Octane 101

Is premium fuel worth the premium price?
By Nina Russin

Photo courtesy of Ford Motor Company

In our supersized society, we tend to assume that more is better. If a big gulp is better than a small gulp, then premium fuel must be better than regular unleaded. Many drivers believe that octane is a performance enhancer: that’s a misconception. Octane’s purpose is to prevent engine damage that can occur due to pre-ignition or detonation, or what most people call “engine knock.”

Internal combustion engines create power through a series of controlled explosions called combustion. Here’s how it works: a fuel injector sprays gasoline into the engine cylinder, and mixes with air entering through the intake valve. The intake and exhaust valves close, sealing off the cylinder. The piston moves down in the cylinder, compressing the vaporized gasoline to make it more volatile.

A spark plug fires, igniting the mixture. The explosion pushes the piston back up in the cylinder. As each piston moves up in the engine cylinder, it creates energy to spin the crankshaft: the power that eventually finds its way to the wheels. The spent fuel exits the engine cylinders through the exhaust valves and makes its way to the tailpipe.

In order for the engine to work properly, the fuel must only ignite when the spark plug fires. But because gasoline is so flammable, explosions can occur in the engine cylinders at other times as well.

Internal combustion engines are inherently inefficient: some gasoline passes through the cylinders without burning. If this gas vapor auto-ignites after the spark plug fires, the result is detonation. Detonation can burn pistons, shatter spark plugs, or even crack the engine’s cylinder heads.

Pre-ignition is caused by a hot spot in the combustion chamber that ignites the fuel mixture before the spark plug fires. It sound like pinging or knocking, and over time, can cause similar damage to detonation.

Octane reduces gasoline’s tendency to auto-ignite, protecting the engine against detonation or pre-ignition. Manufacturers will recommend the minimum amount of octane necessary to protect the engine against damage. High compression engines tend to need more octane, because they are more susceptible to detonation. Supercharging, which uses a blower to increase the volume of air moving through the engine, can also raise the car’s octane requirements.

Octane requirements increase when vehicle weight goes up significantly: for example, when a truck is towing a large trailer. Extreme heat can make an engine more likely to detonate than moist, cooler air, raising the engine’s need for octane.

The bottom line is this: don’t use gasoline with a lower octane rating than the manufacturer recommends because the engine may not run as efficiently, and the likelihood of damage from detonation or pre-ignition increases. On the other hand, using premium fuel when the manufacturer recommends regular is a waste of money.

Why diesel fuel doesn’t have octane

Diesel is a heavier grade of fuel than gasoline. Diesel engines don’t have spark plugs because they can’t  ignite the fuel. Instead, the engine uses extreme compression to create combustion.

Pistons in the diesel engine compress air in the cylinders to make it hotter. When an injector sprays diesel fuel an engine cylinder, the air inside is hot enough to make the fuel burn and expand.  The burning fuel creates enough power to move the piston back and spin the crankshaft.

The ticking sound we hear when a diesel car is running is detonation: it’s a common occurrence in diesel engines. So engineers use components robust enough to withstand the stress of random explosions inside the cylinders.

Detergent additives

Many gasolines have detergent additives to prevent deposits from forming inside the engine. Fuel injector tips can become clogged over time with paraffin and dirt. Clogged fuel injectors can’t deliver enough fuel to the engine cylinders and fuel economy suffers.

While detergent additives can do a good job of preventing dirt from building up on the injector tips, they are less successful at removing deposits that have already accumulated. Fuel injector cleaners that go into the gas tank are equally ineffective: they simply aren’t strong enough to do the job.

Any fluid strong enough to clean the injector tips is also strong enough to do damage to the fuel lines that run to and from the fuel rails. That’s why technicians inject these materials directly into the fuel rails, after they block the fuel lines off.

Some manufacturers recommend against using these caustic injector cleaners, because they can cause damage to the injector tips. The best way to clean these injectors is to remove them and clean them ultrasonically: a job best done by a qualified technician.

E85

Some new cars, also called flex-fuel vehicles, are made to be E85 compatible. E85 is a gasoline mixture that contains up to eighty-five percent ethanol by volume. Ethanol, which is produced from corn, is a renewable fuel. Using renewable fuel reduces our dependency on oil, which as we all know is a limited resource.

