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Discussion Starter · #1 · (Edited)
Over the weekend, I have read hundreds of posts regarding fuel octane levels. When I picked up my 2000 B5 V6 variant in May, my local indie VW mechanic told me to fill it with AKI 89 octane. I am now convinced of the benefits of premium fuel and will soon make the switch from 89 to 93--we don't get 91 in Wisconsin. However, I still have some questions.

First off, let me try to summize what I have gathered from various discussions on this forum:
- The owner's manual states that 91 is recommend for optimum performance, but that lower grades of fuel (87-90) will work with reduced effieciency and power
- Upon ignition of the engine, the ECU adjusts the timing of the engine for maximum performance until the knock sensors force spark retardation. Therefore, fuels with lower-than-recommended anti-knock indexes will pre-detonate and the engine will knock momentarily until the timing is changed.

Regarding that second point, I have read a few posts that state that the timing is being continuously adjusted. This boggles me. If the computer realizes that the fuel in use is causing the engine to knock, then why would it repeatedly attempt to correct the timing (and cause more knocking in the process) rather than remain at a retarded ignition setting until the engine is turned off. Then, at the next start-up, with the car not knowing what octane-rated fuel you may have just pumped into it, the engine will again adjust the timing for maximum performance.

Along that line, just how much damage has been done to my Passat's engine? The original owner--I am the second owner--religiously used 87 octane for the six years and 94k miles that she had the car. In my purusing of the forums, I noticed a few posts inquiring what if any long-term damage would result from the use of regular gasoline. Does anyone want to check my pistons, rods, and crankcase?

Lastly, I read a few posts from Passat owners in cold climes who use 89 or 90 octane fuel during the winter months. They note that premium fuel causes sluggish performance when that little snowflake on the dashboard illuminates. I live in central Wisconsin, and the average winter temps are in the 20s during the day and teens or single-digits at night. Unfortunately, I have to park my car outside because my cheap apartment doesn't come with an enclosed garage space.

I think I had one final related question, but it decided to get lost in my mind. I'll post it later if I ever remember it.

Thanks much,
Tim.
 

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If I lived in Steven's Point, I'd fill 'er up with Point Beer. :lol: I drank quite a bit of that stuff in College. As I recall, it was "high-octane".

;)

Kenny
 

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Over the weekend, I have read hundreds of posts regarding fuel octane levels. When I picked up my 2000 B5 V6 variant in May, my local indie VW mechanic told me to fill it with AKI 89 octane. I am now convinced of the benefits of premium fuel and will soon make the switch from 89 to 93--we don't get 91 in Wisconsin. However, I still have some questions.

First off, let me try to summize what I have gathered from various discussions on this forum:
- The owner's manual states that 91

***Leaving this computer, will continue shortly from another terminal***
man he bookmarked a thread:whistle:
 

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Discussion Starter · #4 ·
Kenny, I'm sorry to tell you this, but the Point Brewery has a new brewmaster. Point Beer just isn't the same....

man he bookmarked a thread:whistle:
Haha, not really, Scott. I was kicked off a computer here at work, and saving what I had seemed like the best choice. My other options were to copy/paste what I typed into an email to myself (which I didn't really have time to do), or just retype the whole thing. Laziness prevailed.
 

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Lower octane fuel reduces the car's power and efficiency partly because the engine will retard the ignition timing and partly because the turbocharger will have to limit its boost and reduce the compression ratio inside the cylinders. The engine internals are all iron, though, so a little knocking from time to time won't really hurt anything. If you haven't noticed knocking, it's unlikely that there's been enough of it to damage the engine.
 

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Lower octane fuel reduces the car's power and efficiency partly because the engine will retard the ignition timing and partly because the turbocharger will have to limit its boost and reduce the compression ratio inside the cylinders. The engine internals are all iron, though, so a little knocking from time to time won't really hurt anything. If you haven't noticed knocking, it's unlikely that there's been enough of it to damage the engine.
knocking ---
it is from the gas pre-igniting from a hot spot on the piston from using bad or wrong octaine fuel.
the knock is a result of combustion happening before the piston is tdc, it is still on the upstroke.
here you read about it...
http://www.streetrodstuff.com/Articles/Engine/Detonation/index.php
 

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knocking ---
it is from the gas pre-igniting from a hot spot on the piston from using bad or wrong octaine fuel.
the knock is a result of combustion happening before the piston is tdc, it is still on the upstroke.
here you read about it...
http://www.streetrodstuff.com/Articles/Engine/Detonation/index.php
Maybe you're unaware that higher boost pressure can put the air/fuel mixture over the top and cause it to pre-ignite when it wouldn't have otherwise? Which is why the ECU will limit the boost pressure if it detects knocking?
 

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Maybe you're unaware that higher boost pressure can put the air/fuel mixture over the top and cause it to pre-ignite when it wouldn't have otherwise? Which is why the ECU will limit the boost pressure if it detects knocking?
Last time a checked there werent to many boosted v6 passat.

