Dayton Daily News

My 1986 Nissan pickup bucks when the tachometer reaches 3000 rpm. This even happens in fifth gear. Do you have any idea what causes this? D.T., Lexington , Minn.

A: Ride’em, cowboy! The engine is misfiring. This could be caused by fouled spark plugs, failed spark plug wires, cracked distributor cap, failing ignition coil, failing ignition module or a faulty distributor rotor. It’s also possible there is excessive wear in the valve system, worn valve springs, worn valve guides or an excessively worn cam shaft. Also, a fuel filter that is restricted with sediment could cause symptoms such as you describe.

If the spark plugs, ignition wires, distributor gap, rotor and fuel filter haven’t been replaced in a while, consider that it’s time to replace these parts. Hopefully this will cure the condition so you don’t have to spend big bucks on valve system repairs.

Carbon monoxide poisoning

Q: My idiot friend left my 2002 Chevrolet Cavalier with 55,000 miles idling in my garage overnight! It ran for approximately 12 hours before I found it running. I’m not a brain surgeon for letting him use the car. I also should have checked to see if he turned it off. He says it’s not a big deal. Did he cause any damage? Is there anything I should do? K.B., e-mail

A: You are lucky you weren’t overcome by carbon monoxide fume poisoning. People have accidentally died as a result of forgetfulness. This has happened when vehicles are left running in a garage that is attached to a residence.
Also, it doesn’t matter if the garage overhead door is open. Exhaust fumes can still concentrate in the residence and kill.

As for the car, there is a danger that it overheated. Make sure it is running as designed. If not, have a technician check it over.

Also, it would be wise to change the engine oil and filter as the oil may have suffered heat-related wear that could impair its ability to properly lubricate the engine.

It’s also possible the transmission fluid overheated. The fluid may need a flush. Also, the catalytic converter might need replacement.

As for what you should do now, don’t give the keys to your friend until he can demonstrate the ability to turn off the ignition.

Engine burns excessive oil

Q: Last August I purchased a 2004 Buick LeSabre from a Buick dealer. It had 7,081 miles on it at the time of purchase. I changed the oil and 1,200 miles later the check oil light illuminated. It was a quart low so I added oil.

I returned to the dealer where the oil was changed. They also started an oil consumption test. In 3,045 miles, the engine used
3.75 quarts of oil. I’ve owned cars since 1953. I have never had a car use this much oil.

Dealer personnel are checking with General Motors about the oil usage, but they seem to be putting me off. Do you think the oil usage is normal for this car? P.D.W., Woodbury , Minn.

A: According to a General Motors technical service bulletin, the acceptable oil consumption is 1 quart in 2,000 miles under normal driving conditions. If you carry heavy loads, tow a trailer or hot rod the car, the engine will use more oil.

If dealer personnel don’t get back to you quickly about what they are going to do about the condition, consider contacting General Motors to file your concerns about the oil consumption.

Repair could be as simple as curing a restriction in the crankcase ventilation system or as extensive as replacing the engine.

What needs to be done to cure the trouble will likely be determined by a dealer technician once the factory gives authorization for repairs.

Check engine light not sign of big trouble

My friend has a 2000 Jeep Cherokee. Several times the check engine light has turned on and remained on for several days, but for some reason it mysteriously turns off. Whether the light is on or off the vehicle runs fine.

Is this a critical situation? Will the computer reveal a trouble code for the problem? T.D., e-mail

A: Since you say the vehicle runs normally illumination of the light probably is not the result of some critical problem. This could be the result of a lazy oxygen sensor, failure to shut off the engine when fueling the vehicle or even perhaps the result of a dirty air filter.

To find the cause with certainty there is a better chance to detect a fault when the light is on. However, the computer does have a memory that records and holds diagnostic trouble codes for a prolonged period depending on the number of ignition key cycles and miles driven. Since this is the case if the light should turn off just before a scheduled shop appointment computer diagnostic codes more than likely will be held in memory for a technician to access.

When a technician retrieves the codes a diagnosis and lasting repair should follow.

Lowered Tailgate Posses Safety Hazard

Q: As a military pilot and aerospace engineer I read with interest your answer to a question about fuel economy on a pickup truck with the tailgate up or down. I have read similar answers from other auto columnists.

My concern is with the tailgate down it posses a safety hazard. If a vehicle hits the truck from the rear or the pickup is backing up the tailgate extends beyond the bumper and can cause damage to other vehicles. Not only this, but if there is cargo in the bed it might slide out.

Also water collects in the tailgate. This can cause corrosion to the metal.

Can you comment? L.T., e-mail

A: Many readers commented on my answer. Some mentioned a television program that analyzes myths. Readers who based their comments on a television show stated that fuel economy goes down when the tailgate is down. My answer was that I had not read any laboratory studies on whether fuel economy goes up or down with the position of the tailgate.

As a former military aviator I too am familiar with aerodynamics but you raise important safety concerns that pickup truck operators might consider. The tailgate can pose a safety hazard. If you are considering lowering the gate to experiment with fuel economy you might also place a red flag on the gate or other devices to help make it more visible to you and other drivers.

Also, you might consider removing the gate all together as sometimes when the gate is down and you hit a bump the gate bounces. This can damage the sheet metal and trim. I’ve seen some so damaged they no longer latch to close. Also, if you lower or remove the gate be sure to secure any cargo so it doesn’t slide or blow out of the box and hit trailing vehicles or pose a road hazard.

Today’s Oil Better Than Long Ago

Q:Many years ago about the time multi-viscosity oil was first introduced I took an auto mechanics class in night school. As part of the class I learned about multi-viscosity oil. The instructor said that oil such as 10W-30 suffers molecular breakdown during extended use.

Is this true? What is extended use? P.K., Huntington Beach, Calif.

A: Multi-viscosity oil has been around a long, long, time. Back when it was first introduced the recommended oil change interval on most cars was every 1,000 miles. Motorists who lived in suburban areas and motored to work in urban central business districts such as New York, Los Angeles and Chicago were changing the oil and filter every month. This was because the additives in the oil that make it change viscosity breaks down.

The additive package in today’s multi-viscosity is better than it was 40 years ago. Also, engines are much better. As a result, oil and filter change intervals have increased from 1,000 miles to 3,000 miles on vehicles driven in city traffic or suburban short trip travel.