Thanks for that. My 951 is an '89 as well. I've determined that it's using right at the spec limit, set by Porsche and mentioned by you. So I'm not terribly worried. But I do have to keep an eye on it because if I'm driving with a heavy foot it will consume a bit more, which I understand is common. But still my preference would be to consume less than it's consuming now. I'm just trying to understand the most likely source for consumption, so I can properly maintain this car. I don't want to go digging, or have a mechanic go digging, down the wrong path.

Driving with some 944 buddies, they don't see any blue smoke coming consistently from the back. Perhaps a puff when I put it into full boost. Then now I see a bit of blue smoke that burns of as I'm warming the car up. I think it has to do with the thinner oil. But that's pretty much what I've observed. So my question remains, where's it going?

I have not opened the intercooler. But I have noticed a residue around the JBoot area. Wondering.

So if there's oil in the intercooler, turbo rebuild? A little blue smoke on start up, valve seals? What are the symptoms for the AOS seals?

BTW...'87 Diamond Blue Coupe, untouched....gone but not forgotten.

 

If you are planning to only use the turbo during the summer and fall, next oil change I would try a heavier viscosity of oil or switch brands and see what changes.

My guess on full boost it is moving past the rings and seals with the stated mileage.

( I have a set of the Diamond Blue Metallic wheels off an '88 Convertible whose owner no longer wanted them. I have them mounted on a Zermatt 944 until I find the right Jubilee / Celebration 911 to put them on (-; . I have always really liked that shade of blue, as it is so much more purple and much lighter than my Venetian. They look good contrasting each other when I have placed mine next to one .......)

 

Now that I've spent all day reading about oil on every forum imaginable, I've decided to go with Mobile 1 15w-50.

Why?
a) I'm sick of having to order oil off the Internet rather than picking it up at the local employee owned, fair wage offering, retail outlet.
b) It looks like it has enough ppm of ZDDP at least according to this spec sheet.
c) Heavier viscosity as suggested in prior post. Curious if it will temper blow-by or whatever is happening to the vanishing oil in this car.
d) Although I'm worried about wear during cold starts, I will not be regularly driving this car in the cold winter months. A few times perhaps, but definitely not daily.

I'll report back.

 

c) Yes
d) What are you worried about? 15w-50 has a pour point of -39*C.

 

My '89 turbo used to smoke on cold starts for a minute or two every morning (the neighbors were thrilled...). when I bought it the PO had been using some cheap Quaker State 10w-30. I switched to Valvoline VR1 20w-50 for the higher ZDDP and while it ran smoother and seemed quieter, it still smoked every morning. I switched again, this time to Valvoline VR1 synthetic 20w-50 (which most Advance Auto's keep in stock BTW), and the smoking is all but gone. It also consumes less oil between oil changes. It used to use 1.5-2 quarts between changes, now less than a quart. Its been about a year and so far so good, oil consumption has remained steady.

 

Wanted to follow up on this thread and post a few more questions and evidence, so to speak, on what may be happening to the oil. I haven't been driving the car for several months now. It has fresh 5W-50 Mobile-1 in it. That's what I ended up settling on. I may go to Mobile-1 15W-50 for the next change that will no doubt be this summer after spring driving.

At any rate, my plan was to investigate a bit further as to the oil consumption. This is what I know:

• Leakdown compression numbers are 4% - 9% - 2% - 3%. 140psi across all cylinders. Tech remarked on the 9%, but noted it was within range.
• On immediate startup, there is very little smoke but after the car is warmed slightly, at idle, and I rev the motor the oil begins to burn off, and the exhaust can be pretty thick, until it does burn off. It takes about 30-40 seconds or so, if that.
• When putting it into full boost, an observer noticed no blue smoke, but did detect slight amounts of blackish smoke.
• On hard of the gas deceleration, no blue smoke detected.
• Recent spark plug change, after purchase, the tech said the plugs were fine, except #2 looked like it might be running a little lean.
• There are no oil leaks.

I took the intercooler off and made some observations. One side was fairly dry. The other not so much. Here's the video and some pics.



Into the intercooler...


Into the intercooler...


Out of the intercooler...


