[Frosted Glass]

This is a question about engines and I am seeking advice from the collective wisdom of the group. Which gasoline is the best choice and why? Here is my situation. I have a 2012 FF with 24,000 miles. In my area by law ALL the gasoline must have ethanol. Everything I have seen has 10%. The choices are 91, 89, 87 octane. The manual says my car is designed "to use regular gas with a rating of 87. Using gas below 87 is not recommended. Premium fuel will provide improved performance." When I use premium I perceive my car having more power and gaining at least 2 mpg improvement on the in dash calculator. When I use 89 I still observe some increase in power and I save a few pennies. However when I use that octane when I go up an incline under light acceleration I hear a slight engine grumble. Is this knocking? The manual says "do not be concerned if your engine sometimes knocks lightly. However if it knocks heavily under most driving conditions while using the fuel with the recommended octane rating see your authorized dealer to prevent any engine damage. On this board people have said you can use premium because the computer brain advances the spark properly. I have also read manuals for the 2013 and 2014 do not include the sentence "Premium fuel will improve performance". If this is true, why the change? Should I just stick with 87 octane? Or should I use 91 octane and skip the in-between rating of 89 because it is confusing the computer brain.

 

[wv rider]

Your ECU should compensate for the use of those grades of fuel. Ethanol generally has a higher octane rating than gasoline. So aside from mileage, that isn't really a concern. Also, the fuel components in your car were designed with ethanol use in mind, so no real concern there either. I would run whatever grade of fuel you are comfortable with as any of those grades should work fine for you.

 

[sanford12]

What brand fuel do you use. I use BP 87 octane exclusively and have never had a problem and average 35.5 in a year of driving. Not all but some of the off brand stations the gas ain't real good.

 

[Pennut]

I have also read manuals for the 2013 and 2014 do not include the sentence "Premium fuel will improve performance". If this is true, why the change?

It's an advertising thing most likely. If you were looking for a car and it's MPG was a major concern, would you buy the car that states it takes 87 octane, or a car that says you can use 87 octane, but you will see improved performance with premium?

I use premium only. I see 1-2 mpg in combined driving (which for me is about 15% city & 85% hwy). If I'm driving purely highway such as on road trips, the mileage is the same.

The reason some cars such as turbo's and high compression engines needed the higher octane is related to cylinder temperatures. You compress a gas and it heats up. Higher compression, higher temperature. So higher octane was required so the gas/fuel mixture would not detonate too soon before the cylinder reached top dead center (TDC). That is what a higher octane rating is. The higher the octane rating, the higher the temperature needed to detonate it. It has nothing to do with power. Now, the Focus's engine has variable valve and camshaft timing, so it can compensate for the lower (87) octane. Mostly.

But if you're getting knocking, it sounds like your fuel is either igniting too soon or too late before TDC. Shouldn't really with the variable cam/valves. Are you getting the gas at the same station when you have the problems? I always use some water remover from time to time also. This ethanol gas is junk. Attracts moisture. I started having some rough running when I got gas at a gas station I had been going to for years because I think they got a new fuel provider. Stopped getting gas there and haven't had no problems since.

 

[Frosted Glass]

I use Shell or Mobil gas. These are top tier gasolines. This grumbling does not happen all the time when I go up an incline and so far I have only noticed it with 89 octane. So far I am unable to say for sure it is just one particular brand, but I have a suspicion. All the stations of that one brand close to me are owned by the same family. Maybe those stations have something peculiar to them? Maybe the quality of their gas is problematic sometimes? I don't use BP because when I had my VW and put BP into it the warning light for how clean the engine was running would come on. When I put Shell or Mobil into it the light would go off. Don't know if it is true but VW dealer told me BP was a lower quality gas. Maybe for Ford BP gas is just fine. Maybe there was a problem with that BP station I was using. I will experiment and stop using the one brand I am suspicious of and see if that helps. Maybe the problem is the dealer and his string of gas stations. I just don't want to hurt my engine. I like the extra power but not at the expense of engine repairs.

 

[Frosted Glass]

I know one reply said octane has nothing to do with power. But someone told me octane is a measure of how much energy is in the gasoline and the more energy the better the mpg. It is my perception that my FF is quicker and more forceful when I use premium. I don't have a way of describing it except to say it seems to have more power. That is a good suggestion to use a water remover. Where can I find that and what should I buy? And would that additive invalidate my warrenty?

