oil tank overfill

[david.avrahami@]

I found a tiny oil wet spot on RHS of the engine bottom towards the front of the car.
The tiny leak DID not show up again after a 20 minute drive...
my oil filling gauge indicated upper level position...
question: Where is the leak appear when you overfill your oil tank? is there a specific location or wet part that shows?

[darrin]

don't trust the oil gage on the dash, check the dipstick, on a level surface with engine running and fully warmed up. Come back to us for thoughts/next steps if your dipstick registers above the top line.

If you're only seeing a bit of weepage on the bottom of your engine (and not drips on the garage floor), you might want to consider yourself lucky -- minor oil seepage is (imo) one of the joys of ownership of these cars . . .

[david.avrahami@]

It was not over but just at the top line...but assume it was over...an overfill, where will the excess oil show? which area in the engine will show it?
BTW, I did drain some oil (I have a drain valve....great invention), checked with engine warm and running, to bring it to the middle of the measuring dip stick.

[Eagledriver]

Typically there’s a breather line from the tank to the intake housing (air cleaner). The oil goes into the intake system and gets burned by the engine. When that happens you get large quantities of smoke out the exhaust. The oil can also drip out of the intake system.

-Andy

[john walker's workshop]

Might want to put the year of the car in your signature, for accurate answers.

[david.avrahami@]

Forgot to mention...my car is an 87 carrera...thanks John!

[Sunroof]

I have a 1973.5T, but our oil tanks might be similar as far as mounting goes. Anyways, after engine warm up I noticed that oil was dripping down the oil tank and onto the floor. The leak puzzled me. I removed the tank, took it to a radiator shop for cleaning and they discovered that at one of the two mounting brackets (welded onto the top of the tank), a crack developed in the weld. You had to look close to see it. When the oil level came up in the tank from expansion, the oil leaked out the crack. This was very rare and unusual, but I had to figure the tank was 30 years old at the time and vibration plus heat. I had the mount re-welded and that took care of the problem. You might have the same problem.

[Flojo]

leak right front?

well yes, it can be the (expensive) oil cooler leaking. but that is rare

usually it's rather one of the two:
- greater obvious oil leaking: spill from above from the trinity (triangle of death)
or
- a leaking rocker shaft (had that issue, solved with RSR seals)

regarding an overfill, I back darrin: measure when hot and even standing.
should you notice an overfill, you can suck excessive oil with a small hose and a big syringe (did that once myself, happens)

edit: oh, nearly forgot, leak no 4 possibility, but even rarer:
make sure to seal this weak point inside/outside according to porsche bulletin (sits behind oil cooler).

[KTL]

I think the leak and the apparent level on the gauge are just a coincidence.

Like Andy said, when the oil is overfilled the oil tank pukes itself back into the intake manifold. A Carrera 3.2 engine has the oil entering the intake system above the throttle plate via the rubber elbow that connects the air meter to the throttle body. In the elbow is a fitting that has a large hose connected to it, typically called a vent hose. The vent hose runs across the rear of the engine bay and into the oil tank. There's also a second large hose that comes from the top of the engine and connects to the oil tank. The second hose relieves crankcase pressure (and a significant amount of oil) from the engine and is commonly called a breather hose. This pressure forces oil out of the tank via the vent hose, if the level is high enough, and that's how the oil gets puked into the intake elbow.

The whole intent behind this hose arrangement is to relieve the engine of crankcase pressure (caused by the very fast movement of the crankshaft, connecting rods and oil being slung everywhere inside the case) and the oil tank provides the means to do this by acting like a baffle to collect the liquid oil. So the air & oil collected by the tank creates an oil vapor cloud inside the oil tank that is then forced from the tank by the crankcase pressure. That oil vapor cloud is pushed through the vent hose and is then burned by the engine in the combustion process.

You'll know it if engine is severely overfilled because the engine will ingest liquid oil and make a smoke show like you can only imagine. I mean we're talking like James Bond 007 smoke screen out the back of the Aston Martin kind of smoke. Been there, seen that, embarrassed as hell by it right in front of my house. I pulled out of the garage, drove about 50 feet, and as soon as the RPMs rose high enough to force the oil up to the intake, it was a ginormous smoke screen. I immediately turned around, could barely seen anything around me, and headed back up the driveway into the garage with smoke everywhere. Anybody watching must have thought i'd just blown up my engine.

The oil puking was so bad that the oil didn't get fully burned in the combustion chambers and was then spit into the exhaust system. The gasket joints in the system were weeping of oil. I had to take off the entire exhaust system and flush it out because it would have taken far too long and produced far too much smoke for me to tolerate it just burning itself off. I flushed the banana muffler by dumping several doses of kerosene in it and sloshing it around for a long time to dilute/release the oil and rinse it out. What a fiasco........

