RandalJ

Hello fellow Rennlisters. I bought an '86 Targa back in September (9/11 to be exact - I'm not kidding), following a prepurchase inspection that revealed a somewhat worn exhaust guide on #6.

The PPI place has a stellar reputation, and said that a valve job was on the "horizon", but that I should get another 15k, maybe even 30k miles before the job would be necessary. They said, other than that, the car was one of the nicest mid-Eighty's cars they had seen in a while, and that driveability would not be affected.

So, taking all this into account, I negotiated a fair price, and had my first 911.

Well, early on I noticed a big puff of white smoke coming from the back when coming to a stop at a light. Over the months, I have tried to discern a pattern, so that I could describe it in accurate detail here.

So, here is what happens: When I am cruising along maybe 40-50 mph and come to a stop, a few seconds after coming to the stop, the engine belches out a white cloud. After a few more seconds the cloud dissipates, and there is no more smoke. There is no smoke upon acceleration, at least none that I can see, even a night with headlights behind me. Nor does there appear to be any when I downshift.

The driveability has not deteriorated, and I have even got in a two-day DE event here in Phoenix back in November with no ill effect.

A few other other data points - oil consumption has been reasonable, under 1 qt every 1k mi. The car had 70k on the clock when I bought it and now has 74k. I'm using straight 30wt Castrol (I changed it in late Dec).

Now, believe me, it is hard to face down SUV drivers (including my wife) sitting next to me at traffic lights with the usual utter contempt, when I myself am billowing smoke over the entire intersection (OK, I'm exaggerating - but only for effect), polluting the air and wasting precious mineral resources more than they are.

So, my question is, is this a classic symptom of The Carrera Valve Guide Wear Problem, and will a valve job address it?

And if this is valve guide related, how come I notice it only when the engine drops to idle? I would think that it would smoke all the time, or at least more when the engine is under higher oil pressure, like when accelerating.

I have made sure that the oil level is near the minimum mark when hot, so I do not think it is oil being ingested at the intake.

Could this be anything else beside the valve guide wear?

Thanks

RANDY P

You're feeding it straight 30 wt? your oil consumption seems normal, actually better than some. however that oil should be a 15/40 or even 20/50- I'd switch it before your fear becomes reality. (esp. in Phoenix!)

rjp

quicksilver

"The Carrera Valve Guide Wear Problem" stemmed from a bad batch of guides that went into 87 and 88 Carreras. I don't think that that is the reason for your problem but that doesn't rule out the possiblity that you have a more normal guide problem.

The guides don't have pressurized oil so the oil pressure doesn't come into play. The engine's vacuum at idle will pull oil through a loose intake guide. It is common to see the puff of smoke when starting.

What kind of mileage does the car have and did the PPI say if the worn guide was on the intake or the exhaust? If it is the exhaust I wouldn't expect to see the dramatic cloud but a loose exhaust guide can cause the valve and seat to fail fairly quickly.

Either way you know it needs to be fixed. Winter project time...

Wayne

Bill Gregory

</font><blockquote><font size="1" face="Verdana,Tahoma,Arial,Helvetica,Geneva">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva"><strong>The engine's vacuum at idle will pull oil through a loose intake guide. It is common to see the puff of smoke when starting.
</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">For clarity, however, the puff of smoke on startup has nothing to do with loose valve guides. It's because oil has pooled over night or after sitting for awhile. Many/most 911's exhibit a puff on startup - that's normal. If you want to check yourself if your valve guides are worn, run full tilt in 2nd or 3rd for a city block and quickly let off the gas, if you see a puff of white smoke out the back, valve guides are suspect. A leakdown test can help confirm the diagnosis.

Randal, I would switch your oil, at a minimum, to a weight that Porsche recommends. Some also use the currently approved oils, some don't. The currently approved weights and oils for all Porsches since 1973 are:

Castrol/Syntec...............................5W-50
Mobil 1..........................................0W-40, 5W-40
Sun Oil/Sunoco Synturo Gold.............5W-40
Texaco/Havoline Formula 3 Synthetic..5W-40
Valvoline/High Performance Synthetic..5W-30

RandalJ

As for the weight of the oil, I chose straight 30 wt for a few reasons:

1. The temperature range in the Phoenix area from 40 to maybe 80, now through March, when I expect to do my next oil change. By summer I had planned on straight 40wt (Randy in SEA. we probably won't see 100+ temps or running A/C 'til May at the earliest. Will be on new oil, different viscosity, anyway by then).

