Smoke on startup

[stlrj]

Everone seems to agree that it's normal for the 911, but how come 914 1.7 and 2.0 engines do not smoke on startup? They too have horizontally opposed air cooled engines.

My thoughts are that there must be a problem with the 911 that prevents the proper seating of the rings or even the premature wear.

I also cannot see how so much oil can pass the intake or exhaust valves to cause so much smoke. But the evidence appears to point to whatever is causing the ring sealing problem is also responsible for the premature failure
or wear of the valve train.

What got me thinking on the subject again when I noticed my 911 stopped puffing for a week now...very unusual.

Joe

86 Carrera

[Mike Juzenas]

And how about Subaru's? They have used boxer engines for a long time, and my friends never ever smoked.

[J P Stein]

My own personal opinion is:

In the 911 engine, the oil drains back into the sump to a level highter that the bottoms of the cylinders, then leaks by the rings.
I admit to having absolutly no proof of this.

The 914 and Subie engines are wet sump and the oil level never gets that high.

JPIII

[RarlyL8]

The 911 engine is the only boxer engine in the bunch that has a dry sump oil system.
When and how much the motor smokes upon startup depends on a couple of things.
One is the position of the pump upon shutdown. Some possitions allow more backwash of oil.
Another is the length of time the car is shut down.

[Clark Griswald]

My observation is that if the car is going to puff on startup, then it doesn't matter how long it sits. Could be 5 minutes or 5 days. Same size cloud of bug spray. It seems very much dependent on the position the engine has stopped in, could be the oil pump, I always assumed it was the valves.

On my '77 this happens in probably 1 out of 7 starts.

I have come to appreciate the puff since it only seems to happen when there is a hot babe nearby. The puff alerts me to her presence in the unlikely event that I didn't see her myself.
-----------------
Chuck Moreland '86 Cab - "Sparky", '77 Targa - "Sweet Pea"

[stlrj]

And how about the Boxter and the new 996?

Has anyone heard of these engines puffing?

Joe

[Doug Zielke]

I concur with Chuck. The BB puffs about 1 in 10 starts. It does not seem to have anything to do with how long the motor sits. I worked on it last winter for 2 months, and it did not puff on start-up after all that inactivity.

This occasional "puffing" is not to be confused with the kind of smoking you'd get from a motor with worn-out guides etc.

My local "expert" wrench says it has to do with how the rings and pistons come to rest after running. In other words, it's a mechanical lottery.

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'81 SC Coupe (aka: "Blue Bomber")
Canada West Region PCA
The Blue Bomber's Website

[stlrj]

But how come VW's lack the mechanical lottery ? Shouldn't they puff intermittently too?

[BRAINIAC]

Well the dry sump is the one big glaring variable here. That's got to be it. Wet sumps have plenty of room for all the oil after it drains back. Dry sumps don't.

I wonder if you let the car idle until the oil level on the dash reaches it's highest point, this will put as much oil in the tank and less in the engine. Maybe doing this before shutting the car off every time will reduce smoke on start-up.

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Tyson Schmidt
72 911 Cabriolet
92 C-2 Cabriolet

[stormcrow]

Before I rebuilt the engine in my 78 911 Targa, it didn't smoke. After the rebuild, it smokes on startup - only after it has been sitting overnight. After the engine is warmed up and running, it doesn't smoke. On some occasions when it's cold, it doesn't smoke either - go figure.

Steve

[Doug Zielke]

Originally posted by BRAINIAC:
I wonder if you let the car idle until the oil level on the dash reaches it's highest point, this will put as much oil in the tank and less in the engine. Maybe doing this before shutting the car off every time will reduce smoke on start-up.

Only problem with this, is quite a bit of oil still drains back into the sump. It finds a path through the oil pump, given enough time.



------------------
'81 SC Coupe (aka: "Blue Bomber")
Canada West Region PCA
The Blue Bomber's Website

[RarlyL8]

Joe - my guess is that the Boxster (OK I spelled it right this time) and the 996 won't puff the obligatory.
Why? Get ready to flame away - they don't have dry sump oil systems. You read correctly.
The systems on those cars are considered semi-dry. They call it a large sump, I call it an oil pan. Information came from B.Anderson.

[movin]

Drained my oil(cold) the other day after the car sat for about a week. The engine sump had about 5 1/2 to 6 quarts in it! about 5 quarts came out of the tank. Seems likely this much oil in the engine sump could produce the smoking we see. Maybe the level would still be below the cylinders but the crank would be dipping into the pool of oil, slinging it all over the cylinders until the level dropped.

[This message has been edited by movin (edited 07-29-2001).]

[JDaniel]

I thought I read a post/article about Boxsters smoking on startup... apparently some do.

My car seems to let out the start up puff if it's parked with the nose lower than the tail.
The amount of time parked doesn't seem to matter. I can start it up after 10 days of sleep and get nothing, or I can fire it up after a quick run into the store and cringe as the little cloud drifts by.
I can go through 10 or 20 startups with no smoke, but just when I'm convinced that the fix-it-elves have paid me a visit... cough cough!

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Dan Tolley
1987 911 Coupe
http://www.cheaterswayside.com/911/gallery.asp?sort=0&userid=294

[stlrj]

If all that excess oil sitting in the crankcase is what is causing the smoke then my engine should smoke like crazy because I purposely overfilled my engine with oil to provoke it and it still does not smoke.

What I mean buy overfilling is that I have so much oil in the tank that my gage will register full while I am driving so I assume my crankcase must be at or over the cylinders after I shut off the engine overnight.

Still no smoke...how can that be?

Joe