Decades-old catalytic converter likely requires removal or replacement

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This article was published 20/11/2015 (3851 days ago), so information in it may no longer be current.

Question: My brother has a 1979 Pontiac Parisienne with 350,000 kilometres. It has a 350 cubic-inch V-8 engine. It has the original catalytic converter. He was told by a mechanic and others that with such high mileage the converter cannot be functioning properly. Is there a way to test this? Would poor gas mileage be a symptom? He was told if he removes the convertor and replaces it with a straight pipe the car would not run properly. Is this true and how would it affect the performance? Your opinion would be greatly appreciated. Klaus

Answer: With mileage that high it is unlikely the catalytic converter is still working properly. During normal use, the catalytic converter only causes a chemical reaction in the exhaust gases to convert them to less-harmful gases and does not consume itself, but with that mileage, it has likely become contaminated so the exhaust gases can’t come in contact with the catalyst.

It is possible to test a catalytic converter. The best way on older vehicles such as this one, is to use an exhaust gas analyzer to see if harmful gases are being converted. Most shops don’t have exhaust gas analyzers, but they were used to tune many of the European cars in the 1970s and 1980s, so you may find one of these repair shops will be able to test it. Since 1996, vehicles have had an oxygen sensor behind the converter so the engine computer can test the converter as part of its diagnostic program.

Poor gas mileage would be a symptom if the catalytic converter is plugged so exhaust gases can’t flow through it. Many of these vehicles had the converters replaced with a straight piece of exhaust pipe and they run fine, but exhaust emissions will be higher. Because there is no monitoring of the converter by the engine computers before 1996, there will be no change in engine operation.

 

Question: Yesterday, the temperature light on my Chrysler Pacifica came on, so I cut the engine off and checked if it needed water. It was a little low. Then I’m driving home and my vehicle kind of jerked forward a bit and eventually died on me. It was smoking a little bit (the coolant was full) so I let it cool down and tried cranking it and it turns over but doesn’t catch. My mechanic sent me a video today of what it’s doing. There is a lot of smoke coming out of the oil filler cap opening when the cap is off and if you pull the dipstick out there is a lot of smoke out the tube too. He thinks I need a new motor. I just need a second opinion. Layne

Answer: I would have to agree with your mechanic. The large amount of smoke coming from the oil filler and dipstick indicate too much crankcase pressure and the only way for that to happen is if combustion gases are allowed to enter the crankcase. The most likely path for this to happen is past the piston rings and with the large amount of “blowby”, as it is usually referred to, I would suspect either several of the rings are broken or one of the pistons has a hole in it.

This could be unrelated to the temperature light coming on, but if the engine has been overheating, the cylinder heads can warp and the head gaskets no longer seal properly. This can allow coolant into the combustion chamber, which would cause white smoke out of the tailpipe, especially when starting the engine. The coolant can also leak internally into the engine oil and will damage the engine bearings.

It appears you have serious internal engine problems and the cost of repairing your existing engine is likely much more than replacing it with a good used one or a factory rebuilt engine.

 

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