Gas Treatment vs. Fuel Injection Cleaner

My wife’s 2002 Mazda has 119,000 miles. The engine recently had a tune-up; yet, the engine developed a knock. Before we got to a higher octane fuel, would a gas treatment or fuel injection cleaner additive help? Which should we try, and what’s the difference between a gas treatment and fuel injection cleaner?

there’s no difference, they’re both nonsense. modern gasoline has more than enough detergents to keep the fuel system and intake ports/valves clean. If her car is suddenly starting to knock, then look at where you/she are getting fuel from.

Is this actually related to a column? I can’t find it, tho I admit I didn’t bust my butt trying to.

As someone who worked for STP, I can tell you that the products absolutely do exactly what they claim on the label. (I can’t speak for other companies, only STP) However as JZ notes, the question today is do you need them? The products were developed in an age when fuel refining was not as consistently high quality and fuels didn’t contain detergents and additives. The question is less “Do they deliver the benefits they claim?” but more “Do I really need those benefits in 2016?”

I don’t know if your knocking is due to a dirty fuel injectors, probably not, but it seems like a pretty low cost option to try. Fuel injector cleaner is a single use product (every few months, not every tank). Try and if it helps, great, if not, you’re only out a few bucks.

If that doesn’t work, there are octane boosting products that you should consider (STP makes one). They’re used every tank and use versus buying premium gas comes down to cost per tank. Also, check the gallons a bottle treats: it may treat 40 gallons, but if your tank is 20, it doesn’t work twice as well and you’ve wasted 1/2 your money. Use 1/2 the bottle.

Lastly, when I worked there, STP made a lead-free “lead replacement fuel additive” designed to stop knocking in older cars that required leaded fuel. I checked their website and they no longer offer it. Another company might sell something like it.

BTW- for JZ - I think the products still have a use nowadays. I still use them, but mostly in my boat and small engine motors that don’t run frequently. They help reduce water build up in the fuel and make the motors runs smoother, especially in spring and fall. The fluctuation in temps (warm days, cool nights) often leads to condensation in the gas tank. My car engine isn’t affected, but my lawn mower definitely becomes tough to start.

When I was driving a truck, I always kept a quart of fuel additive in the side box. Whenever the air temperature got to 20°f or below, I’d pour half of it in each fuel tank when I fueled up. Diesel gels when it gets cold and the additive prevents that.

I think an expert needs to address the first couple of sentences. A 2002 car doesn’t really get a “tune-up”. You probably had the plugs and filters replaced, etc. But the “tuning” part doesn’t happen anymore.

I’m hardly an expert, but I’d wonder what went wrong? Are the plug gaps set wrong? Stuff like that.

In addition, modern car computers generally avoid knock. So, something is really off.

Again, not an expert but maybe someone else can opine about this.

Note that there are different gas treatments for different purposes. One of the most common gas contaminants is good old water. From humidity, poor station storage tanks, etc. Symptoms include bouts of hesitation when accelerating. Doesn’t sound like your problem. Note that this is a completely different product from an injection cleaner or octane booster. What you need is based on the cause. That’s the first issue.

Possible spark plugs with the wrong heat range were installed. If the plugs are running hot, they may be causing the knock.

I concur. I have issues when you get the car back from a garage and an issue appears that was not there before. ALL my vehicles have more than 150k miles on them and none knock. Good mechanics over the years. I’ve not used additives in my fuel in a few decades. Not even gasoline de-icer. What is the 10% ethanol in the gas for? Would the 1% methanol added make much of an improvement? Different fuel vendors have additives that may influence your engines. I flat out refuse to use Cenex gasoline and am not to happy with BPs product, not even for small engines. I also had a truck that would lose 10-15% mileage on the changeover from summer blend to winter blend.
Something was not done properly at the garage. Wrong setting, inferior replacement parts, something not tightened to proper torque settings.