I keep reading posts regarding cats. They seem to be a common source of problems. I understand that misfire s will destroy them. Are there other reasons they can go bad? If a car is we!l maintained, how long will a cat usually last?

 

The cat is usually only a problem if you ignition health is questionable. If you keep on top of that, it can last a very long time (at least 200,000 miles).

 

What kills cats is :

- a lot of unburnt fuel, oil or other carbohydrates in the exhaust flow. Misfire or incomplete combustion from weak ignition creates those conditions, so does burning a lot of engine oil. They heat up and clogged with caked on carbon deposits

-heavy metals present in some oils. Zinc for example. It chemically neutralizes the catalyst.

-physical damage (impact or exhaust pressure). The stock cat is set of ceramic plates. They can crack and crumble. If they clog, the pressure on them increases causing them to crack and crumble.

It could last the lifetime of the car. A cheap generic replacement on an RX8 could last 2 weeks. They're not made the same.

 

Loki,
What is considered a lot when burning engine oil?

 

Idk what Loki thinks, but depending on your driving habits, I think anything over half a quart every 3rd or 4th fillup is excessive if you drive normally.
If you drive it like you stole it, adding a little more often is normal.

There is some useful info in this thread, plus the entertainment factor of the now banned monchie's idiocy.

https://www.rx8club.com/series-i-tro...-212932/page2/

 

In racing I burn about 0.75L of oil per tank. In normal driving, like BC says half a quart every 3-4 tanks sounds right.

 

Mazda says that one quart every 500 miles is acceptable for oil consumption.

As far as catalyst life, I can tell you that my Brilliant Black 04's converter was replaced once under warranty. This was before I bought the car and when the car was in the 3/36 period. Original engine failed at 94k miles and I replaced the engine and I am still using that second converter. My Nordic Green 04's converter was replaced shortly before its original engine was replaced at 75k miles and the car now has 134k miles and a dead engine. I pulled the converter and it looked fine so I reinstalled it.

Converter failure depends on quite a bit as Loki mentioned. Misfires will quickly destroy a converter and unburnt fuel detonating in the converter or shortly before the converter will surely do it. This is whey we must maintain our cars properly. Plugs, wires, and coils are something to stay on top of. I pull my plugs twice per year. In the spring I check their condition and check for wear, rust, and carbon buildup. And I do the same about a month or so before I store the car for winter. I visually inspect the wires and coils at the same time. Since I have a BHR setup on my BB 04, I don't mess with the coils so much. That coil setup is fantastic.

 

Thanks guys for all the info. I'm learning a lot.

 

My mostly stock S2 burns right at 0.5 qt per 2 track hours, which equates to ~1.5 tanks. It burns a lot less on the street--probably 0.5 qt per 5 tanks.

 

I have the MazdaManiac tune with increased injection rates. But yeah it sounds about right. It's a full bottle of Lucas semi-synth per track day, 4x25m sessions (+ driving there and back), 1.5 tanks-ish.

 

Yeah, I premix 1oz per gallon for track duty as well. 1/2oz per gallon for street duty.

 

From the UK forum.............How do cats die......

Relevance of highlights:
- Rotary engines have among the highest exhaust temperatures of any road vehicle.
- Cheap aftermarket cats often use a higher proportion of rhodium than the other (more expensive) options.
- Excess oil in the exhaust is a cat killer; whether that's from frequent oil burbs, worn seals, or over-enthusiastic premixing.
- The Renesis Secondary Air System actually uses the process of in-cat fuel burning, for a very short period following a cold start. A problem with (or the removal of) the air pump, can damage the cat as this excess fuel can't get burnt off before the cat reaches the critical temperature.
- A (partially) blocked cat will stop the engine revving properly, before it then goes on to cause internal engine damage, and/or sets the car on fire.
- Bad ignition components are common on the RX8; HT leads rot at the ends, coils fail, plugs don't get changed as often as they should.
- O2 sensor problems aren't unknown on the RX8 but dirty MAF sensors or badly designed aftermarket intakes (or just damaged air meshes) can also cause incorrect inputs to the PCM and result in fuel over-rich or under-lean. Any pre-cat leak in the exhaust system can also cause the mixture of gases through the cat to become critical.
- Many cheap aftermarket cats have a weak internal structure and simply fall apart under the strain of the rotary exhaust.
- Vibration can also be a cat kill, especially of the joint at the rear of the cat is incorrectly fitted, such that it can't move as it should.
- Thermal shock can also damage the cat, e.g. driving the car with a hot cat into deep water/snow.

https://www.rx8ownersclub.co.uk/foru...65957#p1165957