 

[Kabigon]

This is a question about engines and I am seeking advice from the collective wisdom of the group. Which gasoline is the best choice and why? Here is my situation. I have a 2012 FF with 24,000 miles. In my area by law ALL the gasoline must have ethanol. Everything I have seen has 10%. The choices are 91, 89, 87 octane. The manual says my car is designed "to use regular gas with a rating of 87. Using gas below 87 is not recommended. Premium fuel will provide improved performance." When I use premium I perceive my car having more power and gaining at least 2 mpg improvement on the in dash calculator. When I use 89 I still observe some increase in power and I save a few pennies. However when I use that octane when I go up an incline under light acceleration I hear a slight engine grumble. Is this knocking? The manual says "do not be concerned if your engine sometimes knocks lightly. However if it knocks heavily under most driving conditions while using the fuel with the recommended octane rating see your authorized dealer to prevent any engine damage. On this board people have said you can use premium because the computer brain advances the spark properly. I have also read manuals for the 2013 and 2014 do not include the sentence "Premium fuel will improve performance". If this is true, why the change? Should I just stick with 87 octane? Or should I use 91 octane and skip the in-between rating of 89 because it is confusing the computer brain.

A few thoughts:

1) Don't worry about "confusing" the PCM. It can deal with varying levels of octane.

2) It is highly unlikely that you will ever hear knocking or pinging from your engine because that is exactly what the PCM is trying to prevent.
The knock sensors are far more sensitive than the driver of the car.

3) The PCM will essentially grade the octane level of gasoline in your tank and adjust the ignition timing accordingly.

4) Needless to say, you may get a lot of (highly ignorant) answers from people that don't know anything about the mk3 Focus PCM.

 

[suss6052]

I know one reply said octane has nothing to do with power. But someone told me octane is a measure of how much energy is in the gasoline and the more energy the better the mpg. It is my perception that my FF is quicker and more forceful when I use premium. I don't have a way of describing it except to say it seems to have more power. That is a good suggestion to use a water remover. Where can I find that and what should I buy? And would that additive invalidate my warrenty?

Whomever said that Octane is a measure of energy density doesn't understand what Octane is.

Octane ratings are related to the resistance of a fuel ignition. This has nothing to do with the energy density of the fuel.

Octane rating or octane number is a standard measure of the performance of an engine or aviation fuel. The higher the octane number, the more compression the fuel can withstand before detonating (igniting). In broad terms, fuels with a higher octane rating are used in high performance petrol engines that require higher compression ratios. In contrast, fuels with lower octane numbers (but higher cetane numbers) are ideal for diesel engines, because diesel engines (also referred to as compression-ignition engines) do not compress the fuel but rather compress only air and then inject the fuel into the air heated up by compression. Petrol engines (also referred to as gasoline engines) rely on ignition of air and fuel compressed together as a mixture without ignition, which is then ignited at the end of the compression stroke using spark plugs. Therefore, high compressibility of the fuel matters mainly for petrol engines. Use of petrol (gasoline) with lower octane numbers may lead to the problem of engine knocking.

Octane rating - Wikipedia, the free encyclopedia

Higher octane fuels are beneficial for high compression engines as you can advance the ignition timing further and extract more power or efficiency from the fuel.

Using fuel additives is not recommended, and it is of little benefit.

If the engine is knocking regularly then it would be best to run mid grade or higher to attempt to avoid this.

The Focus is using a very high compression ratio. However thanks to direct injection and variable camshaft timing it is possible to run the car safely and effectively on 87 octane, albeit with reduced performance.

If the car runs fine on 87 octane and you're not concerned about performance just stick to running 87 octane as the car was designed to handle it.

Otherwise use whatever fuel you feel most comfortable with in your area.

 

[wavsine]

Needless to say, you may get a lot of (highly ignorant) answers from people that don't know anything about the mk3 Focus PCM.

Given the choice of hanging out with my buddies with high Stanford-Binet scores or car guys, I will pick car guys every time. They may not have been as fortunate as some to have rich parents put them through college but you would be surprised what you can learn from smart guys who may not be as well educated as you. I learn something new just about every day on this forum and much of that information is gleaned from guys who aren't afraid to get their hands dirty.

