I have heard really mixed opinions about the necessity of engine flushes. My quick research suggested that manufactures do not recommend doing them. In addition, I have heard of extreme cases of blown engines after engine flushes.
My mechanic performed an engine flush on my old car and so far, it seems to be ok.
An engine flush is basically the process in which a mechanic puts chemicals in the engine oil to break down sludge or carbon deposits from old oil. The difficulty with it is that it can break down sludge that had formed over rubber seals and is actually serving as a secondary engine seal.
Furthermore, if your engine has had regular engine oil changes at the specified times, a flush should be totally unnecessary.
If you do have serious sludge build-ups, it could be the best route to take; but you're taking it at a risk. If the sludge is actually protecting the rubber gaskets, you may have a bigger job on your hands replacing them.
I'll do an engine flush as soon as I see it recommended in the factory service manual. My opinion is to let sleeping dogs (and oil particulates) lie.
It sounds like a good idea on the surface, but as explained in the other answer; once an engine is old enough that a mechanic thinks an engine flush would be a good idea, then it's too late. And if the engine flush is not thought of as a good idea.. it's too early.
The exact timing of when to do an engine flush depends on when the mechanics next Boat Payment is due.
I believe a flush is a good thing, just not with chemicals.
I'm disabled so cannot afford a garage to do the easy stuff, but I also get satisfaction from doing things myself. I always do a flush (not with any chemicals or additives) I simply perform a double oil/filter change, I make sure I do it after a run so that the oil is hot, just drain it via the sump and take off the oil filter, when it has all drained out put on a new filter and fill with new oil, a week later I do it all again.
Is it necessary, NO, but I like the fact that my oil never goes black from soot from the EGR system and the cost of doing it twice myself (even with fully synthetic oil) is still less than a quarter a garage would charge me to do it just the once (at least here in the UK) and I know it has been done, unlike some of the horror stories you hear about from the 'specialist' garages.
If I drove a petrol car rather than a diesel van I probably wouldn't.
My understanding of the engine flush process appears to differ from everyone else that has commented or answered so below is my take on it.
An engine flush (engine oil or transmission oil) is the process in which ALL of the oil is drained from the system and re-filled; this does not necessarily mean that additives are added to break down sludge and inadvertently cause issues with seal.
For instance my car has 12 quarts of transmission fluid. If I simply drain it from the bottom I only get 3 quarts so I only have to fill 3 quarts.
If an engine flush is performed then they need to put back in the exact same amount of oil which they took out. So if they truly flushed 12 quarts via an oil vacuum then they need to put back 12 as well. In this lies the problem.
When filling the transmission with oil they might not reach all of the places where they took it from. There are a LOT of nooks and crannies which might not get lubricated unless you knew to specifically target those areas.
If a nook or cranny is left unfilled then YES, you can absolutely experience a blown transmission.
This same principle applies to engines, brake lines, and cooling systems.
Do NOT ever let them talk you into doing an engine flush. At one of my top offs I was told I would need to get my system flushed cause there was a lot of sludge and such. Well I had them do it at my next oil change. 1 week and a day later I'm driving down highway and my vehicle starts to shake, get to gas station. My engine was knocking something bad. Had to end up getting picked up and my vehicle towed back. Which my dad (vehicle guru) and guy who towed it (my good friends friend) have both confirmed that it my engine is shot. Had I not gotten the flush done, I would still have my vehicle
I just did an engine flush with 20 percent Marvel Mystery Oil in my crankcase with fresh Mobil 1. Sure, the low pressure oil light began to flicker after 200 miles, but it disappeared after I changed the oil again. The car is is 23 years old and has 60k miles, all stop-n-go, and the oil was changed on time (so there was no excessive sludge visible on the oil filler neck).
Now, the tachometer no longer fluctuates at idle. I have seen MMO flush correct fluctuating tach on several cars over 30 years. It is most likely because lower piston rings tend to stick on old cars, even if the crankcase oil is changed regularly.
The main risk with a flush is particles dislodge and clog oil passages, especial the oil pump pick-up screen. The best way to prevent any such problems is to change the oil in intervals of 200, 500, 1000 miles when 20% Marvel Mystery Oil is added. It is not necessary to change it so frequently if used before the car reaches 50k miles.
