Motoring Q&A: Aftermarket parts OK for aging Lexus?

Q: I've been told that the catalytic converter on my 2007 Lexus 350 with 100,000 miles on it has failed. I intend to keep my "retirement" vehicle for a long time. Can I have a shop install an aftermarket converter to save a lot of money? Will it be as satisfactory as a factory-new converter? Also, my 2007 Chevy Impala SS with 60,000 miles uses two quarts of oil per 1,900 miles. I've been told that an engine flush with each oil change could help. With this level of consumption, what type and weight oil should I use?

A: Your Lexus has a pair of catalytic converters, one incorporated into each of the two exhaust manifolds on the V-6. The cost of original manufacturer Lexus manifold/converter is roughly $750-$1,100 each plus installation, depending on whether your Lexus is an ES350 or GS350. You're right! That's a lot of money to spend on a nearly 10-year-old vehicle.

Yes, you can take the car to your favorite shop to have aftermarket manifold/converters installed. Part prices online range from about $200-$400 each and they appear to be direct replacement units.

In regards to your Impala SS, I found an interesting service bulletin addressing excessive oil consumption on this 5.3-liter V-8 engine. The bulletin addresses the possibility of carbon buildup causing the piston rings to stick, thus allowing excess oil into the combustion chambers.

This engine is equipped with GM's active fuel management, or AFM system, formerly called disable on demand, or DOD. This system utilizes engine oil pressure to disable specific valve lifters to turn off four of the engine's eight cylinders during light load operation such as cruising on the highway. The system effectively traps the exhaust gases in each of these cylinders during AFM activation. After the exhaust gases are compressed on the compression stroke, they act like a spring to help push the piston downward on what would be the power stroke in normal operation. This spring-like action helps reduce pumping losses in the disabled cylinders.


Apparently, during AFM activation, excess oil from the AFM pressure relief valve may collect on cylinder walls and eventually carbon-foul piston rings. The fix, as per the bulletin, is to de-carbonize the cylinders with GM Top Engine Cleaner or SeaFoam, then install a redesigned oil pan gasket that incorporates a new AFM shield to keep the excess oil spray off the cylinder walls.

Q: My 1999 Saab 9-5 with 107,000 miles died at an intersection recently. I was able to start it and traveled another few blocks, but the car died again. This time I was unable to restart the engine; the battery had died. The Saab was towed to my mechanic, who jump-started the car. My mechanic narrowed the problem down to either a fuel pump failure or a crankshaft sensor malfunction. But since the car started after the jump, the mechanic couldn't really pinpoint the problem.

A: Since the car restarted properly after being towed, make sure the battery and alternator are good. Cars don't run well without electrons.

I'm more inclined toward a problem with the fuel pump, fuel pressure or exhaust back pressure. Your mechanic could check the electrical current that the fuel pump is drawing. Typically, fuel pumps draw roughly one ampere of current for every 10 psi of pressure. Your Saab needs 43 psi of fuel pressure, so the current draw should be in the range of 4-5 amperes.

Also, with the age of the vehicle it might be possible for debris and/or contamination in the fuel tank to slowly clog the fuel strainer and restrict fuel flow from the pump to the engine. After the engine dies, the debris falls back into the tank so the engine restarts and runs for a while until the same thing happens again. Another possibility is a restricted exhaust system or plugged catalytic converter. The restricted exhaust chokes the engine until it dies, then back pressure dissipates and the engine starts again.

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