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THE CAR DOCTOR

Finding the leak in cylinder-head gaskets

Plus: Misfiring, waiting for a third Saab transmission

By John Paul, AAA Car Doctor
October 16, 2008

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Q. After the 15,000 mile service on my 1999 Lexus, the mechanic initially thought I had a leak from the water pump. I brought the car back for him to inspect it and then he stated the problem was more likely the cylinder head-gasket. He only performed a visual inspection and pointed out a small area under the vehicle that had whitish residue. Is there a better way to determine if this is a real problem other than a visual inspection?

A. Cylinder-head gaskets can leak both internally and externally. If the leak is internal, the coolant will be burned as the engine is running. If this is the case additional testing can be performed. If the leak is external, a visual inspection is usually the best method. To truly verify the leak, some mechanics will add a dye to the coolant and using an ultraviolet light can more easily spot the source of the leak.

Q. I have a 5-speed Mercury Cougar. When going from a stand still while facing up hill my car hesitates when I hit the gas and there is a popping noise under the hood. Any ideas?

A. The car sounds as if it is misfiring under load. This could be due to worn spark plugs, faulty ignition wires, or even a serious engine problem. At this point you need to bring the car into a repair shop and have the engine analyzed.

Q. In your opinion, what is the best medium-size pick for pickup trucks on the market today?

A. At one time there were compact trucks and full-sized trucks. Now most compact trucks have grown to mid-sized proportions. If you are looking for a true mid-sized truck, the Dodge Dakota is the best choice. If something smaller will do, it's hard to find anything wrong with the Toyota Tacoma.

Q. My 2003 Saab 9-5 is on its third transmission (number two and three are under warranty). My Saab dealer has been trying to install transmission number three for over five weeks now with no luck. They did provide a loaner but it has been over a month. What can I do?

A. I'm not sure why it would take five weeks to install a transmission. At this point it sounds as if the dealership needs a little help. I would ask if a Saab field technical engineer could be brought in to help get your car back on the road.

Q. My wife has a 1995 Mercedes E320 with an odd problem. The car starts fine in the morning but after it has been driven, shut off, and restarted (after idling for about 30 seconds), the engine takes a 500 r.p.m. drop and stalls. The really odd part in this is that it doesn't matter if it is summer or winter or whether the car has been driven for five minutes or five hours. The only way around the problem is to restart it and hold the idle up about 1,500 to 2,000 r.p.m. until you get the drop, which, at that engine speed, is just a "blip". Once you get past the "blip" the car idles fine at the proper r.p.m. and there is no further problem until it shut down and restarted. The car has passed at least one state emission inspection in this condition. There are times when I yearn for the days of carburetors and having a 1/2" and 9/16" wrench was all you needed to fix a car. Do you have any suggestions?

A. The most common problem with this model is a faulty mass air flow sensor. These sensors fail due to contamination from dirt and other road debris. The dirt particles make their way to the sensor in most cases because the air filter was installed incorrectly.

John Paul is the public affairs manager for AAA Southern New England. He can be reached at jpaul@aaasne.com.