Using Lower Octane in the Winter

[splinter]

Originally Posted By: kyoo
...So the engine is always cold when it gets driven...

That's 'severe service' of the worst kind imho.

It's easy enough to have its OBD-II monitor and log for knock retard whilst consuming different blends, yes?

 

[camrydriver111]

Originally Posted By: kyoo
well i'd run 89 if anything. i think this is kind of one of those things like - is it recommended to do? not really. is it gonna cause any harm? most likely not. i may give it a shot, why not. i have a hard time believing that, in my particular conditions, the engine would knock anyway, even on 87, let alone 89


This is kinda off-topic but is 89 even worth getting, for any car? Most cars call for either 87 or 91, sometimes 93 as the optimal octane. And if it's blended at the pump who know what ratio it's blended at?

 

[jayg]

You stay out of boost for the most part I would imagine on a cold motor anyway. The ecu will change the maps for you to use 87 but what about when you do want to open it up. The price differnce isn't THAT much if you are just doing a 2 miles commute anyway.


Originally Posted By: ammolab
The time to "drop an octane level" is long interstate drives. Low throttle, high manifold vacuum, steady throttle driving greatly reduces the octane requirement of an engine. Crossing Texas on Interstate 10 is no place to waste 93 Octane gas!


This. And at altitude.

That being said all my vehicles run great on 87 octane and are tuned for it except the bike. At $8 bucks to fill it up, I just use 93.

 

[jayg]

Originally Posted By: camrydriver111
Originally Posted By: kyoo
well i'd run 89 if anything. i think this is kind of one of those things like - is it recommended to do? not really. is it gonna cause any harm? most likely not. i may give it a shot, why not. i have a hard time believing that, in my particular conditions, the engine would knock anyway, even on 87, let alone 89


This is kinda off-topic but is 89 even worth getting, for any car? Most cars call for either 87 or 91, sometimes 93 as the optimal octane. And if it's blended at the pump who know what ratio it's blended at?


Nope. Any car that runs fine on mid will run fine on regular.

I run premium in forced induction or high static compression motors and 87 in everything else.


Sadly, there are a lot of people who think the 93 is "cleaner" than 87 and it will clog up your fuel pump/filter. I've heard that several times from people. What do you think, there is sediment in the cheap gas or something?

 

[camrydriver111]

I can't decide if I should keep putting 91 in my 05 325i or am I just wasting my money. In Canada it comes out to $8-10 difference per 50L tank of gas so it's not insignificant. I know the ECU will adapt to any octane but I wonder how much power you lose (if any).

 

[eljefino]

89 was what regular leaded used to be 30 years ago. They offered it in unleaded at the pumps when the stuff became common and people bought it for some reason, so they kept offering/ blending it. It doesn't take another underground storage tank so why not?

 

[threeputtpar]

I've made the switch over to 89 octane from the E0 91 octane that I was using in the twin turbo A6. It even has an aftermarket tune to up the boost to 16psi. I always make sure it's oil temp is at least above 150F before I get on the gas. I'm not afraid to use all of its power when needed, and I've noticed no difference in its ability to throw me back into the seat.

Once the price difference between regular unleaded and 91 became > $0.60, I didn't feel I was getting that much value. 89 octane is $0.14 more than regular. Most of my miles are commuting at 70mph twice a day, so maybe that makes a difference. It performs just as well around town, so I'm thinking that I've been wasting money all these years on 91 and 93.

 

[kyoo]

Originally Posted By: threeputtpar
I've made the switch over to 89 octane from the E0 91 octane that I was using in the twin turbo A6. It even has an aftermarket tune to up the boost to 16psi. I always make sure it's oil temp is at least above 150F before I get on the gas. I'm not afraid to use all of its power when needed, and I've noticed no difference in its ability to throw me back into the seat.

Once the price difference between regular unleaded and 91 became > $0.60, I didn't feel I was getting that much value. 89 octane is $0.14 more than regular. Most of my miles are commuting at 70mph twice a day, so maybe that makes a difference. It performs just as well around town, so I'm thinking that I've been wasting money all these years on 91 and 93.


interesting - i'd personally never do it on an FI car, but I'm thinking more and more the Mini will be fine. I autox the car regularly, but it's off season now. I "feel" like there's a difference on 91 vs 93, but I think I'll be fine on 89 for regular commutes

 

[jayg]

Originally Posted By: kyoo
Originally Posted By: threeputtpar
I've made the switch over to 89 octane from the E0 91 octane that I was using in the twin turbo A6. It even has an aftermarket tune to up the boost to 16psi. I always make sure it's oil temp is at least above 150F before I get on the gas. I'm not afraid to use all of its power when needed, and I've noticed no difference in its ability to throw me back into the seat.

Once the price difference between regular unleaded and 91 became > $0.60, I didn't feel I was getting that much value. 89 octane is $0.14 more than regular. Most of my miles are commuting at 70mph twice a day, so maybe that makes a difference. It performs just as well around town, so I'm thinking that I've been wasting money all these years on 91 and 93.


interesting - i'd personally never do it on an FI car, but I'm thinking more and more the Mini will be fine. I autox the car regularly, but it's off season now. I "feel" like there's a difference on 91 vs 93, but I think I'll be fine on 89 for regular commutes


Oh I thought your Mini was turbo. I missed that it was a base model, run 87 in and dont worry about a thing.

