PHIL928

I didn't want to hijack the other thread!

I consider this to be quite an extreme case as she uses about 1 quart every 300 miles.

I've tried a provent setup, according to the 928 specialist diagram and it didn't work at all. The provent stayed dry... and the oil consumption remained the same.
The next step was to redirect all hoses from crank case to the provent. This still made no difference, provent still stayed dry.

So after letting the car stand for about 2 months I pulled the sparkplugs and checked for oil in the cylinders using a boroscope, cylinder 7 had oil in the combustion chamber, I'd estimate about 2ml, enough to form a small pool on the lower side. The other cylinders were dry, although very sooty.

I consulted with our local 928 specialist who said that this follows the symptoms of a bad valve seal.

I'd like to get your opinion on this matter, and what the best way would be to proceed.
Does one have to remove the head to access the valve seal or is it something that can be done from the top with the piston at bdc for example?

The VIN for this car is: WP0ZZZ92ZPS800481 which I think makes it an early '93?

Your input is greatly appreciated!

James Bailey

Valve seals and/or worn valve guides is not a common 928 engine problem.....especially at such low miles. Have you had a compression and leak down tests done ? I would suspect that you have problems with the rings and bores.

ROG100

Who cares - isn't oil free in Dubai?

Drive the crap out of it and use plenty of Techron (or equivalent) in the gas. Sitting is not a good thing.

What ever you do please do not mention "vacuum".

GregBBRD

Well, here's the summary of the other thread, in a nutshell:

You do care about oil consumption....the oil in the intake manifold reduces the effective octane of the fuel and increases carbon deposits....both of which are hell on rod bearings.

I've NEVER replaced a set of valve stem seals, as a separate job. NEVER.

The stem seals are made out of Viton, which virtually never deteriorates. And getting enough play in the guide to allow oil to seep around the edges of the stem seal is unheard of.

Only "con men" replace valve stem seals, as a separate job.

Improve the breather system. Getting the crankcase to breathe is the whole trick. Give the rings a chance to re-seal, once you get the crankcase to breathe. Use some Swebco 502 in the oil to help "free" the rings up....they may be very "stuck". You may have to do a little bit of maintenance and clean the Provent element until the rings are re-seated.....just use common sense. It is designed as a filter....and like any filter, may require some maintenance!

If you are going to use a vacuum pump, order new pistons (with pins and rings) now, while they are still available....these engines were never designed to have a negative crankcase vacuum!

Lizard928

Greg,

Give it a damn rest.

Phil,

I would firstly be ensuring that there is no cylinder bore scoring. As well, do a leakdown and compression test to ensure that there are not larger problems!
I also couldn't see the stem seals allowing that much oil to get past them. The pooled oil is getting past the rings. You can remove the fuel injectors and be able to see all the intake stems which will show if any are leaking. The stem seal material does wear, and does harden over time/miles which does reduce their effectiveness.

Don't use the ProVent, it is a crap separator which is easily overwhelmed.

Run a good oil which has good detergents in it to help free any crud from the ring lands. Swepco 502 is a good product for this.

Vilhuer

There is no such thing as early or late '93 MY VIN in ROW cars. There weren't any M718 option cars made for ROW markets. They are all just '93 MY. Some made early in MY and other late, yours is little past middle point meaning possibly in February 1993.

PHIL928

Haha, that perk was given up when the British gave the country back :P

One of the main reasons for solving this problem is to be able to efficiently sharktune the car. Cylinder 7 and 8 knock excessively compared to the other cylinders, so I'd really like to sort out this problem before I do any more driving.
About 30 knocks under hard acceleration, compared to maybe one or two spread across the other cylinders. So you're absolutely right about the oil reducing the octane level, it is clearly seen in practice.

I should have added that I did do a compression test with excellent results ranging from 200-210 psi. I haven't performed a leak down test so that's what I'll do next on the dodgy cylinder 7.

It seems like my attention should be diverted from the valve seals to the rings and bores. I'll get some boroscope pictures!

I will also try the swepco additive.

The reason I ask is to try and figure out whether or not I have the improved con rods, but if it's February 1993 then I probably have R1 con rods right?

Thanks again for your input! You guys are awesome!

69gaugeman

I have also never seen a valve stem seal leak. Unless the valve guides are that worn that they stretch the seal to allow oil past. And you would need a head rebuild at that point anyway. Even then ,there is not much oil at that point unless the oil is pooling. And that would mean the whole head is filled with oil. Not impossible if you are doing spirited driving, but less likely if it is just 'around town' driving.

69gaugeman

Leak down is the only one which will verify ring issues as it is static compression. It determines the size of the leak (they all leak) which is important.What it won't do, however is tell you if the oil control rings are the problem IF the compression rings are good. But a good starting point none the less.

My GT rebuild - ish used the same or more oil than yours. But the leak down was good and compression is good. I removed the cam cover vent from the intake so no oil there, and the spark plugs are clean (it is definitely burning the oil). So the leak down may not show the issue.

siscogts

My car uses oil like my 2009 z4, and within porsche tolerances.

SteveG

IIRC, in a thread here it was stated that November '93 is when the change occurred. Beyond that I don't know a way to pinpoint it w/o physically seeing the rods in one's crank case. I would love a VIN changeover point, but I don't think that exists.

WallyP

The symptoms seem to point at stuck or very worn oil control rings (probably stuck). The "excellent" compression shows that the compression rings are being exposed to far too much oil. This may be a case where an oil additive might actually help.

PHIL928

Well it certainly would be great if all it takes is a bottle of additive!

Should I just add 1 Pint of swepco and see how it goes or should I double dose it?

Vilhuer

There is no VIN change point as its likely change didn't happen in some particular VIN. It happened on particular engine number. Engines with smaller and larger number could end up into bodies in different order. VIN X can have first 2R rod engine while VIN X+n got last 1R rod engine. Best bet is to check actual engine number no matter how old GTS is. First engines to get 2R rods on September 14th 1993 were:

G28/49 85R00533
G28/50 81R50597

This means factory did 32 manual and 96 automatic engines for '94 MY cars with 1R rods before they were changed to 2R. Those early '94 engines were installed into '94 MY cars on some random order. How many ROW and US model cars were made by the time all were used up is not known. 32+96 = 128 is 20% of the model year production of 523 ROW + 120 US = 643 cars. 19 US model early '94 M718 option cars are not included as they are in reality '93 with '93 MY engines and obviously have 1R rods.

Using those production numbers as rough guide first 2R rods could end up in ROW VIN WP0ZZZ92ZRS800164 and US VIN WP0AA292_RS820104. These are not absolutes but should give some idea what is range where new rods came into use.

Chalkboss

I am not one to believe in snake oils but I had a noisy engine, lifter, on my S4 and added Swepco 502 per mfg directions. Noise was gone in a few minutes and after driving for a few hundred the engine overall ran quieter. Stuff really does work, and I think should be added to cars that dont see a lot of use, as was the case in my car before I acquired it.