S EPA branded lube additives, flushing oils as expensive fraud (mainly kero based). However the additive manufacturers make huge profits and have correspondingly large marketing budgets.
Keep life simple by doing it by the book.
I have been doing the same for many years, put a cup of diesel in a hot engine and run it (without load) for 5 mins before you drain the oil. (diesel is oil you know!)
Originally Posted by DAKA
I also add engine oil to the diesel tank whenever I fill up.
If you are changing your engine oil annually, you are not likely to built up much contamination. Most leisure marine users are doing less than 100 hours between changes.
You are paying top £££ for the correct oil, why waste more money on an additive.
Going in for an oil change or for vehicle servicing can often mean getting upsold on other products. One of these goods, an engine flush, is offered much more frequently than a motor actually needs it. Source for this article: The basics of an engine flush. Engine flush is a useful tool to help prolong the life of your car. You should have knowledge about flushing because if it happens that the technician uses too much pressure or does not use the machine correctly, there is a chance that it could cause damage to the engine which could include blowing out the seals on important engine parts.