Hi all,

In my first thread on this forum i posted that i was going to do a little experiment to see if the sooty exhaust issue on the new DFI engines is somehow related to the use of 7th gear+low rpms.

Well, i did 2 tests:

1- First i cleaned the tips thoroughly(they turned back to grey) Then i added a full quart of oil to the engine(Mobil-1 0w-40). For the next 2000Km, i drove the car like i usually do (Hard) but ALWAYS stayed in manual mode to avoid shifting into 7th. I also changed gears at 4K rpm(depending on the situation). After i completed the 2K mark, i inspected the tips and they were dirty(black-ish). however, they were NOT sooty or had built up gunk that was dripping from them. Also after that i needed to add half a quart to top off.

2-Did the same thing over again, cleaned the tips made sure the oil level was full etc. This time i left it in auto mode for 90% of the time and used 7th gear. And now, 1700Km later...the inside of the tips is charcoal black. The tips in the first test would be considered clean if compared to their state after the second test. But what really confused was that the car somehow burned almost a whole quart in 1700Km VS half a quart in 2000Km. That puzzled me since i was under the impression that hard driving= more oil consumption but it seems the other way around....at least in my case.

I would also like to note that i am very careful when adding oil and i take multiple measurements to insure accuracy( leveled ground, turn off the car for 5 minutes and check again etc.)

I will make SURE to mention this after i take my car to be serviced at the dealership on the 16th.

Anyone care to chime in on this annoying issue? It obviously looks like the fuel air mixture is too rich(I am no mechanic )....but why ? when should this oil consumption stop?
Honestly, i will really consider software(softronic-giac-evomsit) JUST for the air fuel mixtures if the dealership decides that " thats normal and all of the cars do it"

 

These suckers drink oil. I have a white 6MT '09S and after washing the car, not only do I notice black particles on the rear bumper, but there is also some oily residue on it as well. I'm a chemist by training so I analyzed the black particles with a Fourier transform infrared spectrometer and yup, it's soot.

With 9K miles on my car, I'm getting about 2000 miles /qt oil.

If you mention it to your service mgr betchya he tells you it normal

 

While I have not noticed the soot accumulation on my wife's 997 C4 PDK I will pay more attention. I enjoy the car enormously, the PDK is exceptional but I don't drive it that often. Ironically when I do, it is in manual mode and I typically do not use 7th gear; it feels like I am bogging down the car in normal driving conditions. I use 6th for most highway driving so I can keep the revs >3000 rpm while cruising. The car is much more responsive and fun. I have to be cruising at 85+ mph to use 7th at all. The 3.6L engine in the C4 does not like spinning at <3000 rpm unless it is parked. I can't imagine the 3.8L in the CS is any different w/ respect to low revs. Just some observations that may lend anecdotal credence to your experience with soot accumulation.

 

I agree the car is phenomenal! but its these little issues that ruin the whole experience if you know what i mean. PDK is also amazing. However, if you drive the car in normal auto, it doesn't feel like a sports car at all.

I went back to my normal driving(manual- hard, rpms above 3K) . I will see whats the result of going back to that method.

 

Hi,
Any updates?

Many Thanks.

 

I also have found that keeping the RPM up above 2500rpm cut down on soot.

When I do a track day my car does not see anything below 4k rpm unles I am driving in the pits. At the track I have zero soot and my exhaust tips have a clean to grayish white look.

 

Maybe this is a simplistic explanation, but higher revs typically equal higher speeds which in turn equals higher exhaust velocity away from the tips. The harder you drive, less exhaust 'soot' is getting caught on the tips because you are literally out-pacing the exhaust gas.

The converse: the lower the rpms, the lower the speed, meaning the trailing exhaust is more likely to get caught in the 'wake' and therefore get caught on the tips.

I like the idea of driving harder to keep my car cleaner

 

That explanation could be it .

Just to post an update, I changed the cars oil from mobil-1 to castrol edge and the car has experienced ZERO oil consumption in 4000Km. Is it the engine breaking in(20K)? or is it the oil? im not sure...
Give it a try , u have nothing to lose.

 

What weight of Castrol Edge did you use?

 

Its the castrol edge sport 10w-60

not on the approved list by porsche btw. The castrol edge is 5w-40(or 0w not sure) and is approved by porsche.

 

Proper exhaust color should be grayish white. For some reason the dfi cars... My Carrera S and Cayanne S both run rich at low toms and burn better at higher rpm. The soot you see on the exhaust tips is not oil