hoeser

The forced induction engines (2.0T) are less prone to buildup because they are forced induction, which makes sense. More pressure in the manifold, less exhaust gas recirc... etc. I have read the 3.2 is just as bad as the 4.2. Wish I knew that before I bought the 3.2... but I fell in love with the sound and I absolutely love the torque curve.

adamstasiak

Ok I hear you.
Stop going to Shell for gas unless you have emergency. Use Castrol non synthetic oil. This will make you smile again.

Stevelev

Yup, that's the perfect solution for a B5 A4

hoeser

Yep... and not very good advice for a B7 FSI A4 unfortunately. I would never put non synthetic oil in this car.

On an aside, I generally only put Ultra 94 in my car anyway. I still add seafoam just cause'... love that stuff, it will at least keep the cylinder heads and top of the pistons clean...

Stevelev

I was being sarcastic and pretty sure adamstasiak was too

adamstasiak

Sorry guys I am not sarcastic at all. I just told you what worked for me over 25 years dealing with VW and AUDIS.
When it comes to gasoline there is Octane# and Cetane#. I find 94 Octane too high. The cetane# is too low. The car does not accelerate right away as this gas burns too slow. As far as I am concerned 92 is just right.

plg_cp

But Shell is the one without Ethanol...

adamstasiak

I do no know what is wrong with Shell.
They make good gasoline in Europe.

mikeh

I have done some research into different fuels and the ethanol question. Since doing the research I only use Shell 91 because of the no ethanol content. Here is a synopsis of some of the research.

Ethanol-based engines
Ethanol is most commonly used to power automobiles, though it may be used to power other vehicles, such as farm tractors, boats and airplanes. Ethanol (E100) consumption in an engine is approximately 51% higher than for gasoline since the energy per unit volume of ethanol is 34% lower than for gasoline.[20][21] However, the higher compression ratios in an ethanol-only engine allow for increased power output and better fuel economy than could be obtained with lower compression ratios.[22][23] In general, ethanol-only engines are tuned to give slightly better power and torque output than gasoline-powered engines. In flexible fuel vehicles, the lower compression ratio requires tunings that give the same output when using either gasoline or hydrated ethanol. For maximum use of ethanol's benefits, a much higher compression ratio should be used,[24] Current high compression neat ethanol engine designs are approximately 20-30% less fuel efficient than their gasoline-only counterparts.[25]

A 2004 MIT study[26] and an earlier paper published by the Society of Automotive Engineers[27] identify a method to exploit the characteristics of fuel ethanol substantially better than mixing it with gasoline. The method presents the possibility of leveraging the use of alcohol to achieve definite improvement over the cost-effectiveness of hybrid electric. The improvement consists of using dual-fuel direct-injection of pure alcohol (or the azeotrope or E85) and gasoline, in any ratio up to 100% of either, in a turbocharged, high compression-ratio, small-displacement engine having performance similar to an engine having twice the displacement. Each fuel is carried separately, with a much smaller tank for alcohol. The high-compression (which increases efficiency) engine will run on ordinary gasoline under low-power cruise conditions. Alcohol is directly injected into the cylinders (and the gasoline injection simultaneously reduced) only when necessary to suppress ‘knock’ such as when significantly accelerating. Direct cylinder injection raises the already high octane rating of ethanol up to an effective 130. The calculated over-all reduction of gasoline use and CO2 emission is 30%. The consumer cost payback time shows a 4:1 improvement over turbo-diesel and a 5:1 improvement over hybrid. In addition, the problems of water absorption into pre-mixed gasoline (causing phase separation), supply issues of multiple mix ratios and cold-weather starting are avoided.

Ethanol's higher octane rating allows an increase of an engine's compression ratio for increased thermal efficiency.[22] In one study, complex engine controls and increased exhaust gas recirculation allowed a compression ratio of 19.5 with fuels ranging from neat ethanol to E50. Thermal efficiency up to approximately that for a diesel was achieved.[28] This would result in the fuel economy of a neat ethanol vehicle to be about the same as one burning gasoline.