Try again:poke:
 

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My 2001 owner's manual and gas cap door clearly recommend 91 octane, but the sales person said we could use 89 octane. Of course, this is the same dealership that used bulk 5W-30 Castrol dino for free-and-worth-every-penny 1.8T oil changes. :)

I use 91 octane from a reputable supplier, such as Chevron or Shell, and don't lose sleep over gasoline. (We don't have 93 octane in California, and I am not convinced the Passat is designed to take advantage of it, anyway. My 2003 Dodge Stratus is designed for 87 octane gasoline, and that's what it gets.)
 

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The engine internals are all iron, though, so a little knocking from time to time won't really hurt anything. If you haven't noticed knocking, it's unlikely that there's been enough of it to damage the engine.
Not wanting to doubt anothers intelligence, but I thought that most reciprocating parts (piston, connecting rods) were made from some type of aluminum alloy. I know for sure that the head is made from aluminum, and the block is cast iron on the 1.8t. The only automobile engine I have seen apart recently is an Alfa Romeo 3.0L SOHC v6. This engine definitely had aluminum pistons. Although this could be a rare design as it also has wet liners. Or, am I off base here on the whole aluminum piston/con rod thing?:crazy:
 

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Discussion Starter · #15 ·
My bad. So, if he's got a V6, why is he sweating the difference between 89 and 93? It's 87 stored in rusty Wisconsin gas tanks that he should be worried about.
And that's exactly what I'm concerned about. The original owner filled it with 87 octane for over 93k miles.

Starting today, I'm mixing 89 & 93 at the pump.
 

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And that's exactly what I'm concerned about. The original owner filled it with 87 octane for over 93k miles.

Starting today, I'm mixing 89 & 93 at the pump.
OH. I see. If you're really worried, drain the gas tank and change the gas filter. Given that you live in the rust belt, DEFINITELY change the gas filter.
 

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Not wanting to doubt anothers intelligence, but I thought that most reciprocating parts (piston, connecting rods) were made from some type of aluminum alloy. I know for sure that the head is made from aluminum, and the block is cast iron on the 1.8t. The only automobile engine I have seen apart recently is an Alfa Romeo 3.0L SOHC v6. This engine definitely had aluminum pistons. Although this could be a rare design as it also has wet liners. Or, am I off base here on the whole aluminum piston/con rod thing?:crazy:
I know the crank is made of steel. I very, very seriously doubt that the pistons and the rods are made of anything but steel, because aluminum doesn't have a fatigue threshold -- that is to say, whereas steel has to suffer impact above a certain amount of force before anything bad will happen to it, aluminum will eventually fail regardless of impact force. You can LITERALLY tap a piece of aluminum on a tabletop over and over and it will break eventually. Steel won't. Consider the number of impacts the connecting rods have to endure as part of their job and you'll see why even the best aluminum in the universe would be insufficient.
 

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I know the crank is made of steel. I very, very seriously doubt that the pistons and the rods are made of anything but steel, because aluminum doesn't have a fatigue threshold -- that is to say, whereas steel has to suffer impact above a certain amount of force before anything bad will happen to it, aluminum will eventually fail regardless of impact force. You can LITERALLY tap a piece of aluminum on a tabletop over and over and it will break eventually. Steel won't. Consider the number of impacts the connecting rods have to endure as part of their job and you'll see why even the best aluminum in the universe would be insufficient.
etiher go to automotive school or read about things before you post.
aluminum pistons & connecting rods are very common these days.
nascar uses bolth and so do 2400 hp funny cars.
 

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I know the crank is made of steel. I very, very seriously doubt that the pistons and the rods are made of anything but steel, because aluminum doesn't have a fatigue threshold -- that is to say, whereas steel has to suffer impact above a certain amount of force before anything bad will happen to it, aluminum will eventually fail regardless of impact force. You can LITERALLY tap a piece of aluminum on a tabletop over and over and it will break eventually. Steel won't. Consider the number of impacts the connecting rods have to endure as part of their job and you'll see why even the best aluminum in the universe would be insufficient.
I did some research on this last night. It appears as aluminum is the norm for pistons and con rods in most street applications. The ductility of the aluminum apparently works better because it "gives" alittle when some pre ignition occurs, most steel would just break. Titanium is being used as a con rod material more often now. I think Honda was the first to use it in a massproduced vehicle, the Acura NSX.
This is why preignition is bad. If left unchecked, piston damage could result.

As for the rusty Wisconsin gas, this past summer I had numerous tanks of bad 93 octane in my motorcycles. When gas was $3 a gallon, no one purchased the 93 octane. So it sat under ground for who knows how long, collecting who knows what. The 87 octane stuff is used by the vast majority of the motoring public. so it is more fresh. Lets just say the stations that gave me trouble, I have not visited since. And don't forget in the cooler, denser winter air, detonation is less likely to occur, so a tank of 87 octane every now and then should not do any lasting damage.
 

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My past experiance with the V6 (modified - intake, chip, UDPs: in SW FL) was to run 93.
Time of year didn't matter much, other than occasional "flutter" under heavy acceleration during summer months when the temperature and humidity were in the high 90's.
 
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