So why shouldn't I overfill the oil? - 986 Forum - The Community for Porsche Boxster & Cayman Owners

san rensho · 02-29-2012, 05:04 PM

I'm doing my first track day at Homestead Miami this weekend, my car has no oiling mods so of course I'm paranoid about oil starvation. From what I've heard, Homestead has probably one bad section, turns 8 and 9. 8 is a hard braking left hander after a long straight which opens up a bit into turn nine, another left hander.

So what can I hurt by overfilling the oil by 1/2 to 1 quart to hopefully lessen the chances of oil starvation? If the AOS (which is new) gets overwhelmed and I start blowing smoke, I can just call it a day. Or if it happens in the morning sessions, run home, which is close, dump some oil and coma back for the afternoon sessions.

Other than an AOS swamp, is there any other damage overfilling the oil can do to my motor?

Spinnaker · 02-29-2012, 07:02 PM

I am not that familiar with the internal configuration of the oil sump of the Boxster, but in an American V8 overfilling can cause a condition known as oil windage on the crankshaft and oil foaming that can effect the delivery out of the oil pump.

Topless · 03-01-2012, 06:08 AM

Overfilling will destroy your new AOS by flooding it. Fill to the top of your "normal range" on the dash gauge and don't overheat the car. The standard road course should not be a problem. The banked oval/Roval is the m96 motor killer. Have fun out there!

san rensho · 03-01-2012, 03:23 PM

Quote:

Originally Posted by Topless

Overfilling will destroy your new AOS by flooding it. Fill to the top of your "normal range" on the dash gauge and don't overheat the car. The standard road course should not be a problem. The banked oval/Roval is the m96 motor killer. Have fun out there!

Yeah, they are going to run the bank section in the advanced group in thee afternoon. No way I would run the banking.

thstone · 03-01-2012, 05:17 PM

No, don't overfill the oil.

Yes oil starvation is a risk but I ran the roval at Fontana at least 8 times with a stock car and had no problems. A new or novice driver on street tires isn't likely to pull enough G's to make it matter. I didn't worry about oil starvation until I had 20 track days experience and had changed from street to R-compound tires. Of course, your mileage may vary.

Jittsl · 03-01-2012, 05:21 PM

Trust me when I tell you that at your first day at the track you will not be putting your car at any risk from starvation issues. Reality is that pace is not going to be great enough to create the G forces nessesary. I would not even give it a thought until after at least a dozen or more events, you have moved up the run groups, and have shifted to R comp tires and upgraded suspension.

Until then relax and enjoy yourself.

Laurie

Brucelee · 03-02-2012, 04:12 AM

I was under the impression that a dry sump system does not face these issues. In fact, isn't that the one of the points of a dry sump?

I could be wrong.

Brucelee · 03-02-2012, 04:13 AM

AdvantagesA dry sump offers many advantages,[1] the most obvious of which are increased oil capacity afforded by the remote reservoir and the capability to mount the engine lower in the car because of the thinner profile of the sump thereby lowering the overall center of gravity. The external reservoir can also be relocated to another part of the car to improve weight distribution. Increased oil capacity by using a larger external reservoir than would be practical in a wet sump system allows the oil to cool and release entrained gasses from ring blow by and the action of the crankshaft. Furthermore, dry sump designs are not susceptible to the oil movement problems that wet sump systems can suffer from due to high cornering forces. If the oil in a wet sump is forced to one side in the oil pan the oil pump pickup tube can be temporarily uncovered leading to a loss of oil pressure. Because the scavenge pumps are typically mounted at the lowest point on the engine the oil flows into the pump suction by gravity rather than having to be lifted up into the suction of the pump like a wet sump does. Also the scavenge pumps can be of a different design that is more tolerant of entrained gasses than the typical pressure pump which can lose suction if too much air is mixed into the oil. Since the pressure pump is typically lower than the external oil tank it always has a positive pressure on its suction regardless of cornering forces. Another phenomenon that occurs in high-performance car engines is oil frothing up inside the crank-case due to the very high revs agitating the oil. Lastly, having the pumps external to the engine allows them to be maintained or replaced more easily.