2. I was told by one person that multi-viscosity oils become single viscosity anyway over high temp and time.

3. I wanted to go a bit thicker just to see if the minor leaks I have would dry up (they haven't).

I'm not totally set on single grade - I had planned to experiment, and will probably end up with the factory recommendations (though they don't seem to account for leakage some people have seen with the synthetics).

This is somewhat tangental to my problem, though.

As I mentioned, it is an exhaust valve (#6), described in the PPI as "worn and not seating well". Further discussion at the time with the PPI people lead me to believe that I'd be OK for at least another year, maybe much longer, but I was not warned to expect occasional clouds of smoke.

By the way at PPI, compression was 160 on 1,2,3,and 5, 155 on 4, and 150 on 6.

Leak-down was 3 to 4% on 1-5, but 28% on #6. It was at that point that they thought either broken ring or worn valve. They said they needed to rig somethig to provide extraordinary pressure to be able to hear the exhaust leak on # 6, and the guide is what they concluded it to be.

Again, mileage was 70k, and is 74k now. If you mean MPG, I'm getting just under 20 around town.

Thanks again.

Huey58

I use 15/50 Mobil One is my car! If Porsche puts this in all of their new cars, it must be good!

Steve Weiner-Rennsport Systems

</font><blockquote><font size="1" face="Verdana,Tahoma,Arial,Helvetica,Geneva">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">Originally posted by quicksilver:
<strong>"The Carrera Valve Guide Wear Problem" stemmed from a bad batch of guides that went into 87 and 88 Carreras. I don't think that that is the reason for your problem but that doesn't rule out the possiblity that you have a more normal guide problem.

Wayne</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">RandallJ, et al:

Porsche has continued to use that soft valve guide material in all of the 3.6's and even the 996 GT-3R's so this problem is not just a "bad batch".

Each and every 3.2 & 3.6 911 engine is subject to premature guide wear rates that should be addressed based on oil consumption.

Lastly, leakdown testing cannot show valve guide wear, the only way to see that (aside from high oil usage) is by removal of the valve covers and checking how much the installed valves & springs move laterally in the guides.

Leakdown testing can help quantify cylinder leakage at the rings and valve seats.

RandalJ

Steve, if I remember correctly, they did a valve adjustment just to rule out an overly tight valve, giving the high leak-down reading on #6, but the results did not improve. I do not remember whether they wiggled the valve stem to confirm, but they did hear escaping air through the exhaust when they put high pressure into the cylinder. So their conclusion was at least a bad seating exhaust valve on #6 rather than any ring problems. So, I do not know whether a worn valve can be the direct cause of a seating problem, and therefore SOMETIMES be detectable via a leak-down test.

In any case, would white smoke after a few seconds, and just for a couple of seconds, at idle at a traffic light be indicative of a worn exhaust guide, bad seating of the valve, or both?

If it is a direct result of the seating, can bad seating occur intermittantly? I am not seeing the smoke EVERY time I stop at a light, but more often than not.

I tried Bill's suggestion late in the day, having my wife follow me to look for smoke. Strangely, there was some smoke after the first block (engine cold), and none after that for several more blocks. And none this AM on the way into work. Saturday, during a couple of lengthy drives, it would just billow pretty consistantly at each stop.

My original question was whether this was a typical or "classic" symptom of worn exhaust guides or seats, or whether I could have another problem in addition to the known one.

And one other question comes to mind - I know from my VW days that a tight exhaust valve can lead to a burned valve, which can lead to projectiles and expensive repairs. Would a valve not seating properly be as susceptible to burning as a tight valve? The PPI place did not seem too concerned, other than to say we check it again at 85k miles.

Again, they said a valve job may be needed as soon as 85k, or it might not need it until 100k, that sometimes these things don't get much worse for quite some time. Of course, that will also depend on how long I want to live with the smoke (if that is the cause). The wife and I gave up smoking, and I don't think the 911 should have all the fun.

Thanks again.

Steve Weiner-Rennsport Systems

Hi Randall:

If they heard escaping air from the exhaust during the leakdown test, thats a good indication of leaking valves; bad seating.

Smoke can come from worn valve guides (intake & exhaust), worn seals, etc, and what you describe is symptomatic of this. Its one of the "classics".

I've seen valve jobs required as soon as 60K, although the rest of the engine is quite healthy, and provided thats done, these engines last a long, long time.

