Engine flush and fuel additives: Are they worth the money or not?

Engine flush

Regular oil and filter changes should be a routine part of car ownership

When it comes to finding out whether drivers should use engine flush products or fuel additives, the internet will send you round in circles. Some say the products, added to a car’s oil or fuel to clean the engine’s internal moving parts and boost performance, are worth their weight in motor-protecting gold. Others claim they’re not worth the time or the effort.

The basic theory behind both these kinds of products is that by running them through the engine, you’ll clean out any deposits left by the engine’s combustion process. Proving whether they work is easier said than done. Here’s what the experts say.

Engine flush: Why having a cleaner engine is beneficial

Nick Reid, Green Flag technical expert and the company’s head of transformation, explains why someone might want to clean their car’s engine: “The dirtier an engine is, the less thermally efficient it will be. Deposits on the pistons and in the combustion chambers will drive up hydro carbon emissions. In a petrol engine this will mean the catalytic converter will have to work harder and so will have to be replaced sooner.”

Engine flush: What an engine flush maker says:

“STP Engine Flush is specially formulated to rapidly dissolve harmful engine deposits and maintain efficient oil circulation throughout the entire engine, helping to protect vital engine wear surfaces throughout the flush.”

Engine flush: The retailer’s point

Dave Swaysland, fuel additives expert at Halfords, said: “We’d advocate using engine flush prior to an oil change to remove sludge and other contaminants from key parts of the engine. Using engine flush prior to changing oil means that you’re cleaning the entire system and not contaminating the new oil that you’re about to put in, keeping your car running smoothly. Clearly the longer you leave it between oil changes the more important using an engine flush is. Also the older the car, the more chance of sludge build up.”

Engine flush

Adding an engine flush to your car could invalidate its warranty, says Ford

Engine flush: Could lead to warranty woe, says Ford

We asked Ford for its view of after-market engine flush products. It said: “Do not use oil additives or other engine treatments. Under certain conditions, they could damage the engine. If you do use one and there is a subsequent engine problem, your warranty will no longer be valid.”

Engine flush: Why car makers do not recommend them

Engine flush and additive products are essentially chemicals. These then react with any leftovers in the engine to strip them out. In the case of a flush, you empty them out; for additives, any waste is burnt off. The reason car makers don’t approve is that they’re concerned some of these chemicals may react with rubber or plastic components in the engine and cause premature ageing and failures.

Engine flush: Verdict

Green Flag technical expert Nick Reid said: “These products really are a case of ‘you pays your money, you takes your choice’. I believe some have a pure placebo effect on drivers: they see a positive result because they want to justify the lengths they’ve gone to. Some products may offer some marginal gains in performance. But I don’t think a regular, everyday driver will see a huge difference.

“If you really want to keep your car working as efficiently as possible, I would suggest you’ll be just as well keeping on top of your oil and filter changes. The cleaner your filters are, the cleaner the inside of the engine will be. It’s simple: the more dirt you let in, the more dirt you’ll have to clean out. If you look after your engine with regular servicing, you really shouldn’t need to do any remedial work.”


5 comments on “Engine flush and fuel additives: Are they worth the money or not?

  1. gray 27/06/2016 10:31 PM

    After BMW ccv valve failed and oil gone though the engine you can buy engine fluse for piston rings etc is this worth doing then

  2. David Rowarth 21/10/2016 11:34 AM

    What products are available to add to fuel remaining in a tank if a vehicle is to be laid up for a period of time. I am about to sorn my motorbike for the winter & last winter I suffered expensive damage to the carbs, o-rings, washes, gaskets etc through the corrosive effect of the remaining petrol in the system. I believe there is a product, American I think,,which protects against the caustic effect of ‘modern’ petrol.

    • jamie simpson 11/11/2016 7:06 AM

      the best thing you can do is to drain your tank completely and drain the float bowls on the carb’s. that way there is no liquid inside that can expand during below 0 temperatures. have seen alot of acrb related problems over the years with customers bikes, but if your bike has a coolant line running into the carb to prevent icing it is also a good idea to make sure your coolant/antifreeze mixture is correct for the weather conditions you are having. for winter storage i personally have a mixture of 50/50 for storing my bikes over winter. another thing, is if it is kept in a garage, do not put a waterproof cover over it as this will trap condensation and attract even more ice to the bike, also if you try to remove it when frozen it could possible damage your paint.

  3. Keith Brown 08/03/2018 11:05 PM

    Good quality oil manufacturers spend a lot of time and money on research to give the best lubricating and cleaning properties to their products. The same goes for the fuel manufacturers. Buying a fuel additive is just a waste of money. As to flushing an engine out prior to an oil change, I think the man from Ford is absolutely spot on. A better thing to do to extend engine life, in my humble opinion, is to halve the oil and filter change intervals. Service intervals of 20,000 miles are really at the limits of any oils usefulness and it is pretty degraded and out of viscosity tolerance by this time, as well as being pretty filthy and acidic. By changing the oil and filter more often to say 10,000 miles the oil is less degraded and more effective and cleaner, which should lead to better engine protection so less wear and longer engine life.

  4. Michael Smith 29/06/2020 10:59 PM

    I note this article is a few years old now, but I have just had my Ford Fiesta (18 reg) serviced at a Ford dealer and would be interested on your view on this. They told me Ford recommend an injection cleaner and oil conditioner as part of the service. Part of their reasoning was that most people buy their petrol at supermarkets and that supermarket petrol does not contain the additives you get at branded petrol stations.

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