 

[ofelas]

I don't like the stuff, but 10% ethanol in 87 does run a bit hotter than non eth 91/93.

If all grades of gas have 10% ethanol, its a moot point.

 

[rvt]

Quote:

To preface, my drive to work is roughly 2.5 miles. I drive there and back and then the car sits. So the engine is always cold when it gets driven. Given 30deg and below temperatures, I'm wondering if 89 will actually burn better than 93 under these conditions? I'm obviously not revving, racing, redlining the car on these commutes.


I don't think it will run better with the 89. But I do think with the cold temps, the lack of warmed up engine that the 89 (or 87 for that matter) would have plenty of anti knock capacity. 2.5 miles driving is mostly below normal operating temperature.

 

[camrydriver111]

Originally Posted By: jayg
Oh I thought your Mini was turbo. I missed that it was a base model, run 87 in and dont worry about a thing.


Isn't it high compression 11.1:1?

 

[kyoo]

11:1, is that high?

 

[linksep]

Originally Posted By: timeau
Originally Posted By: kyoo
The air is denser, which makes the air/fuel leaner.

No. Reachier. More oxygen in the same amount of air. To preserve same air/fuel ratio, more fuel is required. That's how cold air intake works.

No, leaner. If you are "running rich" you have used too much fuel for the given amount of air (@21% oxygen) your engine pumps. If you are running lean you have not used enough fuel relative to the amount of air (@21% oxygen) your engine pumps. If it helps you remember: Air is free and fuel costs money; running rich is extra fuel to burn, running lean is having air (oxygen) left over when your (expensive) fuel is gone. It's not more oxygen in the same amount of air, it's more air (@21% oxygen) in the same size cylinder.

Originally Posted By: timeau
Originally Posted By: kyoo
The air is colder, which resists knock better.

These two facts are not related, IMO.

One thing causes knock (preignition), heat. Where can that heat come from? Three places: compression (from compression ratio as well as compression by a turbo or supercharger) this is how a diesel engine runs; a hot-spot in the combustion chamber such as a sharp edge, carbon debris, or the wrong heat-range of spark plug; and the latent heat of air entering the engine. If you run an air/fuel mixture and compression ratio tuned right on the ragged edge of knock with an intake air temp of -20F I can guarantee it will knock running that same air/fuel ratio and compression with an intake air temp of 110F. Furthermore, the specific heat of fuel is many many times more than the specific heat of air meaning the fuel charge cools the pre-combustion air/fuel charge (reducing the chance it will get hot enough to knock).

Originally Posted By: timeau
Originally Posted By: kyoo
can you run a lower octane?

No. The only place where you can use lower octane fuel is mountains.

Why can you run a lower octane in the mountains? Because the air is less dense meaning less heat is generated during compression and that's enough less heat to stave off preignition (knock).

To the OP: Better? Maybe. You would have to scientifically test to find out. An easy beginning way of testing would be to maintain a fuel economy log as well as use some sort of scan tool that can read knock sensor values. If your mileage drops from using mid-grade that is a sign that the ECM is adding fuel to cool the intake charge and reduce knock. Confirmation of that comes from seeing higher knock values from your knock sensor. That in itself does not constitute "better" (except for your wallet), you would then have to prove that high-test actually creates or increases deposits or other unwanted side-effects compared to mid-grade.

Take it for what it's worth (zero because I'm some random ash-hole on the interwebs) but if you don't notice a decrease in fuel economy OR an increase in knock sensor readings then running mid-grade for your driving style is perfectly fine, if not potentially beneficial in some small way.

 

[virginoil]

wrong forum pls move thread

 

[Patman]

You can definitely run lower octane in the winter, and I've done it for many years now in a few different cars. If you hook up a scan tool to your car that shows how much timing the computer needs to pull out to avoid spark knock, you will see that on hotter days it pulls out a lot more than it does on colder days. So as the temperature gets hotter outside the engine needs more octane than it does on colder days. Car manufacturers will base their octane requirement on a worst case scenario, so if they say it needs 91 octane, that would be what the engine needs on the hottest days of summer, but in the coldest part of winter that same engine can get away with a lot less. My wife's BMW calls for 91 octane, but I've been running 89 in it ever since the temperatures have been below 60 degrees here. She doesn't push it hard anyhow, so chances are good that she could even run 89 in warmer temps actually.

 

[camrydriver111]

Quote:
My wife's BMW calls for 91 octane, but I've been running 89 in it ever since the temperatures have been below 60 degrees here. She doesn't push it hard anyhow, so chances are good that she could even run 89 in warmer temps actually.


You could run 87 in a BMW no problem, it says it in the manual you could use 87 if 91 is unavailable. The only issue is how well does it run vs. 91?

On my junker BMW I feel there might be some power loss with 87. When I put 87 in it it felt like the car did before I changed my VANOS seals.

 

[circuitsmith]

I've gone the opposite way.
When the ambient is 100F or above I found that ~89 runs better than the specified 87 in stop and go driving.
So I've put in ~25% premium when a heat wave is coming.