For reasons of excessive carbon buildup (detonation problems), and insufficient valve cooling on the exhaust side, I do not advise anyone to let this go too long as the consequences can be very very expensive.

quicksilver

Randall,

I would really listen to Steve W. on this. What you are describing is the "Before" part of an exhaust valve failure. When the exhaust guide is loose it is no longer able to effectively cool the valve, plus the seat wear accelerates because the valve is able to move against the seat. The higher temperature increases the wear rate. As the valve and seat erode they will reach a point were the valve will stop touching all the way around. This means that the valve is no longer able to cool itself through contact with the seat. The combustion gases will start acting like a cutting torch on the over heated portion of the valve. At some point the valve head will fail or the valve seat will come loose. Then you will see the "After" part which is what Steve meant by "very very expensive."

I can't imagine why any mechanic would do a leakdown with that high of a number while hearing the leak in the exhaust and not warn you to immediately fix the exhaust.

Still not sure why this would cause the cloud of smoke though. I would think that you would have to have the exhaust guide so loose that your finger would fit in it to cause a real smoke screen. Are you down-shifting and using the engine for heavy breaking?

Anyway, open the bomb up so it stops ticking...

Wayne

RandalJ

To all - thanks for your input. Now I understand why a valve (especially exhaust) adjusted too tightly would be a worse situation, everything else being equal, than a partially seating valve, which at least benefits from SOME heat transfer to the seat.

Still, I will get it checked out ASAP to at least see whether the readings have deteriorated after 4k miles. If they have, I guess it will be time for a valve job.

Wayne, to answer your specific questions, no, I do not downshift except when going around corners or unless I anticipate slowing and speeding up again behind traffic. Approaching a red light, in 3rd or 4th, I just back off of the throttle, and as I get closer, push the clutch in and let it drop it to idle. It is always a few seconds after I come to a complete stop that I get the cloud for a few seconds - if it's going to do it at all. If I gun the engine to clear it out, I get an even bigger cloud.

The weird thing is that it seems to go through spells. Some days it will throw up the big puff of smoke every time I stop (like when I wrote the original message here). But the last couple of days, little or nothing. A couple of weeks ago I saw it CONSTANTLY smoke at idle (I had driven half a block and was waiting to pick someone up, and the engine wasn't quite warmed up). I have not seen it do this since. Seems like whatever is happening is intermittant. And I can't reliably get it to smoke by going ***** to the walls and dropping it to idle - maybe it will, maybe it won't...

RandalJ

Here's a new theory on the smoke: Oil overfill.

I had ruled this out, but based on what I've since read in the archives (about smoke when braking), maybe I am checking the oil level with the engine not warm enough.

For the oil and filter change about two weeks ago, I filled it with eight quarts, ran it briefly, and added about two more. I ended up with the level about 30% of the way between the two markers, with the running engine fairly warm, around the first marker in the temp gauge.

Prior to that, I was topping it off at that level.

I am going to check to see where the level is when the engine is much hotter. I'm guessing that by now, I have burned some oil, and the level will be down to the lower mark when warm, and maybe to the mid-point when hot - but I might be surprised with an even higher reading.

Do any of you know at what level on the dip stick it becomes POSSIBLE to suck oil into the air intake? Would the level necessarily have to be above the high marker?

This would at least explain the intermittence of the smoke. I may have been boarderline overfill, and the warmer weather up to Sunday may have made the difference. And having burned some of it off, with cooler temps now, it may explain why I have not seen the smoke since then.

The leakdown issue still needs to be addressed, I realize, but the smoke may be unrelated.

Anyway, thanks for your patience and input. I'll let you know what I find.

RandalJ

So much for my new theory. Since my last message, the smoke has returned, though I had not added any oil. That was a few days ago. I added oil yesterday AM, and the smoke was gone. So there is no correlation between the smoke and oil level, nor any particular oil level overfill sensitivity with the Autothority MAF setup.

I have a puff of smoke problem when coming to a stop, which is likely tided to poor exhaust valve seating and a known worn guide on #6, and the smoke comes and goes for no apparent reason.

For all that smoke, I am adding less than a quart of oil per 1,000 miles. Go figure...

Wil R. Ferch

Try different oils first...Mobil 1 15W-50 for synthetic or Shell Rotella-T for mineral oil. Both have helped other hi-mileage cars I came across.
--Wil Ferch

Tom F

Is this valve guide wear problem related to a change in valve stem diameter?