 

[Kabigon]

Given the choice of hanging out with my buddies with high Stanford-Binet scores or car guys, I will pick car guys every time. They may not have been as fortunate as some to have rich parents put them through college but you would be surprised what you can learn from smart guys who may not be as well educated as you. I learn something new just about every day on this forum and much of that information is gleaned from guys who aren't afraid to get their hands dirty.

My point was that the OP may read statements such as "If the car was designed to run on 87, premium will not make a difference."

I thoroughly enjoyed hanging out in a Texaco station owned by my friends dad when I was younger and I did learn a lot from people that got their hands dirty.

 

[Tigeo]

Been beaten to death in the premium fuel thread...some good reading for you there. You car is designed (if it is the flex fuel variant) to work off of E85. If it is the non-flex fuel, then E15 max is what you supposed to run. The manual was changed in 2013 to remove the "increased performance w/premium" verbiage...take that as you will. I run regular with no issues. I have also felt the stumble on inclines before and though it *might* be hesitation due to knocking but this is all qualitative so no real data to support that premium actually does anything w/r to it - I have tried. Don't discount placebo w/r to changing fuel types. I have collected data for my highway-only commute that suggest that there is zero difference in mpgs between 87 and 93. Others say that you see an increase in around-town driving. There have been some studies online that suggest that for the direct-injection high-compression engines, that in the summer premium can make a difference. Lots of info, no wrong answers, run what you want.

 

[Frosted Glass]

Most of my driving is city. Rarely get above 50 mph. So maybe that is why I see the increase in mpg with premium gas. The 2 mpg is a real event for me. I have experimented many times with regular and premium fill ups driving the same roads, the same times, in the same weather. Perhaps the grumbling was just a case of poor quality gas. I was concerned about the midlevel range of 89. That maybe the car didn't know how to handle that and I should only put in 91 or 87. But it sounds like the car can figure it out just fine. I think in my case the cost of premium vs regular is a wash due to the mpg factor. I tried to figure it out money wise which way was better but it turned out to be about the same. I prefer the increased power. I feel like I zip around a little faster. I was just trying to maybe save some money by putting in 89. But like I said it is more important not to hurt the engine. Here is another question. If I use premium would that be better because it would be hotter when it explodes and maybe somewhat burn off carbon deposits that may form from direct injection?

 

[suss6052]

Here is another question. If I use premium would that be better because it would be hotter when it explodes and maybe somewhat burn off carbon deposits that may form from direct injection?

Nope, the octane rating has nothing to do with how hot the fuel burns.

The only way to clean carbon deposits other than passing liquid fuel past the intake valves is to remove the head and clean them.

Under normal circumstances direct injection means that no fuel vapors wash over the intake valve to clean it, so it doesn't matter what fuel you use if none of it ever touches the back side of the valve.

 

[Frosted Glass]

This is a very basic question, why did Ford use variable valve and camshaft timing on the FF. I doubt it was so you have a choice of octane at the pump.

 

[wavsine]

This is a very basic question, why did Ford use variable valve and camshaft timing on the FF. I doubt it was so you have a choice of octane at the pump.

Fuel economy, performance, smoother idle, decreased emissions...the list goes on.

If you ever heard a street racer from the '70s set up with a race cam, the idle was really rough because the cam profile was optimized for high rpm. Without the ability to vary the valve timing, you had to choose between a stock cam with a smooth idle or a race cam that shook your teeth out at idle. Variable valve timing gives you the best of both.

 

[suss6052]

Fuel economy, performance, smoother idle, decreased emissions...the list goes on.

If you ever heard a street racer from the '70s set up with a race cam, the idle was really rough because the cam profile was optimized for high rpm. Without the ability to vary the valve timing, you had to choose between a stock cam with a smooth idle or a race cam that shook your teeth out at idle. Variable valve timing gives you the best of both.

^ this

Per the Service manual:

Twin Independent Variable Cam Timing (Ti-VCT) System

The Twin Independent Variable Cam Timing (Ti-VCT) system allows variable control of intake valve closing which optimizes combustion at full load providing improved power and low speed torque (broadening the torque curve) which enables variable valve overlap which provides better fuel economy and emissions and provides optimized cold start operation with improved exhaust emissions.