Gas mileage questions for gearheads

[Nords]

Our local CATV company sponsors a show called "Go Green Hawaii" profiling local initiatives like solar, biodiesel, & energy-saving lifestyles. It's light on facts & details, assuming that most viewers can't even spell PV and showing lots of human-interest shots & pretty pictures.

Spouse was watching an episode on maximizing a car's gas mileage. Unfortunately the show garbled its terminology and failed to critically evaluate the concepts behind the recommendations. Rather than get all nuclear on my spouse's reporting (I know how well that works) I thought I'd throw these questions out to the board in order to learn the historical perspective. Maybe the show got their facts wrong but there could be a nugget of truth to be extracted from their claims.

So while I question their credibility, my curiosity is piqued by the following putative gas-saving tips:

1. Put a 1000 CCA battery in your car. The show claimed that a higher voltage ("better spark") would be delivered to the spark plugs, although they didn't seem to appreciate the function of the alternator or the primary coil. (Assuming cars still use primary coils.) Maybe they think that less gas is wasted during engine starts.

2. Use a high-flow-rate air filter. "KNN" brand was specifically mentioned. It would seem to me that a higher flow rate would just allow more/bigger contaminant particles to get through the system.

3. Use low-resistance sparkplugs. Autolite was recommended, although again I'm not sure what the advantage of a lower resistance would be. I don't think hydrocarbons care about the resistance quality of the spark-- or maybe low-resistance plugs produce a spark more quickly during the combustion cycle?

4. Synthetic engine oil (Royal Purple). I think this recommendation has been kicking around for decades but I can't recall whether any unbiased double-blind trials ever found any credibility to the claim. Then there's the issue of whether the gas savings really pay for the oil or whether the true savings is in the engine's longer lifespan. Considering that most of the rest of our cars have failed long before the engines, I don't think I care about better engine longevity.

5. Fully-inflated tires. Less rolling resistance, I guess, although I don't know how that affects tread wear (and tire life, which could raise the replacement costs).

6. Put down your beverages before reading this next one. Remember, I'm just reporting the show's claims here, so don't blame me for spewing liquids on your keyboards/monitors.

"Put mothballs in your gas tank." (I can't believe that the show's lawyers let this one go by.) The specific recommendation was five mothballs per gallon (not four, not six, and not even 5.5!). The theory is that the mothball's naphthalene boosts the fuel's octane rating, thus raising mileage. 10 minutes of research informed me that mothballs don't necessarily contain naphthalene anymore, and of course there's the issue of what the remaining crap in the mothballs would do to fuel pumps, fuel filters, and fuel injectors. Ed, I'm sure your fellow Chem Es would enjoy testing this one on an industrial-sized engine...

Perhaps a better question would be-- short of nitrous oxide, is there a fuel additive that boosts gas mileage enough to make it worth the expense?

I hope you enjoyed reading this post as much as I enjoyed writing it. I don't the TV show has much left to offer, especially when all the Nuuanu aunties start calling in to learn how to extract the mothball sludge from their gas tanks.

[cute fuzzy bunny]

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Originally Posted by Nords 1. Put a 1000 CCA battery in your car. The show claimed that a higher voltage ("better spark") would be delivered to the spark plugs, although they didn't seem to appreciate the function of the alternator or the primary coil. (Assuming cars still use primary coils.) Maybe they think that less gas is wasted during engine starts.

No. The CCA value of a battery has absolutely nothing to do with how "hot" a spark you get. Changing your spark plugs or coils might, but if you're using the recommended plugs and they're in good condition, you will likely get no significant improvement that offsets the cost of changing out whats in there.

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2. Use a high-flow-rate air filter. "KNN" brand was specifically mentioned. It would seem to me that a higher flow rate would just allow more/bigger contaminant particles to get through the system.

Somewhat. An aftermarket filter that has more filter area, usually which comes in its own housing, may slightly increase air flow. And cost more than the gas savings. A lot of KNN filters, particularly the oiled variety, can have nice airflow when they're clean and freshly oiled. Two days later, maybe not so much.

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3. Use low-resistance sparkplugs. Autolite was recommended, although again I'm not sure what the advantage of a lower resistance would be. I don't think hydrocarbons care about the resistance quality of the spark-- or maybe low-resistance plugs produce a spark more quickly during the combustion cycle?

No again...see #1. A sparks a spark.