Dry sumps are common on larger diesel engines such as those used for ship propulsion. Many racing cars, high performance sports cars, and aerobatic aircraft also utilize dry-sump equipped engines because they prevent oil-starvation at high g loads, and because their lower center of gravity positively affects performanceFrom Wikipedia

san rensho · 03-02-2012, 06:14 AM

Boxster is not a dry sump design, its a wet sump.

Brucelee · 03-02-2012, 06:49 AM

2.4 Dry Sump
PAG claims that the Boxster engine has an "integrated" dry sump, yet there is only one drain plug and no oil reservoir as on 911's. The instrument panel gauge and the dipstick read from the same source. There is an oil pump in each of the camshaft housings for oil return. The biggest difference from the 993 dry sump is the sump is located within the engine block on the Boxster rather than beneath it as in the 993. The sump, by definition, is the bottom of the crankcase where the oil flows to and collects after being pumped over whatever surfaces it was intended to lubricate/cool. The 993, and every 911 before it, uses a scavenge pump to pull out the oil as it flows into the sump and pump it into a holding tank under the right rear fender on all but a couple of early model years. Hence the term "dry sump;" oil is not allowed to sit in the bottom of the crankcase and so the sump remains (conceptually) dry. The main oil pump takes oil from the bottom of this holding tank and pumps it back into the engine's system of oil passages. The advantage of this system is that it prevents oil starvation during hard cornering. With a conventional wet sump system, high cornering loads can cause the pool of oil sitting in the sump to slosh away from the oil pump feed tube. With the dry sump's large vertical storage tank, you'd have to turn the car upside down to keep oil away from the pickup point. In the Boxster and 996, the tank is integrated into the engine block below the crankcase.

There are two techniques for oil to get from the crankcase to the tank below it:

1.A hole in the wall between the crankcase and the tank lets gravity flow the oil from the sump to the tank. If that's the case, then this is really just a conventional wet sump arrangement with an extremely large and well designed sump. Baffles and walls are designed into the sump to prevent the oil from sloshing out during cornering and the high capacity should ensure that plenty of oil is always available at the pick up point.
2.A solid wall between the sump and the tank prevents oil from flowing between the two. A scavenge pump moves oil from the sump to the tank when the engine is operating.
Both techniques are used in the Boxster. There are two oil pumps that take oil from the cylinder heads to the main oil pump. This oil is fed into swirl pots to be centrifuged and defoamed. There are oil collection channels cast into the crankcase to return oil to the oil pump.

stephen wilson · 03-02-2012, 08:01 AM

Agreed, the Boxster is definately a wet-sump system, with auxilliary "lift" pumps due the the horizontal cylinder configuration. If it was a true dry-sump system, there wouldn't be these oiling issues.

thstone · 03-02-2012, 09:46 PM

"PAG claims that the Boxster engine has an "integrated" dry sump..."

When the oil sump is "integrated" and there is no pressurized external oil resevoir, its a wet sump design, regardless of what the Porsche marketing people say.

Brucelee · 03-03-2012, 04:55 AM

I think we are off topic. The real issue is whether the Box is likely to suffer "oil starvation" and if then, whether overfilling the sump is a good idea.

I would assert NO to both.

maj75 · 03-03-2012, 12:15 PM

You would be wrong in the first case if applied to a Boxster w/ R-compound tires.

Correct as to your second point.

Ghostrider 310 · 03-04-2012, 01:52 AM

It cautions in the Boxster manual to carefully top off the oil and to never overfill. Besides the AOS, I was always told that overfilling causes stresses to all the oil seals.

san rensho · 03-04-2012, 12:19 PM

Well I went on the track yesterday (Homestead in Miami) with the oil overfilled by a little less than 1/2 quart. Nothing happened. No clouds of smoke while driving. No clouds of smoke when I started the car up again before each session but I did make sure to idle the motor for about five minutes after each session before I shut it down to let the scavenge pumps get all the oil back into the sump. Ended up using maybe 8 oz. of oil for the track day, which I think is ok.

I did have a small amount of oil leak from the cam covers, enough to get a couple of spots on the ground, but that has happened to me after spirited driving on the street also.

Only other concern (other than scrubbing off the equivalent of about 5k road miles of rubber off the tires, and significant front brake pad wear) was I had to add some power steering fluid. Not a lot, but it was definitely down.