Q: I purchased a new 2013 Buick LaCrosse with the six-cylinder engine in January 2013. It currently has only 10,300 miles on it. During cold mornings prior to the vehicle coming up to full operating temperature there is a squealing noise when accelerating from a stop. Once the engine is warmed up the noise seems to go away. It sounds very similar to a fan belt slipping. The dealer inspected the fan belt, idler pulley and engine pulleys, finding nothing wrong. They reported they were unable to hear the noise, likely because the engine was up to temperature when they inspected the vehicle. Can you help?

A: Typically, a squealing noise from under the hood when the engine is under load is caused by slippage of the fan/serpentine drive belt. This crankshaft-driven belt drives the water pump, alternator, air conditioner compressor and power steering pump.

In this case, the belt slippage/squealing when cold may be caused by excessive drag from the power steering pump. My ALLDATA automotive database pulled up TSB #12-02-32-002A dated June 2013 that suggests inspecting power steering components for high-pressure damage and replacing the power steering fluid with GM's "cold climate" power steering fluid.

Q: Referring to the second question in your Dec. 6 column: You didn't say anything about why the dealer recommended only their oil. Wouldn't store-bought oil be good enough?

A: I didn't respond specifically to this question because the answer seemed obvious — neither the dealer nor the carmaker manufacture "their" motor oil. Many carmakers choose to offer motor oil blended by an oil company to their specifications. But the key point to remember is the American Petroleum Institute's "Engine Oil Licensing and Certification System" — EOLCS — that is accepted by oil companies, car and engine manufacturers worldwide. If the oil meets these standards, it can carry the API Service Symbol "Doughnut" and Certification Mark "Starburst."

The API "doughnut" identifies the lubricant's performance level, viscosity and energy conservation properties. Current performance standards are "S" (service/gasoline — currently SN) and "C" (commercial/diesel — currently CJ-4). Viscosity, 5W-30 for example, refers to the oil's flow characteristics based on Society of Automotive Engineers ratings. "5W" represents the oil's flow characteristics on a winter cold start. The "30" indicates its flow characteristics at full operating temperature.

The "Starburst" symbol means the oil meets the most current requirements established by the International Lubricant Standardization and Approval Committee — ILSAC. The current ILSAC standard is GF-5 for passenger cars.

So what do all these symbols, letters and numbers mean for car owners? Simply this: If the labeling on the motor oil meets or exceeds the carmaker's requirements as shown in the vehicle's owners manual, the lubricant is acceptable for use in that vehicle — no matter who makes, markets or sells the oil.

Q: I have a 2010 Toyota Venza with 50,000 miles. Starting at about 60 mph, there's a medium-tone hum from the rear of the car that oscillates off/on about every second. The tone doesn't change on acceleration, deceleration or in neutral. At 60-70 mph, turning left makes the hum a little louder and oscillations faster, while turning right makes the oscillations slower and hum dissipate. A new set of tires were recently installed with no change to the symptoms.

A: Your self-diagnostics eliminates tires and points toward differential, driveshaft, CV joint or wheel bearings. The characteristic of hum and oscillation frequency increasing when turning in one direction makes me suspicious of CV joints and differentials (you didn't mention whether your vehicle is FWD or AWD). If it's front-wheel drive, the rear hubs and wheel bearings are suspect. If it's all-wheel drive, add the rear differential and carrier bearings to the list.

When turning, the spider gears in the differential allow the outboard wheel to rotate faster than the inboard wheel, accelerating the outboard drive axle, carrier bearing and wheel bearing and decelerating the inboard components. This might explain the change in hum characteristics.

———

ABOUT THE WRITER

Paul Brand, author of "How to Repair Your Car," is an automotive troubleshooter, driving instructor and former race-car driver. Readers may write to him at: Star Tribune, 425 Portland Ave. S., Minneapolis, Minn., 55488 or via email at paulbrand@startribune.com. Please explain the problem in detail and include a daytime phone number. Because of the volume of mail, we cannot provide personal replies.

———

©2014 Star Tribune (Minneapolis)

Visit Star Tribune (Minneapolis) at www.startribune.com

Distributed by Tribune Content Agency, LLC