The bad news is that using E85 reduces a car’s fuel economy. E85 is also more expensive than conventional gasoline. So drivers who need to stretch their gasoline dollars should think twice before filling up with E85.

Hot gas versus cool gas

Like any other liquid, gasoline expands when it gets hot. Gasoline density effects power: the denser the liquid, the more power it can create. Therefore, gasoline that is warm due to higher ambient temperatures will contain less effective power than cool gasoline. The debate of warm versus cool gas has been the subject of recent media attention, with arguments on both sides. While some experts claim that ambient temperatures have a significant effect on underground tanks, others claim that the tanks are relatively temperature proof.

Does it pay to fill up the tank during cooler times of the day: in the early morning or at night? The answer is ‘yes,’ but not necessarily because of the gasoline temperature. The hotter the ambient temperature, the more likely gasoline is to escape around the neck of the fuel tank in vapor form. That’s because gasoline vaporizes at very low temperatures: much lower than ambient air.

Modern fueling stations have a collar around the filler nozzle to minimize evaporative emissions. In addition, cars have specially designed as caps that seal off the neck of the fuel tank, to minimize pollution from gasoline fumes. Filling up in the cooler weather minimizes evaporative emissions, causing less pollution and probably saving some money as well.

2008 Toyota Highlander Limited 4X4

Toyota’s seven-seat crossover ventures off road.
By Nina Russin

2008 Toyota Highlander

I’m driving south through Oak Creek Canyon, a narrow passage formed by the waterway connecting Sedona and Flagstaff, Arizona. It’s an appropriate place to drive the new Toyota Highlander: a mid-sized crossover vehicle that builds on the original formula with new off-road technology.

The first Highlander that debuted in 2001 was the urban counterpart to the Toyota 4Runner. Whereas the truck-based 4Runner appealed to outdoors enthusiasts with extreme off-road capability, the Highlander offered buyers enhanced passenger and cargo capability, but with a car-like ride.

The new model that rolled out last year shares chassis components with the Camry and Avalon sedans. Full-time four-wheel drive with hill-start assist and downhill descent control  allows the new Highlander to traverse moderate off-road trails with aplomb.

The test car is the upscale Limited grade: one of three available trim levels. A 270-horsepower engine and five-speed automatic transmission provide ample power while maintaining reasonably good gas mileage: about 20 miles-per-gallon on average. A hybrid version of the car averages 26 miles-per-gallon, thanks to power enhancement from three electric motors.

A price increase that took effect the beginning of May boosts the car’s $34,150 MSRP by $200, and adds $40 to the $645 destination charge. Options include a navigation package ($2505) that includes a JBL audio system upgrade, with pre-wiring for satellite radio, MP3 and Bluetooth capability, power rear door ($400), rear air conditioning system ($585), power sunroof ($850), rear spoiler ($200), and car mats ($275).

Touring the red rocks

Memorial Day weekend in Sedona is the end of peak tourist season. Highway 89A- the two-lane road that runs through Oak Creek Canyon and continues south towards Prescott, is packed with cars. Though travelers can make better time on the interstate, the red rock formations surrounding the two-lane highway make that drive irresistible.

There is a second route through Oak Creek: a graded dirt road that hugs the canyon wall between Sedona and Munds Park, just south of Flagstaff. Recent rains have made the road a little rougher than normal. But it’s nothing the Highlander can’t handle.

Up above the traffic, the real spirit of the canyon springs to life. An unusual cold snap has extended the life of spring flowers. Deer occasionally peek out between the Ponderosa pines. And the scent of those pine trees is everywhere. Thanks to the rains, the normally dusty route is relatively dust free.

Schnebly Hill is one of many graded dirt roads in and around Sedona. While most people prefer to stay on pavement, the fire roads are a quieter, more scenic way to get around. Visitors planning to run, hike or mountain bike can count of having to travel some of the fire roads to get to the nicer trails.

I won’t say that it’s impossible to travel these roads in a car, but there are sections where piles of tea kettles or deep sand compromise traction. The Highlander’s four-wheel drive system is the perfect fix, since it automatically sends engine torque to the wheels with the most traction.

Ample ground clearance and short overhangs prevent the underbody from getting hung up on hills. The four-wheel drive Highlander can wade through several inches of water without losing traction or damaging the drivetrain. I tried it myself just to make sure.

