On my 987

Yesterday the dealer changed the oil (and filter) on my 981 (9A1 3.4L engine. ) At home, with the car parked overnight, I found a fairly significant spill of oil on the garage floor. There was some oil staining around the drain plug, but no dripping was seen even over several minutes. I topped off about 3 ounces, which is nothing unusual, as the fills are always a bit short (better than too much.) With each hour or so park in various places, there was a 3 inch splotch, and once I saw a drip. Also, the oil was clean; and because it was persistent, I discounted it being oil that had somehow spilled and got temporarily trapped somewhere.

So, this morning I went back to the dealer, and they discovered the oil plug had cracked part way around the shaft where it meets the head. The service manager said he was making a report to Porsche, and said there's no service life spec for the plug, so he would make a recommendation.

I suggest a very careful check of the plug each time the oil is changed, and maybe replace it every 10th time or less. Cheap insurance for not having a slow or fast catastrophic oil loss.

I don't think I've ever heard of that happening before. I wonder if it was just a plug with a weak spot. Definitely a good thing to keep an eye out for.

My thought is that the shop over tightened it last time the oil was changed and then cracked it trying to unloosen it for the current change. A 981 is way too young of a vehicle for an oil plug to "wear out." I've had Toyotas that had the 3,500 oil change intervals and had the cars for 7 to 8 years without any issues. You are talking about two dozen oil changes.

Yeah, this is unprecedented in my experience. We always have heard about stripped threads or facets. I'd hate to think a Porsche dealer mechanic, who does this all day long and is likely of a fairly high quality standard, would be that ham fisted. It is possible, but there's also the possibility this particular plug had an undetected flaw. I doubt Porsche x-rays this part (like Ferrari did/does with block castings.)

The oil's been changed, all by the same dealer if not the same mechanic, 6 times so far, I think. Whatever the prime cause of failure, it still would be a very cheap, and very worthwhile precaution to put in a new plug every so often. Then again, what if the new one is defective?

A couple of points I picked up from forums in my BMW Z3 days which might apply here. The plug is purposely designed to self destruct if over tightened to avoid stripping threads in the pan. The right way to tighten the plug is by feel. There is a compression washer which will slowly compress as the plug is tightened. When it stops compressing, it's time to stop tightening the plug. A torque wrench not recommended. Expert comment (Pedro) welcome.

....changing your oil is the same guy washing your car.

They only bill him out at ~ $135/hr

"A mile of highway will take you one mile. A mile of runway will take you anywhere."

"A mile of highway will take you one mile. A mile of runway will take you anywhere."

Grant

gee-lenahan-at-gee-mail-dot-com

at the local Porsche dealer was a very good guy. I hired him and a cousin of his a few times to help me move or help me move my parents. He left the dealership and took a service advisor position at the local Honda dealer. I was there one day and watched/listened to him work with customers. He sounded like he had been an SA his whole life. I was very impressed and told him so.

I found out later he had been detailing cars IIRC with his dad, then became an SA and had done that a number of years, but went back to detailing on his own because he liked detailing cars better than he liked being an SA.

a spare drain plug and would hand it along with a filter, crush washer, bottles of oil etc to the mechanic and got back a filter and drain plug after watching the oil fill. Not that my oil was ever that dirty, I guess I just wanted the drain plug to be clean and oil free when used. I'd clean it myself, inspect the filter and then bag it for use the next time.

The things we will do for our toys.

I debated whether to bring it to my local shop or chance driving 35 miles to the dealer. I couldn't see the filter, but the plug looked well seated, and that's where there was residual oil, so to the dealer it went. I kept an eye on the oil pressure, and at the first sign of subnormality would shut the motor and coast onto the interstate's shoulder. Then the dealer would tow it (under warranty.) Afterward, I joked with them that I always change the oil every 100 miles anyway!

The stock plug is designed to be sacrificial. If it's over-tightened, it breaks before the pan does. Some of the aftermarket plugs are made of a harder material that risks damaging the pan.

I used my original drain plug for 165k miles before replacing it. And that was because I cross-threaded it like a jerk. I've never had any leakage.

A magnet wouldn't do much, but wouldn't be a bad thing, either.



