freakngeek

Hi Guys, normally I can find answers in the Bible of 928 info here
But this time I have an issue that I cannot find answers for
A little backgound, well a wee novel now

1982 (UK/ROW) 4.5lt, 3 speed Auto, stock standard
Yesterday, thought I'd treat the Mrs and take her out for lunch just out of Queenstown (NZ)
I checked the oil before starting
Thought could do with about 0.5lt
Then had to go to shipping Container I keep bits in to grab the oil in this case Penrite 15w-50, chose this as mornings are -5 or so here at the moment, so 20w-50 a bit thick when so cold
I proceeded to pour some in the filler, noted at time that oil was not going through strainer, lifted this up and slowly got oil down into engine, took more than I though it needed
Now we merrily went on our way, drove over Lindis Pass 971m or about a 500m climb over 32km, all went well, drove to Queenstown (200km from home), drove to lunch (very nice)
After lunch thought go home via Wanaka over the Crown range (1121m), but after the very steep zigzag start which gains about 350m over 3km, the road levels off, but here there came a huge cloud of blue smoke from exhaust
This went on for a minute or so, decided to not go this way as also needed to go back over the Lindis again
All went well, no more smoke until going back up the Lindis
Just before the Pass the road gets steeper, and again huge clouds ot Blue smoke on less steep bit, stopped had a look about, couldn't see anthing, idling no smoke
Drove on for a bit, smoke went away after awhile, then at the steep section nothing to be seen and no more smoke all the way home

Now I've taken all the plugs out and all are clean as a whistle, so any oil well burned away and unlikely to be valves/seals
Oil is down a little from when I filled it yesterday
So I'm little perplexed

I assume some oil ran down the vent hose that runs from oil filler to block when filling and oil not going through strainer
Could this have been sucked back up into the vent hose that runs to air intake ?

Any one else had this ?
Your thoughts appreciated, was rather a tense trip home

Kiln_Red

How long was the whole trip? 400-500km? How much oil did it consume?

freakngeek

All up 450k's I would think, Odo not working
Oil level pretty well back where it began in morning, so about 750ml-ish

Kiln_Red

The fact that the smoke arises during increased load doesn't sound too good to me. I forgot to ask how many miles are on your car. If it were mine, then I would be checking compression and/or conducting a leakdown test. My suspicion is worn rings/cylinders.

freakngeek

Odo not workd for 20 years I suspect its sitting on 68k MIles
But doubt many miles were done over those 20 years either
I've probably done about 2000km in 10 Months, first time I've seen that Blue smoke though have gone over plenty smaller hills
I'll book her in for a good looksy

freakngeek

Had a poke about the Interweb
Am pretty sure the Oil separator is at play here
Oil/air are thrown up into the seperator from crank via opening
Oil spinning around is flung to the sides of the seperator and flows down
Air is sucked back to throttle valve vacuum line
Now I'm thinking that the seperator mesh filter was not allowing oll to flow back in under load fast enough
OIl spray getting sucked into return to throttle valve vacuum port = blue smoke
I could be completely wrong ofcourse and compression could be down, but all spark plugs looking identical leads me to lead to oil in air



Kudos to 928 Motor Sports for insite on how this all works, above taken from
928 Motorsports Oil Control System for the 16V Porsche 928

Kiln_Red

There is a push/pull balance at work with the crank vent system. Higher engine load = higher crankcase emission (push). Lower load = increased vacuum (pull).

One can be mistaken to think excessive oil in the plenum & throttle housing supports a crank vent issue when it can actually serve as further evidence of a ring interface deficiency. Leaking compression rings elevate crankcase pressures.

SwayBar

Do you have oil pooling in the vee between the cylinder heads?

If so, it can slosh out and onto the exhaust during maneuvers like going up a hill.

freakngeek

Ah, yes first thing I cecked at the tiime, no oil at all in valley, confirmed with pulling all plugs and checking around fuel distributor etc
There was a tiney wee wisp of smoke coming from underneath right bank while blue smoke was pouring out the Exhaust at the back of car
I'm still leaning to my Oil seperator being the culprit, when filling oil as thick as treacle not wanting to go through mesh screen (why is bottom solid piece ?) decided to pop into the oil seperator inlet, probably sat here until vacuum high enought to suck it into plenum via filler breather hose

Middle of winter here, just had a heap of snow on hills not very friendly for any 928 work
Don't want to take car into town as dark going and from work, already hit a small horse sized rabbit, breaking off once side of front spoiler
So compression test will need to wait
I'll pull the Plunum off and have a peek in there on weekend, if oily in here then confrims it coming in infront of that

But thanks for pointers

FredR

Many moons ago was following a friend in his 88S4 as we travelled up to Dubai for a Porsche event. The approach to the border crossing has a relatively steep uphill section as we cross the Hajjar mountain range. During a spirited uphill burst his S4 started billowing blue smoke out of the exhuast pipe. I raapidly went past him gestating to pull over. We reckoned he had overfilled the sump with oil and during the uphill section oil then flows out of the sump and onto the floor of the pan and then the windage cloud whips up this oil and hence the Red Arrows impersonation.

Doubtless you have already discounted such and I noted your comment stating "how it took more oil than you expected" so it is possible that somehow you have a corrupted perception of the amount of oil in your motor- false dipstick reading somehow perhaps?

At the end of the day if the motor is original build then 40 years of use does not really owe you anything.

freakngeek

Picture tells a 1000 words, I completely cleaned Intake plenum a few weeks back, today covered in oil (internally) and on/in intake runners
Can confirm, filling oil with strainer in at around zero degC = oil running into Oil seperator faster than going into sump
Then a matter of time before oil being sucked into vent hose which runs into intake

Oil seperator is behind water bridge, as I need to replace broken coolant temp sensor I may just give the entire coolant system a birthday
I'll take oil seperator out and give a clean at same time

nirich

I guess that's relatively good news............better than broken rings etc.
I'll bet the stress levels are down now. Knowing the cause is a large part of solving the problem.

freakngeek

You have no idea how well I'll sleep tonight
The Wife has her 2 kids, I have my Baby

Kiln_Red

Drive another 450km on as flat a road as you can find. You want to see a lot less than 750ml of consumption to support the theory that the oil aeration from the other day was a product of the driving conditions & not excessive crankcase gases. Keep an eye on your hot idle oil pressure.

To be clear, a healthy system should never aerate oil to the extent that 750ml of it can consumed via the intake in any conditions short of a race track... the sort of conditions Carl Fausett targets his improvements around.

Also, the amount of oil entering the separator while running should encounter the same restriction you noticed while pouring the oil, i.e. same rate in/out.

Not trying to kill the mood by any means, and perhaps your experience was merely one-off event attributable to your driving and/or conditions. But, if the separator was suffering from a measurable blockage, then you would hear a hissing sound from the engine.