Since 1989 there have also been ethanol engines based on the diesel principle operating in Sweden.[29] They are used primarily in city buses, but also in distribution trucks and waste collectors. The engines, made by Scania, have a modified compression ratio, and the fuel (known as ED95) used is a mix of 93.6 % ethanol and 3.6 % ignition improver, and 2.8% denaturants.[30] The ignition improver makes it possible for the fuel to ignite in the diesel combustion cycle. It is then also possible to use the energy efficiency of the diesel principle with ethanol. These engines have been used in the United Kingdom by Reading Transport but the use of bioethanol fuel is now being phased out.

[edit] Engine cold start during the winter

The Brazilian 2008 Honda Civic flex-fuel has outside direct access to the secondary reservoir gasoline tank in the front right side, the corresponding fuel filler door is shown by the arrow.High ethanol blends present a problem to achieve enough vapor pressure for the fuel to evaporate and spark the ignition during cold weather (since ethanol tends to increase fuel enthalpy of vaporization[31]). When vapor pressure is below 45 kPa starting a cold engine becomes difficult.[32] In order to avoid this problem at temperatures below 11 ° Celsius (59 °F), and to reduce ethanol higher emissions during cold weather, both the US and the European markets adopted E85 as the maximum blend to be used in their flexible fuel vehicles, and they are optimized to run at such a blend. At places with harsh cold weather, the ethanol blend in the US has a seasonal reduction to E70 for these very cold regions, though it is still sold as E85.[33][34] At places where temperatures fall below -12 °C (10 °F) during the winter, it is recommended to install an engine heater system, both for gasoline and E85 vehicles. Sweden has a similar seasonal reduction, but the ethanol content in the blend is reduced to E75 during the winter months.[34][35]

Brazilian flex fuel vehicles can operate with ethanol mixtures up to E100, which is hydrous ethanol (with up to 4% water), which causes vapor pressure to drop faster as compared to E85 vehicles. As a result, Brazilian flex vehicles are built with a small secondary gasoline reservoir located near the engine. During a cold start pure gasoline is injected to avoid starting problems at low temperatures. This provision is particularly necessary for users of Brazil's southern and central regions, where temperatures normally drop below 15 ° Celsius (59 °F) during the winter. An improved flex engine generation was launched in 2009 that eliminates the need for the secondary gas storage tank.[36][37] In March 2009 Volkswagen do Brasil launched the Polo E-Flex, the first Brazilian flex fuel model without an auxiliary tank for cold start.[38][39]

[edit] Ethanol fuel mixtures
For more details on this topic, see Common ethanol fuel mixtures.

Hydrated ethanol × gasoline type C price table for use in BrazilTo avoid engine stall due to "slugs" of water in the fuel lines interrupting fuel flow, the fuel must exist as a single phase. The fraction of water that an ethanol-gasoline fuel can contain without phase separation increases with the percentage of ethanol.[40]. This shows, for example, that E30 can have up to about 2% water. If there is more than about 71% ethanol, the remainder can be any proportion of water or gasoline and phase separation will not occur. However, the fuel mileage declines with increased water content. The increased solubility of water with higher ethanol content permits E30 and hydrated ethanol to be put in the same tank since any combination of them always results in a single phase. Somewhat less water is tolerated at lower temperatures. For E10 it is about 0.5% v/v at 70 F and decreases to about 0.23% v/v at -30 F.[41]