Edited 1 time(s). Last edit at 08/03/2014 09:57PM by Laz. (view changes)

Edited 1 time(s). Last edit at 08/03/2014 09:57PM by Laz. (view changes)

1. the underfil may be correct. Oil should only be at level when warm. Its level rises about 200+ ml in my experience

2. I have never had a plug crack, btu they do distort with time. I have two laying around. I expect it was over-tight. They don't need to be very tight at all, i believe the spec is ~ 30 lb-ft

Grant

Grant

gee-lenahan-at-gee-mail-dot-com

... I've never seen a cracked oil-drain plug.
I've seen that over 50% of them have stripped or semi-stripped the internal hex by using the wrong sized tool.
In my personal car, the only times I have replaced the plug is when I replace the engine
One of my plugs went over 223,000 miles without leaking a single drop of oil.
I do replace the aluminum crush ring every time and I never over-tighten, same with the oil filter canister.
Happy Porsche'ing,
Pedro

Pedro Bonilla
1998 Boxster 986 - 311,000+ miles: [www.PedrosGarage.com]
PCA National Club Racing Scrutineer - PCA National HPDE Instructor - PCA Technical Committee (Boxster/Cayman)

---

Racecar spelled backwards is Racecar

"Racing is life. Anything before or after is just waiting" ... Steve McQueen as Michael Delaney in "LeMans"

"If you wait, all that happens is that you get older"... Mario Andretti

"Being second is to be the first of the ones who lose" ... Ayrton Senna

Edited 1 time(s). Last edit at 08/04/2014 10:37AM by Laz. (view changes)

1. The oil is checked when the engine is "completely" hot, these days meaning at least 194º. I always wait a minimum of 5 minutes after shut off, if not more. Only a couple ounces are added from that point on over a period of maybe 15 minutes, and the fill icon has never gone over the exact full increment. My driveway is a little bit uneven, but I let the car roll into its "natural" level, and at home almost always check it there. The fill icon won't read if the computer doesn't like the conditions, but will let you check, however inaccurately, while the engine is running. I haven't studied the whys and wherefores of those conditions, but I think the manual says the level can be checked after fully warm and the engine has been off for a minute or so. (I allow for a reasonable amount of drain-down time, as implied above.
2. Yes, but I'd hate to think one or more of the dealer mechanics over-torqued the plug. Jeez, I think any of us here have the feel, and respect for torquing aluminum parts. If anything, I think the mechanics are now more conscious of what constitutes too much torque.



Edited 1 time(s). Last edit at 08/04/2014 10:38AM by Laz. (view changes)

it is a sign of uneven stress.

What I believe happened is the tool bit didn't get inserted in the tool bit hole all the way. The fit is quite good and if the bit has any oil on it and it usually does this creates an air piston which produces enough resistance the tech believes the tool bit is inserted all the way to the bottom of the hole but in fact it is not. Then wrench is turned and the drain plug loosens and is removed. But this creates a burr in the tool bit hole which then sets depth to which the bit can be inserted again.

The drain plug is installed and tightened. Because the bit is not very deep the forces are uneven and the cracking can be the result.

Not inserting the tool bit is a rookie tech mistake. (It is a mistake that at least one tech at a quicky lube joint made when I had the oil changed in my Boxster there once.)

In fact i couldn;t really understand why the plug would crack, rather than strip or distort, if over-torqued.

I'm even dubious if the tool is only partially inserted, but it makes much more sense.

As to expecting mechanics to have good feel, see car washing comment above. May not have been a meachanic at all, or worse, one working toward a 1.5 biilable hours ratio.

Grant

Grant

gee-lenahan-at-gee-mail-dot-com

The dealer certainly doesn't want to replace 8 quarts of Mobil 1, lose lift time, have make-good labor charges, and perhaps delay another customer's service needs.

Quote
Laz
1. The oil is checked when the engine is "completely" hot, these days meaning at least 194º. I always wait a minimum of 5 minutes after shut off, if not more. Only a couple ounces are added from that point on over a period of maybe 15 minutes, and the fill icon has never gone over the exact full increment. My driveway is a little bit uneven, but I let the car roll into its "natural" level, and at home almost always check it there. The fill icon won't read if the computer doesn't like the conditions, but will let you check, however inaccurately, while the engine is running. I haven't studied the whys and wherefores of those conditions, but I think the manual says the level can be checked after fully warm and the engine has been off for a minute or so. (I allow for a reasonable amount of drain-down time, as implied above.

I've wondered about the oil "measurement" you get with the engine running. My thinking is that the computer "remembers" what the level was the last time a hot (or fully warmed up) engine was when the engine was stopped. I would think that the oil level would be lower when the engine is running, simply because some of the oil is out of the pan circulating to lubricate the engine. Not sure just how much oil would be involved at any given time. Maybe 1/2 to one quart?

upon the type of engine I guess.

I don't know about the newer model cars with the DFI engines but in my Turbo I can check the oil level with the engine running. In fact this is the only way to check the oil level. There is no dipstick. There is no engine off check oil option.

