"A motor oil can only clean the first layer of contamination" - Terry Dyson, Dyson Analysis
"Flush" is perhaps an overused and misunderstood term. I prefer the term: "cleaning", or more precisely "internal engine oil system cleaning". A clean engine allows the oil to do the intended job.
Solvent Flushes - Some engine flush products and systems can be harmful to your engine and really don't clean as well as advertised. I will not comment on the various machines and proprietary solvents used at lube centers and some auto repair shops other than the idea of aromatic solvent under pressure flowing through an engine does not appeal to me. Solvent under pressure could potentially dislodge large chunks of deposits, clogging passages with little chance of further dissolving. There is also concern with this pressure on seals. The solvent products used only under idle conditions are generally safer than the pressure flushes, but under NO circumstances would I recommend driving with these solvent products or diesel fuel, ATF, or other "cleaning product" in the crankcase that severely dilutes, thins and shears motor oil. Lastly there is always the question of how much solvent remains. This is certainly a concern. Always allow a long drain period to allow the diluted oil to run out (which it should readily do) but also allow the aromatics to evaporate from the warm opened engine. Following a treatment with a good solvent cleaning, I recommend a short oil change interval. AMSOIL engine flush is an idle only product that is not harmful but does fall short in the actual cleaning performance. AMSOIL engine flush is simply poured into the crankcase (after installing a NEW oil filter), the engine is idled 15 minutes, shut down, then drained for as long as possible with filter removed.
Tear down and clean - This would be good if you could, but it usually requires a few weekends, some big cash, some thick books, many years of knowledge and maybe a little intestinal fortitude. Usually advised only if you have a mechanical problem, a problem that requires tear down anyway. Not practical for your otherwise fine running Volvo turbo, Lexus or Suburban.
Synthetic oil cleaning- Synthetic oil alone will clean some areas of your engine, some areas where oil pools and even some oil galleys will be cleaned a bit with synthetic oil alone. Some issues with this, the cleaning will be slow at best, and even though it may not sound logical - this cleaned contamination will be put into suspension in your oil and reduce the time you can use the oil via contamination. Another issue, is that some areas just will not be cleaned with the oil alone. A good example are the ring grooves and the surfaces of the rings.
Additive cleaning- This is a new area of engine cleaning. Most of the chemistry is relatively new, but don't let that scare you, because A) it is very safe B) the ester based compounds are natural. I highly recommend a product called Auto-Rx® . The usage instructions, which are updated periodically on the Auto-Rx® web page, are subdivided somewhat logically into low/high mileage treatment categories. This makes sense because cars with more miles will have a tendency to have dirtier engines, but car and engine type, driving style, maintenance routines, oil variety also play large roles in how much dirt and sludge will be built up. A car with under 50,000 miles of stop and go driving with petroleum oil changed at 8,000 mile intervals (if the owner remembers) could have a sludge problem that needs cleaning.
So why clean your engine?
If you are switching over to synthetic oil, some of the benefits will become much more apparent if you start with a clean engine. Longer oil change intervals, better cooling, more power are just a couple key characteristics that are enhanced if old petroleum oil residues are removed. Just changing to any synthetic oil will not completely clean your engine - honestly I used to think this - but there are just some locations in the engine that oil won't clean. Auto-Rx® will clean these areas and allow the synthetic oil to keep the rings free floating, thus allowing a better compression seal and result in more power and less emissions, for example.
If you start with a seriously clean engine your oil will last longer and frankly will protect the engine better. Many of the deposits and crud, and especially the more harmful by-products of petroleum oil oxidation tend to have an acidic reaction. This will deplete the additives in any motor oil.
OUTLINE OF MY BASIC THOROUGH HIGH MILEAGE INTERNAL ENGINE CLEANING PROCESS
This process applies to the worst case scenario car. The project car. It's not necessarily risky but only the first portions apply to a well maintained vehicle simply changing over to synthetic oil. If you are simply changing over a relatively well maintained car to Amsoil the regular or high mileage Auto-Rx® treatment will be great.
Those of you familiar with my earlier 2000-2002 version that covered fuel injector cleaning during the engine cleaning process, I have left this out for sake of clarity. Again this process takes a bit of patience, attention to detail and some driving miles. If you have any questions don't hesitate to ask.
1) Acquire 3 bottles of Auto-Rx® (ideally do the 3 for the price of 2 deal), 1 can of Amsoil engine flush, enough good quality inexpensive petroleum motor oil (Chevron products seem to work well for this) for 4 changes, 5 filters and your Amsoil motor oil.
2) Run the high mileage application instructions per the Auto-Rx® instructions. (7/20/03 sample instructions below) This will use two of the bottles of the Auto-Rx® and in most circumstances will be all you need to the clean engine very well. If you know the engine to be very dirty or the engine did not have good oil/oil service history do not change to synthetic yet, just fill with the dino oil at the end of the second Auto-Rx® application.
FIRST APPLICATION
STEP
1
Install new oil filter (DO NOT BYPASS THIS STEP. You will need
a clean
oil filter to catch and store liquefied contaminants coming out of your engine).
STEP 2
Pour full 12 ounces of Auto-Rx® ® into your
existing oil.
STEP 3
Drive 750 miles
Drive 1000 miles if your vehicle has a diesel engine
STEP 4
Change the oil and oil filter.
STEP 5
Drive your car an additional 1500 miles with just the new oil and
filter.
SECOND APPLICATION
STEP
1
Add the second bottle of Auto-Rx® ® (do
not change oil filter yet)
STEP 2
Drive 750 miles
Drive 1000 miles if your vehicle has a diesel engine
STEP 3
Change the oil (dino) and oil filter.
3) Drive 500 -1000 miles.
4) Do the Amsoil oil flush treatment (no need to use a new filter) allow to idle for 15 minutes.
5) Shut engine down, carefully drain hot solvent diluted oil. Remove filter. Remove oil fill cap (loosely cover hole to allow venting without introducing contamination). Allow to drain as long as possible, overnight would be OK.
6) Install new filter, drain plug, dino oil and last (3rd) bottle of Auto-Rx®.
7) Drive 1000 miles.
8) Change oil to Amsoil synthetic oil, new filter and drive 5000 miles or longer WITH an oil analysis at 5000 miles maximum - and a filter change - after sampling the oil (if the oil isn't drained, sample obtained and filter changed.)