Have your 993TT turbochargers failed? - Rennlist Discussion Forums



Have your 993TT turbochargers failed?

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Old 09-10-2005, 01:08 AM   #1
Kevin
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Default Have your 993TT turbochargers failed?

Everyday I open my emails and receive question asking why there is oil dripping from the turbochargers. The second question is, my car is smoking, how can I fix it. It would be extremely foolish for me to say that the turbochargers have failed and that they need to be rebuilt or replaced. The truth is, it takes a few questions in order to try to trouble-shoot the situation.

1) Without a doubt, if your cars starts smoking and puddles appear on your garage floor after an oil/filter change, the likely cause is the installation of a MAHLE Original Equipment Manufacture oil filter on the engine.. The part number is OC 213. AirKuhl has a great picture of his car parked in his garage with two puddles on both sides of the engine. He might post them. The other fault is that the oil level is/was hard to see during the fill up and the oil level is now to high. The oil has gotten hot and expanded. There is too much oil in the sump tank and engine case, I make the recommendation to run below the 1/2 way mark on the dip stick.

Many have asked what the actual reason for the leakage or why the car is smoking. If someone installs a Mahle filter, inside of the filter there is a bypass spring and diaphram. This diaphram/valve fails when the engine is shut off (this is a faulty filter design, it is/was corrected by Porsche, please buy a new filter from your Porsche dealer). [I must state that Mahle filters are very good, and I run them on all my other Porsches, but not on the 993TT] As the engine/oil cools, oil seeps past the spring loaded valve.. Oil is drained from the oil tank which is located in the right quarter panel. Through gravity, the oil makes its way from a higher tank level, through the oil filter (the one on the engine), then into the engine case.. As this oil level rises, it will backup through the turbo scavenge lines and raise the level inside of the turbocharger. The sealing rings in the turbocharger have gaps.. Oil freely passes these gaps and will spill into the turbine housing, and also make it's way past the heat shield and drip down the bearing housing to the floor.

One typically has a few hundred miles to cure this problem before carbon builds up in the seal area and heat shield are. Rapid wear occurs to the sealing ring, from carbon cutting like diamonds to sealing surfaces. Basically your non-failed turbochargers will turn into wear failed turbo's in need of repair.

2) My car has Porsche filters and the oil level is closer to the 1st mark vs the upper mark. I would recommend that you change the factory oil filter on the engine, because it could be damaged from the installation. You or your mechanic could have crushed the flimsy filter when installing, hey it has happened to me..

The next instructions would be to remove the plastic inlet pipes that are hose clamped to the inlet side of the compressor, or aluminum housing. This is not the rubber hoses that run to the intercooler. If you have oil puddling in the plastic pipe or dripping out of the compressor housing. You have a high likelyhood of failure caused by wear to the sealing rings on the turbine side (hot side). Another dead giveaway is the actual color of the aluminum compressor wheel. If it looks like burnt chocolate, oil has been passed through the seals and now is pressurized and pumped into the intercooler. In this cycle, if the throttle is shut, the oil now is recirculated with boost pressure through the bypass valve. The air then enters the turbocharger, the compressor wheel now gets slimmed with oil..

This is a warning, your turbocharged engine, needs good fuel, and high octane to run at maximum levels. If oil is introduced and is force fed into your engine as a mist, the actual octane rating of your fuel is lowered. Detonation occurs more easily. The knock sensors pull timing and boost as a result. Carbon builds up on valves and valve stems.. And on piston tops.. Which increases the compression ratio of your engine, thus causing detonation...

2a) As our engines age and get miles on them, leakdown numbers become more and more important. Combustion gases that would normally pass through the exhaust valves are now passing piston rings. This will pressurize the engine case and make it difficult for the oil that passes through the turbochargers to be scavanged by the sump pump. Oil is then blown up into the sump tank vent lines. This then makes it way into the engine combustion process. Many tuners will often plug off the vents on the turbo sump tanks to prevent this from happening.

2b) On some engines, with all things checked and re-checked. Installing 996TT anti-check valves that screw into the top of the turbocharger bearing housings, along with the installation of the 996TT style, scavenge lines that run from the turbo sump tanks to the scavenge pump. These lines have a inverted "P" trap to prevent the migration of oil. It is my opinion that both systems have to be used, check valves and new sump lines.

