Dan J.

Hi,

I'm interested in some input on this issue, and I've done some searching on this board already. I found one similar discussion thread from early 2005, but it wasn't resolved.

Since then, maybe someone has dealt with the same problem.

Condition: '86 Carrera with 180k miles. I am missing the records from previous owner between 55k through 130k miles, so it is unknown whether it has had a top end rebuild during that time.

It uses around 1 Qt of Kendall 20/50 per 1,000 miles. I'm not sure how much of that oil the car is burning as there's a small leak from the engine oil cooler (I'll be fixing this during the next tune-up) and it had a small leak from one of the timing chain covers (I put on new seals a couple weeks ago, which stopped that leak). The current oil cooler leak is pretty minor, a drop on the garage floor every couple days, and the bottom of the motor has a little oil gunk at the cooler and bottom oil hose connection. The top of the motor (oil therm, breather) is dry.

My shop always does a compression test as part of their tune-up service and the results are always very consistent. The last was performed at 169k miles and resulted in 170lbs in all 6 cyl. From what I know, the motor is all stock except a SW chip and GHL exhaust and seems to run very strong. I run both a cat and cat bypass (for DE use) and that doesn't really influence the amount or density of the smoke.

The car never smokes on startup when cold. Beginning last summer, the car would occaisionally (1 instance every 1k miles or so) emit oil smoke when warmed up. This was noticable when sitting still, although it's likely to have smoked when moving as well, just not easily noticed from the driver's seat. This smoking happened in isolated circumstances, independent of oil level (on dip stick) and only when the engine oil temp was above the bottom white level on the gauge in around town stop/go driving.

A year later (since mounting the new GHL exhaust), the car now smokes more often, although not consistently under the equal conditions (temp, oil level, type of driving).

This leads me to think that it's an oil leak somewhere that might be getting into or on the heat exchangers, or somehow the car is ingesting oil from the tank. Would worn valve guides or piston ring issues result in inconsistent smoke? Or, maybe the motor is ingesting oil from the tank somehow?

The only consistent factors I have been able to measure is that it only happens when the car is somewhat warmed up, and I only notice it when at idle. I drive the car every day to work 14 miles each way, almost all highway. The car almost never smokes at idle after driving that 14 miles to/from work.

I just pulled all the plugs to look for clues, and they are all dry and a consistent gray/tan color with no obvious signs of oil burning.

I'm about to do the next 15k service (cap, rotor, plugs, fuel filter, valve adj.) a along with an oil change (I change at 3k miles), new plug wires and I'll also pull the oil cooler and replace those 3 seals. I'll also do another compression check.

What else should I be looking for? Many thanks in advance for input.

Dan J.

ked

dan,
one possibility: sometimes an oil return tube will leak intermittently before it goes into total failure mode & becomes obvious. can vary depending upon season & engine thermal cycle. it may drip onto the exhaust, so oil disappears & there is occasional oil smoke, but no oil dripping to the floor. good luck (sounds like you gat a pretty solid 911!).

theiceman

I guess the first thing you need to determine is your definition of "Oil smoke" ...Are you talking about out of the exhaust pipe ? ( burning in the engine via rings or valve guides ) . Or by external source such as an exchanger ... external leak caused by ... well.... just about everything you can imagine ... If it is doing it at idle you should be able to tell this .

But IMO 1qt every 1000 miles is HUGE . I used to have a 944S like that and it turned out to be the oil scraper rings. I think personally you are burning it internally as 1qt every 1000 miles would leave a huge pool on your car or in your driveway in very little time. renenber it only takes one drop on a hot exhaust to make a fair bit of smell and smoke so I would think internals.

Just hac=ve a question out of curiosity.. does your car rpm start to stumble or idle lower if you take the oil filler cap off? if so don't worry it is suppose to.

ked

"But IMO 1qt every 1000 miles is HUGE"
however, in the opinion of Porsche, it is acceptable for an air-cooled 911.
in general though, oil consumption (like fuel) is meaningful when the rate changes suddenly.

theiceman

KED
I do understand Porsches numbers but it does raise a good point , Marketing claims and reality often differ. Great point to start a poll on ..

In 5000 km I have burned 0 oil I use Castrol 20w/50 and do not track the car.

Dan J.

Thanks for the input.

Yes, the smoke is propelled out of the exhaust, it doesn't just form around the general area of the heat exchangers, and yes the idle does go up or down slightly (can't remember which) when you take the cap off the oil tank.

The reason for posting this issue is that 1) it doesn't happen all the time but it's annoying and has me wondering what's up, and 2) I would like to think that it's oil being ingested through the intake or dripping onto or into the heat exchangers and being burned...but only under certain conditions. That's something I can likely address without tearing into the motor...I'm still saving my pennies for that inevitable day.

As for consumption, I've always heard that it's time to be concerned on a 911 if you are using (not leaking) more than 1qt every 750 miles. Maybe a little off the subject, but I had an Audi where the user's manual wouldn't even say what consumption should be, just that it varied by car and to check oil when adding gas. Also, I have heard that some of the BMW M5 V-8 & V-10 motors really consume oil...even when broken-in and in perfect operating condition.

Many thanks all,
Dan.

pojefferson

Dan - did you every figure this out? I have a 1988 Carrera, ~115,000 miles, with similar (intermittent but annoying) symptoms. I’m still trying to find a repeatable pattern, as it does NOT happen all the time. When it does happen, here is what happens:

- I start the car after a few days of not driving it
- I get the usually short-lived puff of smoke; then no more (right away)
- After idling (or driving) for 5 min, there is some smoke from the exhaust
- at idle; e.g. at stop, the smoke is rather light, but noticeable
- when driving, the smoke is more visible, but not really dramatic
- after driving for 15 min; no more smoke at all; idle or driving

Again – this does not happen all the time.

Once person told me this: "You might have your mechanic do a compression test on a cold and then a hot engine. Given the age of your car the valve guides or rings may be warn enough to let the oil get to the top side of the pistons. When warm there is probably enough expansion of the valve guides to seal off the oil intrusion and hence the smoking stops. The same will be true for the piston rings but to a lesser extent.”

I'd like to get some other opinions....

~ Philip

old man neri

Is there any oil or greasiness on the rear of the car such as the licence plate or the bumper? I have an oil leak, one that had gotten pretty bad in the last few days, and it makes a mess of the back. It also smokes, a lot, when coming to a stop and idling. If you had a leak that was occurring while driving it might get blown and swirled up onto the bumper but then leak straight down on the exhaust while at a stand still like mine. With the engine shut off it leaks nothing. Just a thought.