jons2art

When I purchased my Q5 a few months ago the dealer suggested I use "top tier" gas retailers (found at toptiergas.com) as these brands had the detergents that were better able to clean Audi fuel injectors. The octane level was not as important (even though inside the gas tank cover it says 95 octane). Is there much difference in performance, engine wear, or gas milage if you compare high octane "top tier" with low octane non-detergent gas? I've been using 89 top-tier and getting 24-25 mpg.

Heresy64

I'm neither a scientist nor a mechanic, but I want to explain in simple terms (because that's how I understand it) a little about the fuel you put in your car.

First, I'm not sure where you're from, but in the US, there is no 95 octane fuel. In fact, if you check the sticker inside your fuel filler door, you'll see a couple of different numbers specifying the octane. 95 refers to the European method of determining the octane and is roughly equivalent to 91 octane in the states. Ignore the octane numbers and just use "super" or "premium" gasoline. If you want to compare numbers, the yellow sticker on the gas pump will tell you the octane and the method used to calculate it. You can match that with the octane recommendation on your car.

Second, don't confuse fuel quality with octane. Top-tier gas has nothing to do with octane, but with the detergents in the fuel. Detergents have nothing to do with how the fuel burns in your engine, they merely keep the fuel system cleaner.

Octane determines how fuel burns in your engine. High-compression engines (especially turbocharged engines) require high-octane,or premium, gasoline. Lower octane fuels will not burn as well in the engine and cause what is known as detonation (not good). The computers in the engine recognize the detonation and will adjust the compression to eliminate the problem, reducing both power and efficiency. While you're not likely to damage the engine running lower octane fuels (due to the computer's compensation) you will not be getting the most out of your engine and your power and fuel economy will likely suffer.

I may get flamed for this, but my rule is octane first, top-tier second. IMO, premium gas from a non-top-tier vendor is better than mid-grade or regular gas from a top-tier vendor. If you can get both, great.

My advice would be to not try to save a couple of bucks by using lower octane fuel. Use premium and your engine will love you. Use premium top-tier and your engine will love you more. Use lower octane gas of any kind and your engine will hate you. I mean, really, you're driving a $45k car. I think you can spring for the extra three bucks a tank that premium gas costs.

serranot

Detergent is just a cleaner for the injectors; it won't affect the mileage (at least in the short-term) and has nothing to do with octane.

Octane is a numerical representation of the fuel's ability to resist detonation. My guess is that the inside of your filler cover also has the US requirements (91 I think). The engine management system has the ability to detect detonation and retard the timing accordingly to prevent the detonation. But you will get reduced performance from the engine, and mileage can suffer.

Of the two things, I would first worry about octane and then detergent. A lower octane can theoretically cause engine-damaging detonation; lack of detergent in a particular tank of gas is really going to have no meaningful effect. One tank of lower octane gas probably won't do bad or lasting things, but I don't recommend using lower octane on a consistent basis and neither does Audi.

Huey52

Good info; would just add that it indicates 91 Premium octane(with a 95 RON) on the placard inside the fuel filler door for the 2.0T.

The ECU will auto retard the timing (and thereby performance) for lower octane fuel, which may be why your salesman indicated the Top Tier detergent (for injector, etc. cleaning) is more important than octane if you have to make a choice.

js from nc

At my last service (50k) my rep recommended a fuel injectors clean out ($180). I had that done at 25k and I did notice a difference. Since then I have made it my business to use top tier premium and do not believe I have a performance or mileage issue. So my question is: should we get the service only when performance appears down, or no matter what based on mileage?

The G Man

In my opinion, its pretty important to use recommanded octane grade in an Audi since most direct injection engine have carbon build up problems. The recommanded grade will help the combusion proccess burn more completly, therefore creating less carbon up. With that said, I only use Shell V-Power in my Audi.

Reggie

I have always used top tier manufactures in my car - for several reasons:
1. They control all of the supply chain and hence have a vested interest in not letting dirt, water, oil into the supply.
2. They invest in the additives to keep the injectors clean.
3. Many of the smaller chains buy gas from the cheapest suppliers with little quality control.

That said there have been cases (including shell and texaco I believe) in the south where they had bad gas that ruined injectors in many cars.

JFA in L.A.

Buy premium gas at a high-volume gasoline retailer. Period.
Additives in gasoline are in such minute quantities, they are much better for marketing, than they might be for your engine.
Gas outlets like Costco are getting no-label truck deliveries of Shell gasoline one day, and maybe Chevron the next. In L.A., all gas comes from two refineries. ALL gas.
Costco sells so much gas, so fast, you'll never get a bad batch (condensation, debris, sludge), which is the biggest threat to your car from filling up.
If you've just got to pay more for Techron, or whatever, Big Oil loves you.

HaveBullDogWillTravel

Completely disagree. I'm not one to believe everything I read on the internet(like what's written above) but I do believe in Top Tier Fuel.
http://www.toptiergas.com/deposit_control.html

JohnBoyToo

HBWT - love that you are using an internet link to support that you don't believe everything you read on the internet, love your tongue-in-cheek ref !

Just like global warming, er, ah, climate change.... there are experts on both sides of the argument, some theorist and some realist.... your car, you get to do what you want with it (so far !)

Carbon typically doesn't have a chance to form in any car my wife drives !!!
Hard acceleration and high heat usually will 'clean' that out...

just like the breads a company I did some 4gl work for - the same loaf of bread had upwards of 50 wrappers and 50 prices - MANY fuel stations have the same fuel...

as stated, the key is turn over - always best to go to a high volume station.

stated that the excellent designers put together an engine that requires premium fuel, but yet didn't those same excellent designers do the anti-knock sensors ?

The main reason for prem requirements is that to get the MPG and HP advertised by the mfg's you must use prem fuel... use regular and get 1 hp less and maybe a mpg less.... just one side of the coin...