Catalytic converter



I have a '99 Subaru Outback. The dealer quoted $1800 for a new cat. Should I go for a “cut and paste” non-OEM cat, or do I need to get the expensive option?

Part II: would I save the exhaust system by stuffing a rag up the tailpipe everytime I park the car, thus preventing moisture from condensing on the inside of the muffler/pipes/catalytic converter???

  1. You can go for a non-OEM, but I would make sure they guarantee it will not turn on the CEL. I’ve heard horror stories from some who put non-OEMs on that the CEL simply would never turn off. The cars ran fine, but wouldn’t pass emissions checks because of the CEL and/or the owners never knew if there was another code the computer was storing

  2. Absolutely NOT. In fact, you’d probably make things worse, especially if you forgot to remove the rag. As a 1999 model, your exhaust system should be made of stainless, even if it doesn’t look like it, and should last a LONG time. Moisture won’t kill it… and there will be condensation inside even if you plug it - the moisture is coming from the exhaust gasses, and it will condense in the pipes as the pipes cool. Plugging the pipes will only keep what moisture is there from draining.


Find a reputable independently owned and operated garage. Have him verify that the cat actually needs to be changed and if so use a direct fit aftermarket cat. You save hundreds, probably over a thousand.

This will not save the exhaust system and may even cause it to rot faster. As counterintuitive as it seems, your engine actually makes water and sends it down the exhaust. Gas is hydrogen and carbon atoms bonded, and when they seperate during combustion and the carbon bonds to the oxygen making CO2 and CO, the hydrogen bonds to oxygen and makes H2O. This water vapor has to dry out. If you stuff a rag in the end of the tailpipe you prevent any that’s entrapped in the system from doing so. You entrap moisture.

Keep the rag for wiping dead bugs off the headlights. let the exhaust system dry itself out.


NO; for every gallon of gas you burn you produce a gallon of WATER (H20). The secret is to blow this stuff out as fast as posible, and after the engine is shut off have as little as posible remain in the exhaust system.

The amount of moisture in the air is MINISCULE compared to all the water vapor created by burning gasoline. Your rag (which you would hopefully remove before starting the car) will have the exact opposite effect and would trap even more moisture in the system, and have the opposite effect of what you are trying to do. YOUR EXAUST HAS FAR MORE MOISTURE IN IT THAN THE AIR OUTSIDE, since all the oxygen combines to from CO2 and water.

When I was a kid, a favorite trick was to stuff a large Idaho potato in the tailpipe of a motorist we did not like. It would normally stall the engine.

With respect to the converter, I’m puzzled why you need one unless you failed to have an engine tuneup when you should have. A generic converter works just as well, but makes sure the shop you go to knows what they are doing. An independent shop specializing in exahust work would be ideal. That’s where I go. The dealer quote is high, as you say.

The real way to save money in car operation is to do all the required maintenance when needed, and NEVER postpone those items, like changing sparkplugs, beyond the mileage indcated. I have driven cat equipped cars since 1978 and have never had to change one.


Eraser and I were typing simultaneously.

I wanted to clarify the aftermarket cat converter apparent difference in opinion.

Many shops, Midas in particular (don’t go there), will weld in or jury-rig in a generic aftermarket cat not designed specifically for your vehicle. These can leave you with a CEL. The “direct fit” OEM-replacement converters I suggested are aftermarket converters designed specifically for your individual car, but not sold through the dealerships. They won’t say “Subaru” on them, but I’ve yet to see one cause a CEL light.


Thanks “eraser”, “the same mountainbike” and “Docnick” for your replies.

I will not stuff a rag up my exhaust pipe (or anywhere else) and I will go for the non-OEM cat.

I just purchased this car, so I claim no irresponsibility for non-timely maintenance.


Before you buy a “Cat”, replace the downstream oxygen sensor…It is this sensor that is throwing the “cat efficiency below threshold” code…


It may or may not be. The tech will have to look at the O2 sensor signal to find out.