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4. Synthetic engine oil (Royal Purple). I think this recommendation has been kicking around for decades but I can't recall whether any unbiased double-blind trials ever found any credibility to the claim. Then there's the issue of whether the gas savings really pay for the oil or whether the true savings is in the engine's longer lifespan. Considering that most of the rest of our cars have failed long before the engines, I don't think I care about better engine longevity.

Somewhat. Again, you're not going to offset the cost of the oil with the gas savings. If you can get a synth change for the price of a regular change, its worth it.

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5. Fully-inflated tires. Less rolling resistance, I guess, although I don't know how that affects tread wear (and tire life, which could raise the replacement costs).

Fully, yes. Overinflated, you'll wear the center of the tire too fast, make a lot of tire noise, have a harder ride...but you might squeeze a half mpg out. Underinflated tires are bad...excessive wear on the edges, heat buildup/blowout potential, and worse handling/mileage.

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6. Put down your beverages before reading this next one. Remember, I'm just reporting the show's claims here, so don't blame me for spewing liquids on your keyboards/monitors. "Put mothballs in your gas tank." (I can't believe that the show's lawyers let this one go by.) The specific recommendation was five mothballs per gallon (not four, not six, and not even 5.5!). The theory is that the mothball's naphthalene boosts the fuel's octane rating, thus raising mileage. 10 minutes of research informed me that mothballs don't necessarily contain naphthalene anymore, and of course there's the issue of what the remaining crap in the mothballs would do to fuel pumps, fuel filters, and fuel injectors. Ed, I'm sure your fellow Chem Es would enjoy testing this one on an industrial-sized engine...

NO! This does not work and probably never worked. It will however damage your engine. At this point, i've determined that the show producer never had a lawyer look over their recommendations.

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Perhaps a better question would be-- short of nitrous oxide, is there a fuel additive that boosts gas mileage enough to make it worth the expense?

NO!

[travelover]

This is pretty bad advice, except for inflate your tires.

The higher Cold Cranking Amps battery has more amp capacity, not voltage, but that doesn't make a difference in the firing voltage at the plugs.

Modern cars have a mass flow meter to adjust the fuel ratio, so changing the restriction of the air filter doesn't give better mileage. Changing a dirty air filter is a good idea, though.

The spark plugs recommended by the manufacturer are optimized for economy and emissions. I'd have to see some data on this one

Synthetic oil may help mileage a tiny bit, as it allows for less pumping losses if you can use a lower viscosity with synthetic.

Mothballs? Cover the keyboard!

[Webzter]

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Originally Posted by cute fuzzy bunny At this point, i've determined that the show producer never had a lawyer look over their recommendations.

I heard that they were going to but the lawyer's car blew up on the way to the meeting because he used 6 mothballs instead of 5.

[packrat44]

Nords,

The answers from CFB are all correct as stated.

My background includes includes a degree in Mechanical Engineering and have owned an auto repair shop many years ago. I still work on my hot rods - 1940 Ford coupe (supercharged Chevy); 1936 Ford 5-window coupe (supercharged, bored and stroked early Olds); 1942 Willys Jeep; 1929 Model A (to become a ratrod) - along with my daily drivers.

[Sam]

1. Disagree

2. Agree. But have the same concern about contaminant getting through. More air is alway better, which is the basic idea behind super charge and turbo.

3. Don't know. But doubt it.

4. Agree, because synthetic oil is usually thinner. However, the saving is very insignificant (0.1 mpg?). That's said, I'm a fan of synthetic (Mobil 1, and now Mobil 1 Extended Life) since 1991, not because of improved gas mileage, not because of improved engine longevity, but because of time saving. With Mobil 1, 10K. 15K with Mobil 1 Extended life.

5) Agree, but will never practice. The higher the pressure, the less the contact surface, thus the less resistance. But at the cost of uneven wear, not a chance. I use the pressure recommended by the car manufacturer.

6) Very entertaining.

7) Bonus: Certain people claim that rolling down the windows instead of using the A/C also save gas. Tests have done to show that there is no difference. The additional wind drag cause by the open window negates the additional power use by the A/C. Now if you have the A/C on and the windows opened, that would be a different story.

[CCdaCE]

2. Incidentally, it's K & N air filters. I have one in our Subaru. Didn't seem to make much difference as far as mileage (1/2 MPG?) just "seemed" to increase horsepower. Obviously, I didn't dyno. test it to see if I got a 3-5 HP boost. I doubt a human could tell a 2% increase in HP, either.

Disregard all of that. The best part about this filter is that they're supposed to be good for 30-50k miles. I've read they last up to 100k if you drive in "clean" areas, without needing to clean them. I think that'd be pushing it. See their FAQ's.

