Annoying VW Diesel...

Because in Colorado at elevation, things change again. We have 81, 83, and 85 scattered around the state as the lowest octane rating. All are still standard E10-E15. My "regular" is 83 and that's what I run the Prius on. You have to be careful on far trips if you know you're going to the flat landers, you fill up higher than usual and drive down. Even my house is at 8000ft above sea level. Our Prius spends most of its time between 8000ft and 12000ft up.

 

In that case, the danger of knocking from using lower octane is gone because the thinner air means the pressures in the cylinders are lower.
With the turbo, the manual for the Sonic stressed to keep using 87 at those elevations, since the compressor pressurized the cylinders.

 

It's 87 R+M/2 (91 RON). I don't know what they sell in other states, but here most (if not all) gasoline stations sell regular as 85, midgrade as 87 and premium as 91 R+M/2. Strangely there's only a 2 grade difference between regular and midgrade and a 4 grade difference between midgrade and premium, yet pricewise the difference between regular and midgrade is the same or at times greater than the price difference between midgrade and premium.

Anyhow, here's what the manual says:

So yes. I probably could use 85. But why? As you mentioned, lower octane can lead to a drop in performance and efficiency. So I'll get slightly worse fuel mileage yet pay less per gallon. In the end it will probably end up costing the same, but with less performance which wouldn't be desirable in the mountainous territory that I drive in. And there would be a slightly greater chance of causing persistent knock which could lead to engine damage. So no, I'm not going to use 85 octane.

Besides, I'm more or less a perfectionist. The manual says to use 87 octane, so I use 87 octane. It also says to use Tier 1 fuel, so I make sure I only buy from stations that sell Tier 1 fuel. I also use Toyota brand engine oil, even though I do my own oil changes. If anyone else wants to do different that's fine, I wouldn't judge them. But it's been my experience that you usually can't go wrong by using what the manufacturer recommends. Don't think I got those 700,000 miles (and still running) out of my VW by using just whatever kind of fluids and parts seemed right at the moment.

 

Yes, the danger is lower. but I wouldn't say it's gone. There are several things that cause knock (well, that cause more heat which causes more knock). And in my situation I have one strike against me and one for me. Higher altitudes will help lower the chances of knock. But long runs up mountains increases it. And I'm not always up that high. My altitude can change between 4,000 and 11,000 feet in a day. And I have driven this car clear down to sea level already, just not on a regular basis.

Yipes! My owner manual also says not to use any more ethanol than E-10, including E-15!​

 

Nothing you can do about E-15 except lobby to stop subsidized farms of the crap. It's coming.

I'm in CO and my Prius is the "mountain goat" as well as the high speed driver along I-70 and I-25. I know exactly the roads you're talking about.

The manual says use 87-octane but if you look into the fine print or just get what it means is that 87 at sea level which also just means "use regular fuel". You aren't at sea level, so you should use "regular fuel". Which depending on where you are fueling up in CO is going to be 81 or 83 or 85. Using 83 or 85 will be fine because at this elevation it acts like the 87-ish stuff. The only time you should fill up with 87 is when you're planning on driving down to the sea level bits. Since the Prius (or your Avalon) can go 500+ miles on a tank, it is not unheard of to drive from 10k ft in Breckenridge where you fill up with 83 out to the plains in Kansas in a single tank where now your 83 is too low. So you would fill up in Breck with the higher stuff so that at the end of the tank and to continue on your journey, you're doing OK.

Colorado is a weird place for vehicles. And most other things.

 

Thanks! That is very informative. I just went up on I-70 from Denver and then through Alma last week. I guess I'll go ahead and try out some 85 and see what it does. I keep a strict watch on my fuel mileage so I'll know if it's making any difference in a bad way. I wonder if there's a rule of thumb or graph for octane at altitudes. It kind of reminds me of when I was driving my VW air-cooled Beetle and had to use different jets at different altitudes.

 

Sorry to derail the thread from annoying diesels to annoying octane numbers. But I found an interesting article on octane, apparently from back in 1987:
Octane Number Requirements of Vehicles at High Altitude

 

Octane is important because we don't want knocking to happen. That happens because of the air and fuel mixture getting too hot, and most of the heat comes from compressing the gaseous mix. This is why high compression engines require higher octane.

At higher elevations, the ambient air pressure is lower. This means there is less air for a given volume than at sea level. So a naturally aspirated engine has less air in its cylinders, plus less gas will be injected to keep the fuel and oxygen ratios right. With fewer molecules in the cylinder, less heat is generated when they are compressed. Thus the risk of knocking, and octane requirements, go down.

Which is inline with what regular octanes are in your area.

 

Yes. Very good observations. I will try some 85 and report back on how it affected fuel mileage. I'm also supposed to get my Techstream kit soon, so assuming I can find out timing advance info, or better yet, knock detection, I'll try to compare those the best I can too and report back.

