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Hi All,
I have a theory I want to test out here in hopes it may help a well known issue on the 996TT smokey start ups.
History: My 996TT has 64K on it and every so often it would smoke on start up. Consistently if it was a short run cycle (moving out to wash then put back into garage) but occasionally it was also after an extended drive. Could never pin down a solid reason.
Last oil change was in the fall last year before winter storage. While the oil is draining out I was cleaning out the filter housing and noticed the bypass spring in the center post. It was pretty gummed up with sludge as it was probably the first time this was ever done. Used a toothbrush and some valve cleaner to remove every last bit including the area accessible when compressing the spring. Drove it about 20mi away to put in storage until mid April this year.
As of today and about 1 month of driving, it has only emitted smoke once and that was after 3 or 4 short run cycles. Other than that no random, James Bond worthy smoke screens have occurred.
Theory: The bypass valve gets clogged and gummed up over time and allows for oil to leak by on occasion. Cleaning this allows it to seal properly and prevents this condition from happening.
If anyone out there has a chance to try this next oil change or just wants to check theirs it would be very interesting to know if it has a similar effect. Photo attached for reference
Typically its a blue-ish white color and smells like oil. I try to make it a point to idle for 10-15secs prior to shut down but that didnt seem to have a direct effect from what I observed
Typically its a blue-ish white color and smells like oil. I try to make it a point to idle for 10-15secs prior to shut down but that didnt seem to have a direct effect from what I observed
you should idle down for 3-5 mins... blue smoke probably means oil is getting past the oil seals in the turbo... this is same for me...
you should idle down for 3-5 mins... blue smoke probably means oil is getting past the oil seals in the turbo... this is same for me...
try 3 mins next time...
I dont disagree that this could help, but its not always feasible to sit and let it idle for that much time, like say if your just running to a store or an associates house. My observation is that from cleaning out this bypass valve, the instances for my car at least have not re-appeared. Plus from a maintenance stand point, cleaning out sludge build up is always good to do less it dislodge and go somewhere it shouldnt.
Use whatever approach you prefer, I am just stating a hypothesis
That is difficult to believe because the catalytic converters have zero affect on the oil and oiling system of the car.
Are you doing what Kamlung suggested, letting the car idle for a few seconds before shutting it down? Or were the turbos serviced when the exhaust system was changed? Because that is more most likely the cure.
Only driving hard. The turbos will cook the oil in them if they are red hot. It won't happen if you've been cruising. The issues here are probably from worn turbo seals or leaky check valve in the turbo oil inlet. I installed some turbos that didn't have the check valve because I didn't know at first and they smoked on startup.
Leaky turbo seals may be a factor in the occasional smoke at startup but it's not the only thing at play. The reason I say that is the simple fact that my 7.2GT3 Mezger, along with every other N/A Mezger, smokes occasionally on startup and there are no turbos present. The reason you get occasional smoke is the fact that oil sometimes seeps past the piston oil rings and makes it into the combustion chamber thus smoking on start up. Whether one has cats or no cats on the exhaust makes zero difference. The piston oil rings are free to rotate about the piston and when the gaps in all three rings line up at or near the 6 o'clock position, It allows the oils to seep past. All Mezgers do it. Well, I would say almost all. I've never had it happen on my 4.0 race Mezger but that engine uses a different piston design with rings that may not be susceptible to this like the OEM rings. During assembly we rotated the gaps to be 120º apart and the rings apparently do not have the propensity to rotate like the OEM rings. Just my $0.02.
The occasional smoke at startup is nothing you can fully get rid of and is part of the Mezger charm, along with the chain rattle you get after the car sits for a while. Well, there is a fix for that actually which we stumbled across.
My '04 with 39K miles will do it occasionally. I doesn't matter if I start it every day, a few times a week, once a week or once every 2 weeks. I've had it smoke two days in a row of the first start of the morning. Then maybe not for 10 or more cold morning first starts. Totally random. As a motor builder of over 50 years and a vehicle tech still working full time, I don't care. If it it did it with increasing regularity and was getting worse, I'd look for a problem. I'm convinced it has to do with being a boxer motor. As I remember I had a BMW motorcycle that would do that too on some start ups, not all.
05-25-2023, 03:06 PM
Smoke on Startup - Solution Found?
