Turbocharger question. - Page 2 - PeachParts Mercedes-Benz Forum

tjts1 · #16 05-12-2018, 06:29 AM

Here's a demonstration on the bench why a turbo can't leak out the compressor housing because of a bad seal.
https://youtu.be/5TYZChIdy14

Diseasel300 · #17 05-12-2018, 10:17 AM

A turbo can and will leak into the compressor housing when the seal fails. The video you linked has the shaft stationary, add in the rotating component, crankcase pressure as he mentioned, hot thin oil, and worn seals and it will indeed leak oil at no or low boost levels, it isn't much, but it's still a leak.

Oil outside the compressor will likely not originate from the turbo unless there's some sort of external gasket leaking or an O-ring on the compressor outlet letting oil drip down the housing. The compressor shaft seal leak will usually just get sucked/blown into the engine and burned.

tjts1 · #18 05-12-2018, 10:32 AM

Quote:

Originally Posted by Diseasel300

A turbo can and will leak into the compressor housing when the seal fails.

No, this is incorrect. The front and rear shaft seals are NOT oil seals. Whether you have the seal in place or not makes no difference. Any oil will can not be caused by those seals.

ROLLGUY · #19 05-12-2018, 10:39 AM

Quote:

Originally Posted by Diseasel300

A turbo can and will leak into the compressor housing when the seal fails. The video you linked has the shaft stationary, add in the rotating component, crankcase pressure as he mentioned, hot thin oil, and worn seals and it will indeed leak oil at no or low boost levels, it isn't much, but it's still a leak.

Oil outside the compressor will likely not originate from the turbo unless there's some sort of external gasket leaking or an O-ring on the compressor outlet letting oil drip down the housing. The compressor shaft seal leak will usually just get sucked/blown into the engine and burned.

I believe this to be true, and have experienced a leaky turbo seal firsthand. My former Mitsubishi truck with a 2.3 Turbodiesel had a bad seal in the turbo. It got worse and worse on a trip a few years ago. Driving at highway speeds, there was very little smoke (barely noticeable). When I would come to a stop for a traffic light idling, the blue smoke would start small, and crescendo into a James Bond style smoke screen! After this happened several times, I decided to shut down the engine at the stoplights. After I got home from the trip, I replaced the turbo with one I had from my spare engine. Problem solved, no smoke whatsoever.

Diseasel300 · #20 05-12-2018, 10:44 AM

Quote:

Originally Posted by tjts1

No, this is incorrect. The front and rear shaft seals are NOT oil seals. Whether you have the seal in place or not makes no difference. Any oil will can not be caused by those seals.

Call it what you want, the point of the seal is to keep the compressed air in the compressor housing and the oil in the cartridge. If it had no point, it wouldn't be there in the first place.

Leaking turbos are a very common thing, the carbon sealed variety are known for causing diesel engine runaways if the turbo seal fails.

Turbos can and do leak. Add wear and rotating components and oil will leak out of just about anything.

tjts1 · #21 05-12-2018, 11:15 AM

Quote:

Originally Posted by Diseasel300

Call it what you want, the point of the seal is to keep the compressed air in the compressor housing and the oil in the cartridge. If it had no point, it wouldn't be there in the first place.

Leaking turbos are a very common thing, the carbon sealed variety are known for causing diesel engine runaways if the turbo seal fails.

Turbos can and do leak. Add wear and rotating components and oil will leak out of just about anything.

Its only real job is to prevent the shaft from sliding back and forth. It also helps keep boost pressure out of the oil return line to some extent but it's not a perfect seal. There is no oil seal in a T3 turbo. The vast majority of oil leaks out of a T3 core are cause by a blockage in the oil return. Either the diameter of the return is too small or the oil level is too high. A real oil seal would have to be tight around the shaft which doesn't work at 100k+ RPM. The T3 core is designed with large passages around the ends of the shaft that allow the oil to be flung out away from the shaft and then drain down into the return. The only way to get this turbo to leak out oil is to block the return. You can get one of these turbos brand new place it on it's end and oil will leak out of whatever end is pointed downward. Some turbos like the GT series can be mounted on an engine at 30-45degrees (see OM606). Not the T3.

Diseasel300 · #22 05-12-2018, 12:04 PM

The seal design used on the Mercedes is a "dynamic" seal. It relies on the rotation of the shaft and the viscosity of the oil to work. When the shaft is stationary, it will leak, you are correct. But when the turbo is in operation it will not. When the ring wears or the mating surface in the thrust bearing wears, oil will weep past and be hurled away by the compressor wheel spinning at incredible RPM. It DOES happen. I'm sure more than just a couple people on this forum have dealt with it personally.

ROLLGUY · #23 05-12-2018, 12:29 PM

Quote:

Originally Posted by ROLLGUY

I believe this to be true, and have experienced a leaky turbo seal firsthand. My former Mitsubishi truck with a 2.3 Turbodiesel had a bad seal in the turbo. It got worse and worse on a trip a few years ago. Driving at highway speeds, there was very little smoke (barely noticeable). When I would come to a stop for a traffic light idling, the blue smoke would start small, and crescendo into a James Bond style smoke screen! After this happened several times, I decided to shut down the engine at the stoplights. After I got home from the trip, I replaced the turbo with one I had from my spare engine. Problem solved, no smoke whatsoever.

Let me add, that the failed turbo bearings (bushings) were so worn out that the compressor and turbine rubbed their respective housings. Yes this is the worst one I have seen and heard about, and is no wonder so much oil got into the compressor section.