Instead of a paper looking air filter, they look like a screen door screen with thin cotton over it which is oiled. More air can pass through easier, and supposedly the oil collects all the fine particles. Again, see the FAQ link.

So, instead of spending $20 to change it it every 10k miles, you can blow $30-60 and go 50k miles. Obviously, the cost/benefit analysis will vary with manuf. recommendations for changing your air filter and how much your model of K & N would cost. I think mine was $40-ish? It's been 6 years. Then, the "re-oil" kit is like $10-12, last time I checked.

-CC

[travelover]

The K&N filters are designed to increase airflow for a performance increase, not necessarily a fuel economy increase. They hint that their filters may improve mileage on their website, but the thrust is toward performance.

K&N High Performance Air Filters, Oil Filters, & Cold Air Intakes - Official K&N Engineering Site

[Nords]

Yeah, I was afraid that this would be mostly entertainment value. I'm wondering if it was a gag show and they're going to come clean next week. Assuming they have any money left after legal expenses.

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Originally Posted by Sam 4. Agree, because synthetic oil is usually thinner. However, the saving is very insignificant (0.1 mpg?). That's said, I'm a fan of synthetic (Mobil 1, and now Mobil 1 Extended Life) since 1991, not because of improved gas mileage, not because of improved engine longevity, but because of time saving. With Mobil 1, 10K. 15K with Mobil 1 Extended life.

I'm intrigued. We only drive 3000-4000 miles/year so I end up changing the oil every six months just to get out the water, acids, & assorted gunk. OTOH I'd be happy to be able to stretch that out to 12-18 months. Would either of those synthetics allow me to blow off stretch out the interval between oil changes? Or would that just give the same amount of water, acids, & assorted gunk a longer time to mess things up?

[calmloki]

Are you kidding me??! They didn't tout the virtues of a virtues of a hydro-catalyzed electron directed fuel stream? Mounting two of our cow magnets in the right location could be shown to deliver 50 more HP from a 1998 Le Baron, with attendant fuel economy boost of 27.4%. What, no EBray intake Turbolyzer? No battery powered turbocharger? Sounds to me like their research staff wasn't really working. BTW, most of the Bimmer groups i'm on feel the K&N sounds like more horsepower, but can't show more, but can show greater particulates being passed through.

[TromboneAl]

I remember some article that said "If there were some additive that improved gas mileage, don't you think the oil companies would have added that already?"

We have some higher-quality tires with a max pressure rating of 44 psi. According to the tire store, they can be safely inflated to any value from about 35 to 44 psi. We get a few MPG better at that 44 level, and I like the ride fine.

It's hard to experiment, since we can see a variation of 4 MPG or more from one fill-up to the next. I think the variation comes from who did more driving (one of us isn't as smooth as the other), exactly when the gas pump shut off, where we drove, surfboard rack on/off, etc.

[Bigritchie]

First thing I do when I get a new car.......buy a KNN filter.

I LOVE them. More power, better fuel, and re-usable.

I was amazed the first time I slapped a KNN into a corvette.

I can remember when I lived in Okinawa, that gas was 8-9 bucks a gallon, and this was back when we had 90 cent gallon here, and I always wondered how in the world they could afford it, until I found out all the cars got like 50+ Mpg.

Hopefully here in America the car companies will get off the oil companies nipples, and start making engines that get much better gas mileage.

[Sam]

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Originally Posted by Nords I'm intrigued. We only drive 3000-4000 miles/year so I end up changing the oil every six months just to get out the water, acids, & assorted gunk. OTOH I'd be happy to be able to stretch that out to 12-18 months. Would either of those synthetics allow me to blow off stretch out the interval between oil changes? Or would that just give the same amount of water, acids, & assorted gunk a longer time to mess things up?

I think it's safe for up to one year. On some of my cars, I let it slide a little longer. Bottom line, I would not worry at all if it's 12 months or less. The advantage of synthetic is that it does not break down as quick as the natural one.

Edit to add: I just looked at the label on Mobil 1 Extended Performance (not Extended Life, I used the wrong term before), and it said:

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Protection Guaranteed: Proven protection of critical engine parts from lubricant related failure for 15,000 miles or one year, whichever comes first.

[Sam]

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Originally Posted by TromboneAl It's hard to experiment,

A more scientific way to confirm the benefit of higher pressure tires is to run a coasting test. On a same stretch of road, preferably downhill, bring the vehicle up to a certain speed, switch the transmission into neutral, and clock to see how long it takes to get down to a certain lower speed.