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The trick to maximizing fuel efficiency on the highway is to minimize the variance in throttle opening and thus fuel use. (Shane Hart/Getty Images/iStockphoto)
The trick to maximizing fuel efficiency on the highway is to minimize the variance in throttle opening and thus fuel use. (Shane Hart/Getty Images/iStockphoto)

You & Your Car

Does cruise control help gas mileage? Add to ...

Can you help me settle a debate? Is it or is it not more fuel-efficient to use cruise control? – Ward

It probably is. I say that because there are qualifiers. It depends on the driver and the cruise control systems.

The trick to maximizing fuel efficiency on the highway is to minimize the variance in throttle opening and thus fuel use. A driver who is paying strict attention and looking far down the road can anticipate issues that will require a change in throttle opening and make gradual and slight adjustments accordingly. A hill will require more throttle while a traffic situation may create a need for a lower speed. A cruise control system cannot see hills and traffic flow. It will maintain speed until the driver steps on the brakes and use the necessary throttle and fuel to resume that speed when required.

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But there is a vast difference in cruise control systems. My regular test route contains a variety of elevation changes, some pretty steep and sustained. I have seen cruise control systems that allow a variance of more than 10 per cent, allowing the speed to drop that much before taking corrective action. When this does occur, it requires a pretty significant dose of throttle to get back to speed. Other systems will tackle these same grades allowing no more than a 1 per cent change in speed.

Another issue in this respect is the number of gears in an automatic transmission. At highway speeds, the first thing a cruise control system will do when faced with a hill is unlock the converter, allowing the engine to rev up and generate more power. If that is not enough, it will tell the transmission to shift to a lower gear. If there are eight speeds in the transmission that might mean a 1,000-rpm increase in engine speed. If there are only four speeds, that might mean a 2,500 or greater increase in engine revs and fuel use.

Generally speaking at highway speeds, on relatively flat roads with little change in traffic speed, cruise control will result in better fuel mileage.

Ethanol in gas

My neighbour tells me the ethanol in today’s fuel ruined his chain saw and lawn mower engines. Can it harm my car engine? – Jim in Windsor

No, it will not.

Today’s passenger vehicle engines are developed around fuel that contain ethanol. However, there is no question the federal requirement that gasoline sold in Canada contain 5 per cent ethanol has caused difficulties for small engines such as those used in lawn mowers, weed whackers, etc.

The Canadian requirement is lower than the 10 per cent in the U.S., which is moving to 15 per cent. At the 5 per cent level I doubt it is creating the problems your neighbour reports, but at 15 per cent there might be issues, particularly with engines left unused for lengthy periods of time since ethanol contains more moisture, which can lead to rust and at high concentrations dissolve some plastic parts.

There is a growing market for, and supply of, boutique ethanol-free fuels formulated specifically for power equipment whether used straight or mixed with oil for two-cycle engines. Expensive though at $2.50/litre or more.

But you need not go that route with your little engines. Buy gasoline for these appliances in small quantities so it does not sit around long. Buy premium gasoline as it has more additives to burn cleaners and use a fuel stabilizer. Don’t look for this problem to go away. Ethanol produces less energy per unit than gasoline, so is detrimental to fuel mileage, but it is cheaper than gasoline so adding more than required is one way for refiners to pad their profits.

Starting old engine

My grandfather passed away recently and I have the opportunity to get his 1968 Impala. There is nothing special about the car other than then memories attached to the summer visits to my grandparents and the drives in that big old boat. The car appears to be in good condition with no rust, but it has not been used or driven for many years and I worry about the engine. Will it have been damaged by sitting for so long? What steps should I take before attempting to start it? – Paul in Regina

Many of the engine’s internal metal surfaces may be stuck together because the oil will have broken down by now.

Step one would be to drain the old oil and replace it with a high-quality one designed for high-mileage engines.

Having done that, you can try turning the engine over by hand with a wrench at the end of the crankshaft pulley. If it moves, you can remove the distributor and use an electric drill and dummy distributor shaft to drive the oil pump and circulate the new oil through the engine. This will also pump up the hydraulic lifters.

But that is only the beginning! Now you will have to deal with removing all the old gas, cleaning and rebuilding the affected components before starting the engine. Make sure you also replace the transmission fluid before attempting to move the vehicle.

Then comes the biggest problem – various leaks as the old seals and gaskets might have dried out. The degree to which you will be affected by any or all of this will vary, but at some point a rebuilt engine or transmission might be a wise move.

globedrive@globeandmail.com

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