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When to Perform an Engine Flush?

Is engine flushing necessary or even desirable and if yes, in which cases - is one of the most common unknowns vehicle owners are faced with. We have put our effort into answering this question, as well as many others regarding this topic, in association with Dr. Stevan Dimitirijevic, a bachelor of chemical technology and Faculty of Technology and Metallurgy’s Innovation Center’s research associate, who also happens to be the author of this text.

The first thing to state is:

Engine flushing is an unnecessary procedure, assuming you perform oil and filter change on a regular basis or if you use types of oil whose quality meets or supersedes the manufacturer’s requirements.

When to Perform an Engine Flush


Have in mind that, in this case, regular oil change also includes shorter change intervals, when a vehicle is used in severe exploitation conditions. Such conditions are defined by the vehicle’s instruction manual and they include: frequent trailer towing, frequent city driving with a lot of coasting, using the vehicle primarily for short distances (especially in wintertime), driving at high altitudes or on dusty roads.



Engine flushing is usually related to occupations which require a vehicle being used professionally, such as: taxi service, delivery service, communal or police service etc. In case you’re not certain, have a look at the vehicle’s construction manual or contact the manufacturer’s representative.

When to Perform an Engine Flush


Engine flushing, in 95% of the cases, is completely unneeded and in 99% (probably 100%) is unnecessary. Therefore, the real need for this procedure falls into (as far as the implementation frequency is concerned) the category of “statistical error”.

Still, a lot of people are indecisive about it due to the fact that not only are there dozens of engine flush products available to us, but there are also some well-known brands among the manufacturers.

When to Perform an Engine Flush


When Do You Really Need to Perform an Engine Flush?

This is difficult to evaluate and it can only be determined by a professional vehicle service. Usually, it applies to the cases of irregular vehicle maintenance, especially irregular oil change. The procedure itself, as well as the products for it, is meant for the purpose of flushing out the engine deposits (mostly coke and organic paints), which come as a consequence of engine oil degrading. This kind of intervention was far more needed several decades ago, whereas now, much more efficient additives are used, thus preventing the aforementioned occurrences from taking place, even when service intervals are exceeded (this particularly applies when it comes to the use of synthetic types of engine oil).

The engine flushing procedure can be performed in more ways than one and the most frequent way is the use of additives, which are added just prior to an oil change, and then, after a few minutes of coasting, the additive-enriched oil is released. Back in the day, special engine flush types of oil used to be implemented, usually ones containing less detergent and dispersant (SAE 10W or SAE 20). They were normally poured into the engine after the oil release and then, after low-resistance engine running (usually in coasting mode) and after some time had gone by, they were released. This was all followed by filter replacement and oil filling, in accordance with the manufacturer’s recommendation. There are also additives which are added into oil and which require that you drive your vehicle a few hundred kilometers before you release and replace the oil.

One of the dominant opinions from back in the day is that, when switching from one type of oil to another (for example, a switch from mineral to synthetic), it is necessary to flush the engine. However, modern types of oil, by eminent world manufacturers, possess such quality that they completely eliminate the need for the aforementioned procedure.

Exceeding a service interval one time is usually no reason to perform an engine flush (unless the interval has been exceeded significantly). It is only if you haven’t changed oil on time several times in a row (which is extremely damaging to you engine), that you can take this procedure into consideration. However, in these kinds of cases (or as a prevention), it is maybe enough (and better) to shorten an oil change interval once and then go on in accordance with the regular schedule.  

This kind of do-it-yourself procedure is more of an extended care and it doesn’t solve what are, in this case, piled up problems. If you’re going to perform an engine flush, make sure you use well-known brands and consult the manufacturer. If, however, the engine is “coked up (if it contains a lot of deposits)”, flushing it won’t solve the problem. In that case, it’s advisable to go to a professional vehicle service, which can handle it with the use of special machines or by cleaning, while only partially disassembling the engine. There are exceptional cases of engine negligence, which result in having to go through an engine repair.

It is usually stated that it is good to perform an engine flush if there is a documented poor-maintenance record or if a vehicle with an unknown maintenance history has been purchased (without a service book). Regardless of that, in such cases, it’s best to consult a professional vehicle service, which will determine the need and the procedure for engine cleaning.



When to Perform an Engine Flush


One of the very few situations, which makes engine flushing a desirable procedure, is when driving a vehicle on a race truck, even if it’s for recreational purposes, when oil is not changed within short intervals, but only within moderately short ones. Professional teams change oil much more frequently, depending on the need and following each race. They usually do NOT perform engine flushing.

Modern engine flush products’ function is based more on detergent and less on dissolving qualities, which makes them safe for use. Normally, they don’t react negatively to sealing gaskets, unless they’re already in bad condition. Still, it remains that the engine flushing procedure is often unnecessary and incomplete, which makes the use of additives questionable at all times.


The reason for potential engine flushing can be found within the fact that irregular oil change has become a frequent occurrence at some professional vehicle services, meaning oil change is performed on a cold engine and quickly (within 15 minutes or less), which leads to the engine being left with the backlog of 20% - 30% of the old oil rather than the desired 10%. This, at least according to the advocators of engine flushing, creates, as time goes by, the need for this kind of intervention at every few oil changes.

Official vehicle services or those which care about their reputation will perform oil change in accordance with the procedure which says that, prior to the change, oil must be heated at a temperature of 60 °C to 80 °C and that the backlog of the old oil must be minimal.



It needs to be emphasized that engine flushing works more in a preventive than in a curative way, as well as that, even in such cases, the procedure is performed based on one’s intuition and without solid indicators of the actual need.

Finally, it’s important to say that no vehicle’s instruction manual state the need for engine flushing, which means that the need for the procedure is to be determined by a professional vehicle service.

We hope that you’ve found this article useful. For any questions, unknowns and suggestions you may have, please, feel free to contact us.


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