[Canada Kev]

It's also a good idea to NOT run the oil level right at the upper line on the dip stick. Many of us run the level about half way in between the marks - it's about 1.5 litres from the lower to the upper line. The cars tend to use far less oil when the level isn't that full.

[Alex66]

That's exactly my experience - oil consumption doubles when the level is close to the upper mark.

[david.avrahami@]

Thanks guys...now I understand clearly the overfill process and what should be done to avoid it. I happen to install last fall an oil discharge valve at the bottom of the oil tank. and I used it to take out approx half a litre of oil and bring the oil mark on a warm engine to the middle of the dip stick markings.

[donagain1]

Originally Posted by KTL

I think the leak and the apparent level on the gauge are just a coincidence.

Like Andy said, when the oil is overfilled the oil tank pukes itself back into the intake manifold. A Carrera 3.2 engine has the oil entering the intake system above the throttle plate via the rubber elbow that connects the air meter to the throttle body. In the elbow is a fitting that has a large hose connected to it, typically called a vent hose. The vent hose runs across the rear of the engine bay and into the oil tank. There's also a second large hose that comes from the top of the engine and connects to the oil tank. The second hose relieves crankcase pressure (and a significant amount of oil) from the engine and is commonly called a breather hose. This pressure forces oil out of the tank via the vent hose, if the level is high enough, and that's how the oil gets puked into the intake elbow.

The whole intent behind this hose arrangement is to relieve the engine of crankcase pressure (caused by the very fast movement of the crankshaft, connecting rods and oil being slung everywhere inside the case) and the oil tank provides the means to do this by acting like a baffle to collect the liquid oil. So the air & oil collected by the tank creates an oil vapor cloud inside the oil tank that is then forced from the tank by the crankcase pressure. That oil vapor cloud is pushed through the vent hose and is then burned by the engine in the combustion process.

You'll know it if engine is severely overfilled because the engine will ingest liquid oil and make a smoke show like you can only imagine. I mean we're talking like James Bond 007 smoke screen out the back of the Aston Martin kind of smoke. Been there, seen that, embarrassed as hell by it right in front of my house. I pulled out of the garage, drove about 50 feet, and as soon as the RPMs rose high enough to force the oil up to the intake, it was a ginormous smoke screen. I immediately turned around, could barely seen anything around me, and headed back up the driveway into the garage with smoke everywhere. Anybody watching must have thought i'd just blown up my engine.

The oil puking was so bad that the oil didn't get fully burned in the combustion chambers and was then spit into the exhaust system. The gasket joints in the system were weeping of oil. I had to take off the entire exhaust system and flush it out because it would have taken far too long and produced far too much smoke for me to tolerate it just burning itself off. I flushed the banana muffler by dumping several doses of kerosene in it and sloshing it around for a long time to dilute/release the oil and rinse it out. What a fiasco........

Wow, this was amongst the most well written and informative posts on the forum. Kudos for the non-know-it-all response, it's was very helpful for understanding the maze of hoses to and from the oil tank.

[KTL]

Thanks for the compliment. Glad to share my mistake so others don't make the same one.

Full disclosure here, my oil level wasn't high by a small amount. We're talking several quarts over-filled. I think what happened is I drained only the oil tank but not the engine drain. So there was already a bunch of oil still in the engine that I hadn't drained out and I believe the car had been sitting for quite a long time in the garage. Even though the 911 engine is a "dry sump" there still can be a lot of oil in the engine when it's been sitting for a while.

What happens when the engine is shut off, most of the oil in the system is in the oil tank and external oil lines because the oil pump has been sucking it out of the bottom of the engine and sending it off to the tank. Some oil drains back through that suction side of the pump and there's also a good amount of oil throughout the engine (pressure locations and splash-oil areas) that gravity drains down to the bottom of the engine. There's also some oil that "bleeds" out of the tank and sneaks past the oil pump gears. So my point here is that even though the bottom of the engine is supposed to be mostly empty of oil, a large amount of oil finds its way back to the bottom when the engine sits for a long period of time.

When I refilled the engine with oil, I put in around 8 or 9 quarts in the tank like I always do and then take it for a drive to warm it up so I can top it off - to the typical 1/2 way mark on the dipstick. Well that was probably at least 3 to 4 quarts too much since the engine sat for a long time before I drained the tank. I think I drained the engine one day and was also working on other things. Didn't get around to re-filling it until another day. So I believe that's how I forgot to drain the engine sump.

I wanted to mention the details behind my over-fill episode so people don't think that being slightly high on the dipstick is going to make your engine puke loads of oil like I experienced. Mine was a combination of way too much oil and stupidity. I'm lucky I didn't hydro-lock the engine and bend a connecting rod. Hydro-lock is when the engine tries to compress all that liquid, and can't, and expensive things happen. This is typically what happens when people make the bad decision to drive their vehicles through deep flood water and the engine dies when it sucks in a bunch of water through the air filter.