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Ed,
Hope all's well!
Most turbochargers can function with very low oil pressures. The GARRETT minimum pressure requirements are between 5-7 psi at idle. The turbocharger can have too much oil delivery/pressures which can allow for volume to build within the bearing housing and cause bypassing/blowby. Since your oil pressures have prob. not increased, you might check potential culprits that may restrict oil from returning to the crankcase such as: Positive crankcase pressures or improper ventilation, restriction within the return line, high oil levels, etc. Even with a new turbocharger, oil levels or pressures that may build within the turbocharger bearing housing will allow for bypassing past this assembly's piston ring oil seals.
The other potential culprit to bypassing is that the turbocharger oil seals are worn.
The oil seals on both compressor and turbine are piston ring assemblies and are identical in design to the engine cylinder piston ring assemblies. These rings are in service within a bore and has an installed gap which is allowing for thermal expansion of the ring.
As time is put on the turbocharger, the piston ring oil seals may wear which causes its respective gap to increase and will always allow for additional oil bypassing under normal oil delivery conditions. The gap within the piston rings should be under .013" at the turbine and .008" at the compressor and may need a simple replacement if over this specification. For insurance against potential bypassing, a staggered gap ring could also be employed to address typical problems (oil bypassing) at the turbine.
Larger turbochargers can have additional bypassing issues because of their slower rotating shaft speeds at idle and lower oil consumption but this is something that you should not need to contend with.
Best regards and good luck,
GaryK at SWEDISH DYNAMICS,INC.
posted by 152.163.100...
http://swedishdynamics.saabnet.com
, Fri, 8 Apr 2005 15:34:12, Sat, 9 Apr 2005 06:56:55, Sat, 9 Apr 2005 07:20:26
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