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BACKYARD MECHANIC: Detecting source of whining can be difficult


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QUESTION: I have a 2004 Chrysler Intrepid and when it is cold outside there's an occasional high-pitch whine while driving. This can occur at any speed but generally above 80 km/h as I do a lot of highway driving. I'm not a mechanic but believe it has something to do with the throttle as I can make the whine go away by taking my foot off the accelerator or step on the peddle a little but it will eventually come back. I also had a 2002 Intrepid that had the same problem and the whine was a big factor in trading this car in on the 2004. I had taken both the 2002 and 2004 back to the dealership where I bought the car but they always said they had not heard about this problem before and could not duplicate it.

ANSWER: Locating a noise like this can be difficult. To pinpoint it better, more information is needed. For example, the noise could be coming from the electronic speedometer and only appears when it is cold. After the vehicle has been operating for a couple hours to warm up the interior completely, does the whine disappear? If so, check the speedo assembly.

Does the noise change if you change gears? The noise could come from rotating gears in the transmission and cold oil has a higher viscosity so the parts might not get the same amount of lubrication.

Computers, including the radio, on vehicles can make a high pitched whine that is only heard by some passengers. Electric capacitors or filters placed on the charging system can reduce some of the electrical noise in the vehicle electrical system and sometimes eliminate the whine, but on some vehicles even this doesn't work.

The whine could be coming from the power steering pump, where cold oil passes through the flow control valve. The whine could be the flow control valve vibrating rapidly.

As you can see, there are many sources of a whine. I doubt I have been able to help much but hopefully it will give you some information to start looking at operating conditions and symptoms when the whine occurs.

QUESTION: I have a question about engine oil. Can diesel oil be used in a gas engine? What problems can be expected?

ANSWER: There are many differences in oils designed for diesel engines compared to gasoline engines. One of these is the viscosity rating. Diesel oils often are a 10W-40 or 5W-40 rating while oils used in current gasoline engines use a lower viscosity 5W-30 or even a 0W-20 viscosity oil.

Another difference is in the API rating (American Petroleum Institute) for oil characteristics. The current API rating for 2010 and newer diesel engines is CJ-4 and CI-4 for 2004 engines. Gasoline engine oils currently use an API rating of SN for today's vehicles, The SM rating is for 2010 and older vehicles, SL rating is for 2004 and older vehicles and SJ is for 2001 and older vehicles. Some engine oils will carry a dual rating such as CJ-4 and SM, so they can be used in either gasoline or diesel engines if the viscosity is correct for the application.

Why have oils specific for diesel and gas engines? Diesel engines typically have higher loads and operate at lower rpm so they need less antifoam additives, they also must work with particulate filters. Gasoline engines operate over a wider rpm range, operate at higher cylinder temperatures and use fuels with ethanol in them. The oil is designed to be compatible with these operating conditions as well as having a lower viscosity to reduce internal friction and improve fuel economy.

Can you use diesel oil in a gas engine? Yes, but it may not be the best choice for your engine, Look for the viscosity and API ratings shown in the owner's manual or on the oil filler cap and use oils with those designations for the best engine operation.

Jim Kerr is an experienced mechanic, instructor of automotive technology, freelance journalist and member of the Automobile Journalists' Association of Canada.