One more important note: When installing new turbochargers make sure that you have the shop install Porsche oil filters, you may even have to purchase them yourself. It's sad, to see things repeat themselves due to a $15 filter..
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Old 09-10-2005, 04:19 AM   #2
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Thank You Kevin you have answered questions I had regarding the Mahle oil filters and the problems I've read about them. Doug
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Old 09-10-2005, 05:28 AM   #3
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I am sure this is one of the most often asked questions to you and not many mechanics out there will know the right answer when asked. Excellent contribution, thanks.
I hope a moderator (do we have one?) or John D. puts it as a sticky, I am not sure this board is often monitored, since we are so trouble free .
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Old 09-10-2005, 06:16 AM   #4
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Quote:
Originally Posted by Jean
I am sure this is one of the most often asked questions to you and not many mechanics out there will know the right answer when asked. Excellent contribution, thanks.
I hope a moderator (do we have one?) or John D. puts it as a sticky, I am not sure this board is often monitored, since we are so trouble free .
I concur, this would make an excellent sticky.
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Old 09-10-2005, 10:29 AM   #5
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I agree as well. Sticky this thread, mod!!!!
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Old 09-10-2005, 11:36 AM   #6
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Thank you for the clear, understandable and thorough description of the issue.
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Old 09-12-2005, 02:07 AM   #7
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sticky it
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Old 09-12-2005, 03:41 PM   #8
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Thanks Kevin! You are a thoughtful kinda guy.

Bill
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Old 09-13-2005, 03:31 PM   #9
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*Bump*

I still think this should be a sticky
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Old 10-15-2005, 02:16 PM   #10
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I had this problem only after my car sat for a month (with only 300 miles on it after u rebuilt my turbos) while waiting for Gunthers program, I've since gotten an interim program as I continue to wait for Gunthers program and after driving the car regularly again have no smoking or leaking. Stephen from IA's (where the car was done) advice was an oil and filter change. I dont know what kind of filter they put on the car after the turbos were redone, but i will now call and ask them. I experienced this horendous smoking like i said only one time, after it sat. So now i understand that was not very good for my new prized turbos at all?? I dont want these things to fail, they were just done! I will make sure to go get the oil changed and order a new filter from Porsche (not mahle) and hopefully these turbos will make it. Thanks
-Justin
1996 993tt, IA stage 3 + sum
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Old 10-15-2005, 02:27 PM   #11
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whoops, ok kevin ur post says if the puddles and smoking occur after an oil filter change, my leaking was after a turbo rebuild, oil filter change and 30k service, AND only after sitting for sometime. I get no leaks or smoke if i drive it at least once a week. should i be worried?
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Old 10-15-2005, 02:29 PM   #12
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It might not be the turbochargers, when flat six engines sit for any period of time oil can/will pass the piston rings. This will collect in the cylinder heads and smoke on start up. Being that you also have new turbochargers, they need to get some miles on them. I'd also check the engine oil level, when the car is up to temp. The oil level should be at the 1/3-1/2 level on the stick.. Again make sure that you have a Porsche filter.
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Old 10-26-2005, 08:48 AM   #13
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Kevin - You mention that the Mahle filter is good for all cars except a 993TT. I have a 930 that has a Mahle filter. Any concerns there?
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Old 10-26-2005, 02:19 PM   #14
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Mahle filters are very good, on a 965 or on your 930, that is the filter of choice
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Old 01-13-2006, 04:20 AM   #15
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Kevin,
I recently installed the rebuilt turbos and noticed that they were leaking oil still..
during removal, the tubos were leaking oil not just from the impeller, but also the exhaust side.
There was evidence of burnt oil all around the turbo housing, where the aluminum and cast iron housing mates.
Upon returning the turbos to the shop, the tech said that the turbos were completely fine.. with no evidence of damage, and everything was still within spec, he did mention that the shaft had gone a little blue.. on the impeller side.. as if there was a mild oil starvation.

his opinion is that the oil return must be faulty, causing the pressure in the turbo resevoir to backup and cause oil to seep out from the housing.. previously this was never a problem.. only the seal.. as pe your inspection guidelines..

have u experienced this problem before? it is most baffling.. and most annoying.(read: install and reinstall is a PITA)

would be most grateful if you could offer an explanation or even a diagnostic criteria to check on the oil plumbing...

TIA.
Chunn
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