RKD in OKC

Mine used 1qt in 600 miles. Driving fast enough to get a ticket.

Dave928S

+2 on WallyP's comments.

Chuck, my GTS oil consumption follows the same patterns and is stock in all respects. Could be my imagination, but consumption on mine seems to slow a little when it's under 'full' ... that is, it seems to use the first pint or so quicker. I used to be paranoid about keeping it exactly on the full mark, but as it seems to be a little more stable under that mark, I still keep a close eye, but tend to leave it if it's low in the range. Of course I wonder if what I'm seeing is related to less windage at lower crankcase oil levels ... any one else notice that?

If I give it a flogging the rate is about the same as everyone else notes.

polecat702

Sorry if this is off topic, but my 87 never use's a drop between changes. Is this something only the later GTS engines are prone to use oil?

jorj7

Stock early GTS engines use a lot, later use less, but still more then a S4. At least
from what I've read and seen with my two cars.

Jim M.

Mine uses a quart in about 1000-1200 miles of daily driving at little more than highway driving. While on the 3rd Coast pre run and then the tour the next day hitting triple digit speeds and going to red line many many times I used 2.5 qts for the total of 850 miles. Never saw any smoke out the rear view mirror but as Herman said mine does puff on acceleration.

Oh Chuck, your tour group complained you never got over the speed limit. :-)))

blown 87

My rebuilt S4 uses a Qt about every 750 miles, at about 35,000 miles.
I drive it hard, lots of high RPM work, and it is a manual.
When it was a automatic, it seemed to use less.

77tony

Rode up to 3rd Coast from Rockport; 257 miles each way. Fun run approx 170 miles. ? So that's 257 + 257 + 170 = 684 miles. Did not burn a drop of oil this year. I checked the oil level when I left, while I was there, and when I got back. Last year, almost the same route and I burned one quart ? I used Mobil 1 15-50 both years. 77Tony

Gary Knox

Tony,

Your '94 (#155) and my '94 (#156) must have had the same engine building team. Mine has a small leak from the RMS, but even then, is only ~1/2 qt low between annual changes (~2500 miles). My odo just turned 80K.

Gary--

GregBBRD

I learned so much, running Andys' engine on an engine dyno, about the 928 oiling/breather systems....it's really hard to know where to start explaining it all. However, I can tell you this: The stock "late" GTS breather system worked very poorly and literally "pumped" oil into the intake system.

I had always thought that the "lack" of oil return holes in the GTS pistons had to be a mistake....now I realize it was intentional.

Obviously, Porsche "gave up" venting the crankcase anywhere but through the return holes in the cylinder heads in the late model GTS vehicles....that tiny little restricted hole in the upper part of the filler neck is more of a "burping" hole than a true vent. However, Porsche had certainly run enough of these engines on the dyno to know that at high rpms, the head drains were overwhelmed and became plugged with oil. The result, on pre GTS engines, was for the two ventilation hoses at the base of the filler neck to become overwhelmed and filled with oil which actually had crankcase pressure pushing it into the intake manifold. These engines always have the inside of the intake manifold filled with oil.

Porsche had to know that that there was no way to keep the heads from filling up with oil, without actively removing that oil (like I did on Andy's and Rob Edward's engines), but also realized how complex this kind of system would be (costly and complex), so they simply decided to give the oil/vapors more ability to move around inside the crankcase (adding additional "paths" between the cylinders) and "gave up" on venting the crankcase through the filler neck area.

They decided to leave out the oil drain holes in the pistons, because this would have allowed the crankcase pressure to "push oil" backwards through the oil return holes and forced more oil onto the cylinder walls, instead of removing it.

Bold engineering...it just didn't work. The heads still filled with oil and prevented the crankcase from breathing. This continues until the crankcase pressure builds high enough to "burp"....and this "burp" pumps oil into the intake system.....worse than the "pre" GTS engines. Since the 928 GTS had very sluggish sales (worldwide recession in 1994), I'm guess that Porsche decided to cancel the 928 production and thus decided to cancel any engineering work/changes on the final few vehicles....pretty tough to find many changes between the '94 and '95 models....

I found that I could "remove" the excess oil from the cylinder heads and keep all oil from getting into the intake system (Andy and Edward's engines)....but this is complex and expensive. It is also really only needed on engines that are run at high rpms for long periods of time...such as found in some racing events and found in some countries where there are roads that allow extended high speed running (Germany's Autobaun.)

The rest of the 928 engines seemed like they would benefit from a major design change in the the crankcase/intake ventilation system. I've done this, on my "next" engine design. The heads will still fill with oil, if the engine gets run for extended periods of time at high rpms, but the crankcase and the heads can now "vent" without pushing oil into the intake system. Yes, there will be still oil that isn't removed from the cylinder walls, on the GTS models that don't have the oil drainback holes drilled in the pistons, but this system is the absolute "best" that anyone will ever be able to accomplish, without disassembling the engine.

I do use the "Mann Pro Vent"....much like DR did with his "Sharkvent" system....but I took this many steps further, with several design changes to the crankcase and cylinder head ventilation system. Valve cover and intake manifold removal is required....so this is not a "simple" solution....however it has never been a "simple" problem.

Other than the "Mann Pro Vent", all the other hoses are stock 928 pieces....so this system looks very much like it "belongs" on the 928 engine....which was a major design requirement, for me. I had an engine at "Sharktoberfest" that was equipped with the "basic" pieces of this system....sans some of the details....but if you can find someone that took pictures of this engine, you will see how carefully I've made this system look "like it belongs" on these engines.

blown 87

Greg, will your new system be available for sale for use on existing engines?
Guess on costs?

Dave928S

+1 ....

Greg ... I've already PM'd my interest re this solution. My next job on the GTS is intake refresh and PC covers, intake etc .... I definitely want to deal with this issue when I do that, so put me on the list.

Lizard928

Greg,

You saw my "rough" installation of the vacuum pump on my car.
I believe that this could be made to look like it belonged without too much trouble.

If you are going to be testing another engine on the dyno, I would be interested in having you test this type of setup to see if it is able to control the problems you saw.



Also worth noting is that with this vacuum pump installed, with the turbo install, my oil consumption actually went down.
I believe my valve stem seals are needing to be replaced, and now instead of vacuum, there is pressure there. Thus preventing the oil from getting through, as well as less time spent at WOT due to jail time.....

GregBBRD

Yes, interesting application and solution. Certainly worthy of further research and testing.

I think all the talk about "bad" valve stem seals is "urban myth". I'm not sure I've ever seen a bad "viton" valve stem seal, in a 928 application, where valve guide wear is minimal. I've certainly never seen any "coking" on valve guides and stems, burning of the oil around the valve spring, or even oil in the exhaust ports....all common signs of valve stem sealing "issues". For a viton stem seal to leak, the valve guide to valve stem clearance has to get huge....and even then, oil consumption isn't the issue. (993 engines, with their "well known" valve guide wear issues, are the "textbook" example of this.)

GregBBRD

Certainly. Pretty simple retrofit, with the intake and valve covers off. My "current guesstimate" for the pieces is in the $900.00 range....but I'll need to find someone to ecconomically make the "custom Y" pieces that I hand made from billet, for this application, in order to achieve this price. If I have to "hand create" those parts....the price will be significantly higher. I'm also going to have to find a good source for additional valve cover "elbows". Those things are getting expensive from Porsche!

Lizard928

Greg,
I know that my car was pulling in some oil from the valve stem seals.
But then again I have 239k miles on it and know that the heads could use a freshening up as it were.

Your current guesstimate is a great deal cheaper than I was expecting........