While washing RX-8 today I noticed a heavy buildup of soot on the lower surface of the inside of the pipe. Its on the bottom as if a liquid had flowed out, but I have never seen any spots or stains under the car.

Is this a normal occurance for rotary engines, part of the oil injection into the system. I'm not concerned yet just curious.

Thanks for the help.

 

I think Mr.jtdwab has hit the nail on the head, she sure do run 'pig-rich'!

The black is a sure sign of rich mixture, as any old time mechanic will tell you. It is strange that it collects at the bottom of the pipe like it does, probably coming out with the start-up condensation...

To burn enough oil to show the same symptom, you would see clouds of blue smoke behind your car. I have cleaned the black off three times in the last 800 miles, and my oil level is still where it started - 2/3 up the range.

Averaging 20/21 mpg over the last 500 miles, it SEEMS to be getting better mileage now......
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doc

 

I have heard theories in the Fuel Economy threads that the 8 may be intentionally programmed to run rich during breakin for some reason. That would also explain the poor mileage at first. We'll see if both phenomena clear up.

Next question: What's the best way to clean these deposits? I've got the same thing as jtdwab.

 

I try to wipe my tailpipe with a rag each time I take her out. Same result, it just gets all black and sooty again. Last week, drove over to our dealer, showed the service manager, he said didn't look right to him and he would attempt to find out what was happening.

Nothing back yet, but I noticed this since the first day or so. Strange and out-of-the-ordinary.

 

Heh, welcome to the world of rotaries. It is NOT out of the ordinary.

 

Yeah, that's normal and fine. Use some chrome polish on the tips when you wash the car and they'll sparkle like new.

Dale