I'm inclined to rebuild the turbo based on things I've read and researched, as well as the oil I found. Does this look like enough oil to warrant a turbo rebuild? Could a worn out leaky turbo cause smoke on startup?

I also understand that the valve seals may be part of the issue as well, but thinking that will be a bigger job. So I'm leaning towards pulling the turbo out and sending it off, check the AOS, then deal with the seals if a rebuilt turbo doesn't curb some of the oil consumption.

 

It is entirely normal for these cars to be wet with oil throughout the intake tract. Oil vapor/mist from the AOS is routed to the J-boot, downstream of the AFM and upstream of the throttle body, for combustion.

That said, your intercooler does not appear to have excessive oil accumulation. From this, I suspect the compressor side of your turbo is not the problem. More than likely, the seals on the turbine side are wearing, allowing [some] oil into the exhaust tract.

Re: oil consumption...the 5w is simply not viscous enough. And the fact that it's synthetic makes it worse. Before pulling the turbo, I would drain that 5w, refill with 15w/20w, and put some miles on the car.

 

Okay, I'll put some miles on it with something more viscous but I thought the 5W-50 would be essentially the same as 20W-50, at temperature. I know synthetics tend to be probe to more leaking past seals, or so I've read.

But further, could the smoke on startup as I describe indicate a leaky seal on the turbine side when the car is sitting? Or is it more likely valve seals? Just want to clarify.

Also, are you saying that the seals on the turbine side can leak and blow oil straight through the exhaust as the motors running without burning? As I mentioned blue smoke is not apparent when I'm in boost.

 

Smoke on startup is usually vavle stem seals going bad.

 

That's what I've read and think is the most obvious. But I've also read that it can be oil in a leaky turbocharger that blows through. I don't know if that's true.

 

The turbo would blow blue smoke all the time if it was bad. Its definitely your valve stem seals if it's on startup. Your valve seals are probably hard and cracking. And if there that bad then how bad are the rod bearings or head gasket?

 

Would bad valve stem seals account for higher than normal oil consumption as well? The thing is there is no blue smoke when I'm driving, even pretty hard, that I notice.

And when I start it and rev it a little, I do notice misting of black soot, oil I presume, at the exhaust pipe on the garage floor. Unburned oil?

 

Yep under boost the pressure will push out the oil in the stem and under vacuum it will pull it into the cumbustion chamber. At idle and heavy decel it's worse, just push the gas pedal and blue smoke will blow out the exhaust. Address the valve stem seals first. Also when the car sits for a while the oil on the stem leaks down I got the combustion chamber. That's why the blue smoke on start up every time.

 

I've looked at a few 951s now and they've all puffed a bit of blue smoke... even one that only has a few K miles on a rebuild puffed a bit at startup.
I know about rings vs valve guides, etc.
How much is really acceptable?
What do most of you see from your cars?

From reading this and other threads, it doesn't sound like it takes a whole lot of smoke to indicate a turbo rebuild either.

Pardon the pun, but trying not to get 'burned' on a deal.
TIA

 

Others can certainly track on this better than I can. Make sure that you get a leakdown/compression test as part of a PPI. That is absolutely essential and will tell you a lot.

What I have come to understand through the process of learning my car is that the type of oil you use does affect consumption. My initial concerns about consumption have been mitigated somewhat by changing to 5W-50 Mobile One. Consumption has slowed to well within range. Turbos do used more oil, keep in mind, especially one with higher miles. It also depends on how hard it's driven.

The reason I isolated the turbo charger as a possible culprit for consumption was that the records indicate that the valve seals were replaced some years ago during a major service. Plus the leakdown/compression test showed decent numbers. And it just didn't have the characteristics of leaky valve seals and rings that I read about. Driving it hard does not illicit any blue smoke.

On my car there is no smoke on initial startup. However, after the car is warmed up, when I rev it, there is a little smoke generated along with some dark soot that appears to be unburned oil. Also, perhaps slightly perplexing, is that there is very little oil buildup in the intercooler or pipes to and from. So, to my mind, the turbo charger might be a bit leaky on the "hot side." That's my deduction.

Get a PPI from someone who knows the 951.