In many countries cars are mandated to run on mixtures of ethanol. Brazil requires cars be suitable for a 25% ethanol blend, and has required various mixtures between 22% and 25% ethanol, since of July 2007 25% is required. The United States allows up to 10% blends, and some states require this (or a smaller amount) in all gasoline sold. Other countries have adopted their own requirements. Beginning with the model year 1999, an increasing number of vehicles in the world are manufactured with engines which can run on any fuel from 0% ethanol up to 100% ethanol without modification. Many cars and light trucks (a class containing minivans, SUVs and pickup trucks) are designed to be flexible-fuel vehicles (also called dual-fuel vehicles). In older model years, their engine systems contained alcohol sensors in the fuel and/or oxygen sensors in the exhaust that provide input to the engine control computer to adjust the fuel injection to achieve stochiometric (no residual fuel or free oxygen in the exhaust) air-to-fuel ratio for any fuel mix. In newer models, the alcohol sensors have been removed, with the computer using only oxygen and airflow sensor feedback to estimate alcohol content. The engine control computer can also adjust (advance) the ignition timing to achieve a higher output without pre-ignition when it predicts that higher alcohol percentages are present in the fuel being burned. This method is backed up by advanced knock sensors - used in most high performance gasoline engines regardless of whether they're designed to use ethanol or not - that detect pre-ignition and detonation.

[edit] Fuel economy
In theory, all fuel-driven vehicles have a fuel economy (measured as miles per US gallon, or liters per 100 km) that is directly proportional to the fuel's energy content.[42] In reality, there are many other variables that come in to play that affect the performance of a particular fuel in a particular engine. Ethanol contains approx. 34% less energy per unit volume than gasoline, and therefore in theory, burning pure ethanol in a vehicle will result in a 34% reduction in miles per US gallon , given the same fuel economy, compared to burning pure gasoline. Since ethanol has a higher octane rating, the engine can be made more efficient by raising its compression ratio. In fact using a variable turbocharger, the compression ratio can be optimized for the fuel being used, making fuel economy almost constant for any blend. .[20][21] For E10 (10% ethanol and 90% gasoline), the effect is small (~3%) when compared to conventional gasoline,[43] and even smaller (1-2%) when compared to oxygenated and reformulated blends.[44] However, for E85 (85% ethanol), the effect becomes significant. E85 will produce lower mileage than gasoline, and will require more frequent refueling. Actual performance may vary depending on the vehicle. Based on EPA tests for all 2006 E85 models, the average fuel economy for E85 vehicles resulted 25.56% lower than unleaded gasoline.[45] The EPA-rated mileage of current USA flex-fuel vehicles[46] should be considered when making price comparisons, but it must be noted that E85 is a high performance fuel, with an octane rating of about 104, and should be compared to premium. In one estimate[47] the US retail price for E85 ethanol is 2.62 US dollar per gallon or 3.71 dollar corrected for energy equivalency compared to a gallon of gasoline priced at 3.03 dollar. Brazilian cane ethanol (100%) is priced at 3.88 dollar against 4.91 dollar for E25 (as July 2007).

audishiva

I just did a 3000 + KM trip around the North shore of Quebec and Gaspe and used fuel from Petrocan, Ultramar, Esso and others. Most times there wasn't any choice as there was only one gas station in the town. The car is a 2007 A4, 3.2 MT and the trip allowed me to really see what the car could do since there is a lot of hill and curve driving. Nothing quite like passing cars on a 10% grade 3Km long hill while in 6th gear.......

Typically I use the ethanol blend fuel, which I think is E10, 91 octane, from MacEwan's and the car runs like a champ. On this trip, after fueling up with 87 grade, I went into CTC and bought an octane booster because the knocking was so bad. Then I remembered the issues with MMT and fueled up with 93 octane from an Ultramar instead. Most of the time, fuel was $1.03 to $1.06 /liter for 87 octane.

Frankly, after doing about 400 KM on that tank and re fueling with 87 Octane, it still ran fine for the rest of the 1200 KM home, so I think the engine computer can adapt reasonably well to whatever you choose to put in it.......depending upon how you drive, of course.

For an opinion on MMT go here:

CanadianDriver Green Scene Feature: MMT gasoline additive