The engine is a dry sump engine which means all the oil that is not directly in the engine -- in the oil passages, filter, and recesses of the lifters, tensioners, bearing, etc. -- is in the oil tank. The scavenge pumps see to that. Thus the oil level measured is a accurate representation of the amount of oil in the oil tank.

I like the ability to check the oil level with the engine running. This means the oil is hot, at least above some minimum temperature, so if the level is low and oil needs to be added the driver is less likely to overfill the engine with oil as he might if he topped up a cold engine only to then when the engine got fully up to temperature found the oil level too high due to an increase in volume from an increase in temperature.

Maybe there's a LASER ranging device at the top of the sump that's aimed down at the oil. That'd be something!

I can check the oil level anytime, by:

1. not depressing the clutch,

2. then turning the ignition key all the way clockwise (as if to start the engine),

3. then turning the ignition key the full way counterclockwise (off);

4. again turning the ignition key all the way clockwise (as if to start the engine).

The engine oil level is then displayed, unless the engine has recently been running, in which case the display will tell me how many minutes before the oil level will be displayed.

Because the clutch is not depressed, the starter motor does not engage.

(BTW, I always do my own oil changes - once during the summer, and once at hibernation time -, always using a new filter, and crush ring. Although I use a factory wrench to remove the filter housing, I tighten it using only my gloved hand. And although I have a spare drain plug on hand, I've never had to use it.)
.

The sensor tube -- a long thin/small diameter plastic tube -- contains two electrical circuits. The tube fits down through the engine block and extends down into the oil sump or oil tank.

The tube is sealed at its tip but has holes through its walls away from the tip.

The wiring circuits: One is a thermister which is used to measure the oil temperature. A length of insulated wire runs from the electrical connector end of the sensor to the tip of the tube and then back up to the connector. At the very bottom of this tube the wire connects to a thermistor.

The other circuit has an insulated wire that runs down from the electrical connector end a ways then at another solder joint connects to a very fine strand of bare or un-insulated wire with a diameter I just measured to be 0.003 of an inch. This bare strand of wire forms a loop (with the end of the loop wrapped around a piece of nylon to keep the loop strands separate and spaced evenly and stretched out. The length of the loop that is the bare wire is only 1.350 inches long by my measuring.

The wire looks to be pretty tough and consists of some fancy alloy too one that doesn't corrode in any of the acids found in the oil and can withstand the sloshing oil without developing metal fatigue and breaking. I suspect the wire is either tungsten or Ni-Chrome (which is used in toasters).

As this bare wire strand comes up the other side it reconnects to the insulated heavier wire through another solder connector and this insulated wire then continues on up to the disappears into the electrical connector end.

This second circuit is used to measure the oil level.

The circuit with the thermister provides a voltage level signal that is translated into temperature via the engine controller and an analog to digital converter.

For the other circuit a resistance measurement is made by a precise (in terms of voltage level and duration) pulse of electrical power through the wire. This pulse of electricity heats the wire.

How much the wire is heated is dependent upon how much of this bare wire strand is exposed to air (crank case air) vs. how much is submerged in the oil.

A second resistance measurement is then made and with (possibly) the input from the oil temp sensor and a determination is made of the oil level in the engine. A look up table is probably involved.

The oil level sensor readout has 7 segments or bars from low to max.

Say the wire's resistance range is 3 ohms (little resistance) to 51 ohms (higher resistance).

Assume further the reading ranges for the max level is 3 to 9. 10 to 16 is the next bar below max. 17 to 23 the next. 24 to 30 the next. 31 to 37 the next. 38 to 44 the next. And 45 to 51 is the lowest reading.

If the oil level is high, most of this bare wire is submerged in oil and the wire in the oil will not heat up any significant amount so its resistance will be less affected. Thus the reading will fall in the 3 to 9 range. In this case all segments would be lit.

If the oil level is low, a larger portion of this bare wire is in the air (crankcase air) and the wire will heat up more and its resistance affected more. Real low oil level would result in a resistance reading in the 45 to 51 range. In this case then maybe all segments save the min segment would be dark.

As an aside, the above provides a clue as to why overfilling the engine with oil is bad. If the oil level is too high the bare wire is totally submerged and its resistance variation will fall outside of the table above, say it comes to 1. Thus the oil level system knows the oil level is too high but it can't determine by how much too high it is. There is no reason to expect the oil level sensor to have that much range to deal with an overfilled engine.

It is not clear if the temp sensor plays a role in the oil level determination. It could possibly be used to help derive a better more accurate level determination.

OTOH, the air (crankcase air) around the bare wire above the oil is the same temperature as the oil below it so the thermister may not be needed in oil level determination.