 

Here's your chance to get your hyper efficient XL1 diesel:

VW XL1 ultra-efficient, ultra-aerodynamic car up for auction - Autoblog

 

So far I've noticed a few differences between the old diesel and the Avalon. In the Avalon hybrid I'm paying over $200 in fuel per month even though I'm getting slightly better than EPA fuel mileage (about 41.7) . Hopefully that will come down a bit by using 85 octane. For the same route it was costing me closer to $150 per month in the diesel to drive. And I was also driving further on a tank in the diesel than in the Avalon too.

Of course that's still an apples to oranges comparison. The VW cost me $600 to purchase and I've only had liability on it, whereas the Avalon cost me $15,000, $9,800 of which I still owe by this third month of ownership with payments of nearly $190 per month. and I have to have full coverage which is over $100 per month. I also changed the transmission fluid, all the air filters (plus an oil change, almost ready for another one), installed a block heater and got a set of 4 used Avalon rims and put 4 new studded snow tires on them. I had also done the same things to the Diesel when I had got it, but the tires and rims were way cheaper and so was the block heater. So far fuel isn't the biggest expense on the Avalon yet, but overall owning the ol' VW diesel is still way cheaper.

But I've also noticed how comfortable the Avalon is than that old diesel. With the diesel I was getting a terrible pain in the hip. Now that pain is nearly gone in the Avalon. And it's also much easier to converse in the Avalon than the diesel, and the radio actually works. Plus the roof doesn't leak like it does on my diesel. And man! The Avalon feels like a race car! I can actually go up any mountain pass at the speed limit (or faster if I wanted to.) The Avalon also has a ton of trunk space. And I was able to hide my tire chains, a tow chain, a better tire wrench and a set of jumper cables within the tray above the spare tire. All I have in the trunk space that's mine and not my wife's is a 12V air compressor.

With the diesel it was hard not to, or should I say necessary to make big clouds of black ash as I went up mountain passes. But the Avalon of course doesn't do this. I do wonder, however, how much the exhaust is affected by the steep grades around here. I can't stand to drive behind gasoline cars going up hills because in most of them the drivers feel like they have to keep them floored, which makes for a rotten exhaust smell even on the newest of cars. I generally am easy going up hills, so hopefully I'm not provoking too often high power enrichment and EGR throttling which cause the overwhelming of the catalytic converter and thus those smells.

All in all, I'm happy with our Avalon Hybrid, and don't plan on going back to a diesel any time soon. Yes it costs more. But it keeps the wife happy, and that's all that really matters. I at times feel like I should have gone for a PIP or a new Prime, especially with Colorado's hefty tax credit and the fact I have a non-used J1772 40A 240V EV charging station on my house. But I really need 5 seats and a spare tire. And after looking at several Prii and the Avalon, both my wife and I felt the Avalon was what we wanted. I do toy with the idea of adding a bit more battery to it and making it a plug-in hybrid some day though. (I've also toyed with the idea of doing a CNG conversion.) But then again, I don't think that would be a good idea at this point. My main mission is to just make the car last. The longer it lasts the better it will be economically.

 

It's too early to tell if this was just a fluke, but on my first tank of 85 octane I got 48.0 mpg instead of the usual 42.5. It was also 30 cents cheaper per gallon.

 

Ha, your buying that lawnmower gas. We've got it at a couple stations here where I live and I've put in in the car once by mistake. Just so you know your going to have half this forum up in arms because your burning 85 octane. LOL

It sure isn't as cheap as what your paying though. The "cheap" gas here is the 15% ethanol mix. (Which is what I use)

 

Well, I'm just testing it to see if it will work here at my altitude, because that's what they sell here as regular. We don't have E15 fuel yet, but I do know that my manual says not to use that either.

I sure had it cheap when I drove my diesel. 55mpg or better with the price of diesel usually cheaper than 87 octane.

EDIT:
I just redid the numbers and actually got 41.1mpg.

 

Diesel's running higher than premium around here.

 

According to google, the highest point in Indiana where your location says you are is 1257ft. The absolute lowest altitude in Colorado is almost 2.6x your highest, at 3315ft above sea level, and a mean of almost 7000ft above sea level. It is not "lawn mower gas" up here, it is regular to mid level.

 

Each place is different. Here it seems that when prices change diesel changes up first or down last. When that happens it is more expensive for a few days. But after a few days gasoline prices usually catch up. And when they do, then diesel is usually around the price of mid-grade (which is 87 octane here, the same octane recommended in the owner's manual). Sometimes it's higher and sometimes it's lower. Right now diesel here in town is $3.299 compared to our mid-grade 87 octane at $3.249. So it's 5 cents more expensive right now. But if my memory serves me correctly, gasoline just got cheaper by about 5 cents a few days ago. So they were the same price, and in a few days diesel may come down to the price of mid-grade again. Also, diesel is 20 cents cheaper than premium (91 octane) at the moment.


Gunnison Gas Prices - Find Cheap Premium Gas Prices in Gunnison, Colorado

 

Yeah, he replied saying the same thing in a post or two earlier than yours. Once he said that I kinda figured it must have something to do with the altitude out there.

Around here though - it's known as lawn mower gas but it's rarely found anymore.

 

Most lawn mowers and power equipment actually call for midgrade or higher these days.

 

That's true.