While the ’08 Highlander has more off-road features than the outgoing model, it lacks the durability that makes the 4Runner capable of handling extreme off-road terrain. I wouldn’t tackle the Rubicon Trail in a Highlander: that’s 4Runner territory.

On the other hand, the ’08 Highlander has enough towing capacity to meet our ALV minimum standards. Both second and third row seats fold out of the way to create a long cargo floor for loading in bicycles and other oversize items. Roof rails are standard on the Limited grade, and crossbars are a factory-installed option ($229).

Plenty of power for the open road

The trip up interstate 17 is my favorite way to test a car’s power. The road climbs about 5500 feet between Phoenix and Flagstaff. Not only does the Highlander have enough power to pass slower vehicles on steep sections of the ascent, but the transmission does a minimum downshifting. Fuel economy on the highway averages 22 miles per gallon: a touch below the 23 mpg EPA estimates.

The Limited grade comes with standard nineteen-inch wheels, and a fully independent suspension that provides a firm but compliant ride. Visibility is good all the way around the car.

Toyota prides itself on quiet interiors: the Highlander is no exception. Engineers increased insulation around the instrument panel on the new model and revised the engine mounts to further reduce noise intrusion to the passenger compartment.

Four-wheel disc brakes with standard antilock braking are firm and linear without being grabby. Steering assist is ample for low-speed driving. At high speeds there is less assist for  a positive on-center feel.

Spacious interior

Designers made the ’08 model larger than the car it replaces in every dimension, giving second and third-row passengers more head, leg and hip room. Both first and second-row seats move fore and aft to accommodate tall passengers.

There are plenty of storage areas around the first two rows for holding maps and small electronic devices. I was a little disappointed that the glove box and center console bin are too small to hold small packs, since I like lockable storage at the trailhead. But a tonneau cover in back conceals items in the cargo area from prying eyes.

All four doors have map pockets and bottle holders, and there are plenty of cupholders for all three rows of passengers. Two power outlets in front and one in the cargo area recharge portable electronic devices.

A standard tilt and telescoping steering wheel allows smaller drivers to maintain a safe distance from the front airbag. Redundant audio controls and cruise control buttons on the steering wheel reduce driver distraction.

The center stack is logically laid out, with temperature controls at the bottom, and audio controls surrounding a central information screen that also displays a wide angle camera view to the rear when the car is in reverse. The rear backup system makes it much easier to back into tight parking spaces, and displays items that would normally fall below the driver’s sight line.

Up above, a conversation mirror flips down, so parents can keep an eye on kids in the second row. The optional moonroof lets plenty of ambient light into the back of the car. I enjoyed having it open in the north country, so I could see the pine trees towering overhead.

Two paths to the third row

A new second-row seat design makes it easier for third-row passengers to get in and out of the car. The middle seat is removable: it stows behind the front-row center console. Since the Highlander has rather thick C pillars and large wheel arches, access and egress via the rear doors is limited.  Though they aren’t as spacious as the second-row seats, the two, third-row seats are big enough to hold adults.

A standard power tailgate eliminates fumbling with the keys, making it much easier to load up the cargo area. With the third row seats folded flat, the Highlander easily meets our bicycle friendly standards.

Standard safety features include antilock brakes, vehicle stability and traction control, front, side, side curtain and driver’s knee airbags, front headrest restraints and a tire pressure monitoring system.

The 2008 Highlander is currently on display at Toyota dealerships nationwide.

Likes: A mid-sized crossover vehicle with a versatile interior, standard roof rails, and the ability to handle moderate off-road trails.

Dislikes: Large C pillar and rear wheel arches limit egress from the third row seats. Cargo and floor mats should be standard equipment on a vehicle at this price.

Quick facts:

Make: Toyota
Model: Highlander 4X4 Limited
Year: 2008
Base price: $34,150
As tested: $40,674
Horsepower: 270 Hp @ 6200 rpm
Torque: 248 lbs.-ft @4700 rpm
Zero-to-sixty: N/A
Bicycle friendly: Yes
Off-road: Yes
Towing: Yes
Antilock brakes: Standard
Side curtain airbags: Standard
First aid kit: Not available
Fuel economy: 17/23 mpg city/highway
Comments: A recent price increase raised the Highlander’s MSRP by $200, and added $40 to the delivery charge.