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Automania/Repair and Maintenance

AUTO QUESTIONS AND ANSWERS FOR 1997 WEEK 10

by Bob Hagin

Q. I just bought a '91 Toyota Corolla with the 1.6 liter four cylinder engine. The manual says I can use a 5w-30 or a 10w-30 oil but the 5w-30 is preferred. I live where the winter temperatures are in the 20s and the summer temperatures are in the 90s. Which would be the best for me? I've always used one brand of oil in my cars but I've been told that it's paraffin-based and will create more sludge in my engine than other oils. Is this true? I usually change my oil and oil filter every 3000 miles or three months, whichever comes first. Sometimes I only drive my car a couple of hundred miles in three months. Is it that important to change the oil in three months when I have such low mileage?
C.W. Downeyville, CA

A. It's my personal opinion is that all motor oils are pretty much the same. Consumers Union conducted exhaustive tests on a couple of taxi fleets and after two years, its researchers couldn't find any difference in the wear between cars using different brands of oil. If the your oil containers have the API (American Petroleum Institute) "starburst" on them and they indicate Service SG or better, you're safe in using it. SAE 10w-30 is good from zero degrees to over 100. Sludge isn't much of a factor anymore since engines have been using PCV (positive crankcase ventilation) systems for decades and most blow-by contaminates get pulled out of the oil sump area and burned in the engine. A sludge and contamination problem can crop up if the engine isn't warmed up or used enough to pull out these contaminates. This treatment is called "severe duty" and unless you're taking your Corolla out on non-stop 300 mile trips, your engine qualifies. Airline maintenance crews have the oil they use periodically tested for contaminates. You don't have that luxury so change it and its filter at 3000 miles or every three months.

Q. We have a 1991 Infiniti G20 that has only 62,000 miles on it. Sometimes the engine is hard to start, especially on cold mornings and when it finally does catch, it runs rough for a while when it idles. Once we drive on the highway for a while, the engine seems to settle down. We don't have the car serviced by a dealership since it's very expensive and we are not sure that it's worth it.
K.L. Santa Fe, NM

A. Sometimes you have to bite the bullet and take a car in to have it serviced. Waiting until something falls off or blows up is false economy. If you don't like the way a dealer services your car, ask around and find an independent that has a good reputation. My guess is that you have a spark plug that's shorting out when the weather gets cold and then cleans itself when you drive it around for a while. A technician can catch this pretty quickly on an oscilloscope and the cur could be as simple as a new set of plugs.

Q. A problem has recently developed in my 1986 Oldsmobile 88 sedan. The engine is a V6 3.8 liters and it has nearly 90,000 miles on it. The car has been reliable for the eight years that I've owned it and I've had it serviced regularly because I use it to drive to work. Since I have to depend on it, I'm concerned about the fact that it starts fine when the engine is cold but it struggles to start when the engine is at normal operating temperatures. I've taken it to my mechanic but he can't find the problem. Everything checks out OK.
M.H. Tulsa, OK

A. Your Olds has its electric fuel pump submerged inside the gas tank and sometimes they develop a small internal leak that lowers the line pressure or the filter gets restricted. The reason that it starts easily when it's cold is because the cold-start system makes it rich enough to get it going but the system shuts off once the engine gets warmed up. Have your technician check the fuel pressure at the injectors and if it's low, he can go on from there.

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