Q. I bought a new Infiniti QX4 in 2002. Since the beginning, I have been diligent about regular maintenance. The truck has 112,000 miles. The past few years I have been dealing with repairs such as brakes, front and back calipers, exhaust system, and on and on it goes . . . I am now facing another hefty bill. I have a coolant leak that concerns the rear coolant bypass. I was told by the dealership the coolant bypass is located behind the engine up against the firewall. I was advised that they recently replaced this hose on another QX4 and the only way to access this part was to drop the engine. Twelve hours and $1,800 later they fixed it. I am trying to avoid this situation and have called Infiniti’s consumer affairs office. The person I spoke to in that office said they could not help me, as they stand by the dealer. I have not yet placed a call to the general manager of the dealership, but that is next. I suspect that conversation will end badly! Do you know if this repair can be done another way? It would seem to be a design flaw if that is the only way to repair the rear coolant bypass.

A. The cooling bypass tube is in a very difficult place to repair. Over the years I have seen the design of many vehicles become complex and labor-intensive, for what should be simple repairs. My favorite example is when I was working as a technician on a Toyota van that required the engine to be removed for a basic tune up. Talking to various Infiniti and Nissan dealers, it takes seven to eight hours to perform this repair. It is my understanding that the transmission needs to be removed. Additional research on some technical Web sites suggests the repair can be done in as little as two or three hours by removing the engine support, radiator shroud, and lowering the engine for access. Perhaps an independent shop may provide a more reasonable repair.

AC blowing warm air

Q. I have a 2004 Mercury Grand Marquis. In 2006, the air conditioner was doing nothing but blowing warm air. I took the car to the dealer on several occasions for this problem and the air conditioning worked for about a year. Last year I went without air conditioning again; what do you think is wrong? I assume there is some sort of leak. The car is under an extended warranty.

A. I would go back to the dealer and have them check the system for a leak. If they determine the system is low on refrigerant, they will use an electronic tester to find and repair the leak. If the system is fully charged, the problem could be electrical. In using the appropriate scan tool, a technician will check for trouble codes. There could be a problem with a switch or relay that prevents the system from operating properly.

PCV may be clogged

Q. I am writing in regard to Ted’s question (from East Providence) about an oil-burning smell in his Audi 2.8L. I have the same 2.8L engine in a 2001 Passat that for the last year or so has an intermittent, but sometimes overwhelming, burnt oil smell coming in through the ventilation system. It is most prevalent when braking to a stop. I would look, but see no obvious leak within the exhaust manifold, which is what I suspected. I recently traveled a few miles to a local store, when getting out of the car discovered a huge puddle of oil on the ground under the engine. Expecting catastrophic engine failure we did not get the new mattress we needed!

The engine was literally covered in oil; however, the car restarted and ran fine. The reservoir was only down about a quart, so we drove it to our trusted mechanic. He de-greased the engine and put dye in the oil, but nothing happened again — absolutely no further leaking! We still have had an occasional burnt smell, but not the “leak.” Could there be some kind of release or blow-by valve releasing oil intermittently? We suspected the external oil filter return line was damaged, but it seems fine. Any theory or ideas would be appreciated. I hate to bring it in to the VW dealer and have them guessing at $75 per hour!

A. The problem could be a clog in the PCV system. The engine in your car uses some plastic tubes and a part Volkswagen calls a “suction jet” that allows the PCV system to work properly. If the tubes are clogged or the suction jet is faulty, excessive pressure will build up in the crankcase and an intermittent leak is certainly possible.

Belt needs to be changed

Q. I have a couple of concerns regarding my 1994 Ford Taurus with 87,500 miles, which is regularly serviced. At 100,000 miles the maintenance schedule calls for the replacement of the “camshaft drive belt.”Is this the same as the serpentine belt? (The serpentine belt was recently replaced). If it’s not the same, could you give me some idea as to its purpose and the total cost to replace this camshaft drive belt? Also, what would be a reasonable amount I should expect to pay to replace the car’s muffler system, should it be necessary in the near future?

A. There were three engines available in 1994 for the Ford Taurus; a 3.0 liter, 3.8 liter and the double overhead cam 3.0 liter in the SHO Taurus. The high performance SHO engine is the only one with a camshaft drive belt. The other engines use timing chains, which generally don’t require maintenance. Regarding the cost of an exhaust system, the prices can vary from shop to shop. In most cases, the exhaust system from the catalytic converter back will need replacement. Expect to pay two to three hours labor plus the cost of the parts. The muffler can cost as much as $400 for a factory system to as little as $25.00 for a universal muffler bought from Web sites such as rockauto.com.

Some Camrys vibrate

Q. I have a 1995 4-cylinder Toyota Camry 4 door with 130,000 miles. When the weather is cold, there is a vibration that comes up through the steering wheel when the car is stopped and my foot’s on the brake, such as at a stop sign or stop light. There is no vibration when the car is moving or when the car has been warmed up; even after the car is stopped in drive there is no vibration when the engine is warm. (The length of the “warm-up time” seems to depend on how cold it is outside. In the last year to 18 months the timing belt was changed at 120,000 miles, it had a major tune-up and had the transmission flushed. Within the last four months all four of the motor mounts have been replaced as well as new spark plug wires and spark plugs. The last mechanic also checked the timing belt to see if everything was in-sync and firing when it was supposed to. All things are fine in that respect and the car performs and shifts fine. The mechanic’s gut feeling is that the converter in the transmission may be out of whack, but he is not sure. Again, when the car is warmed up or it is a warmer day the vibration is not there, or one may think that a slight vibration is normal?

A. The four cylinder engine in the Camry has been problematic with some engine vibration. As the car gets older, the vibration can get a bit worse. Your repair shop seems to be looking at all the right things, although I would look at two more areas. The valve adjustment is frequently overlooked. To be evaluated correctly, this adjustment should be performed on a cold engine. The other possible problem area is dirt and carbon built up in the throttle body and idle air control motor. Although both possibilities seem relatively simple, they can cause a vibration.

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