Folks, reading through the last few pages of posts here, let me chime in with my personal experience on not one, but two Garrett G35-900 turbos i have been through. The first failed at ~2030 km. the second failed at ~2300 km.
The nature of failure was very gradual, with a faint, low frequency "Police siren" or "wooooo" noise accompanying spool, that gradually got louder to the point where the compressor inducer was seen to make contact with the compressor housing, and the shaft was bent.
Oil feed lines on both were brand new. No oiling issues, as all Oil parameters are monitored. No coolant supply problems either.
Tune was carried out by the most respected JDM Builder and tuner here in Dubai, and happens to receive, build and tune vehicles from all over the middle east and north Africa.
The first turbo was sent to Garrett for inspection, and they responded with the following:
880695-5001S
Analysis Findings : Rotor damage - Overspeed -
Technician Conclusion: Turbocharger returned with rubbing wheels vs. contours. Damage of compressor piston rings and overheated of ball bearing as a consequence of Turbo overspeed. During overspeeding cycles, the excessive growth of the compressor wheel may cause a permanent deformation (growth) of the central bore of the wheel, which forms into a barrel shape and is characteristic of a wheel which has been taken beyond its normal operational speed limit. Recommendations: The reason for turbocharger overspeeding needs to be investigated on the vehicle. Possible contributing factors: performance tuning, fuelling problems, poor combustion causing high level of deposits in VNT (vanes blocked). Actuator not controlled correctly: ECU problems, command from ECU not reaching actuator, wiring/connection faults, actuator hose leakage, PWM valve faulty, hose blow-off etc may be contributing factors. Blocked/restricted air filter or hoses.
The turbos failed due to overspeed, and were not happy pushing 2.5 bar of boost for extended durations. Both failures were consistent in nature with respect to how they occurred as well as the time period/mileage as the tunes and driving style were more or less identical in nature.
I did not bother sending in the second unit for a claim.
I would recommend Either Garrett GTX Gen 2 as those are extremely robust, (I have run a GTX3071r , and GTX3076r in the past) or Precision CEA to avoid going through similar hassles.
I am now swapping in a Precision 6466 CEA Gen 2.
Hope this helps some of you decide. If you do purchase a G Series Garrett turbo, don't make the mistake i made; do buy a turbo speed sensor, and follow it religiously as part of the tuning process.
