blowby????

To push oil from the turbo to the aftercooler at the hump hose clamps leaves you with only one thing to look at..........the turbo. The turbo has its stand alone oil source from the engine. There is no other place the oil can come from on the air inlet side between the turbocharger and the aftercooler, but the turbocharger. Unless someone is pouring oil in you air inlet piping from the air filter.

Now the thing that bothers me about this is from what you've posted you have tried more than one turbo already. The likely hood of having multiple turbos with bad seals is extremely unlikely. What type of air filter system do you have on this truck? What type of exhaust system do you have on this truck? The reason I'm asking is, I'm wondering about air inlet restriction problems and exhaust outlet restriction problems. To have a major restriction in either system creates problem with the turbo's balance and whether it is riding hard against the thrust bearing internally. But thrust bearing problems don't usually cause an issue with the oil shaft seal until the turbo is ready to fail and the wheels are hitting the housings.

When you take the compressor cover off, look for the oil to becoming from the outer edge of the compressor wheel at the bearing housing backing plate. This should be easy to see. If you can't see anything then wipe the backing plate with a clean white paper towel for evidence of oil. If you still don't see anything then the turbo id fine. But then we need to find the source.


The 6NZ draws the air intake for the air compressor from the Intake Manifold in the cylinder head of the engine. This is well after the turbocharger, aftercooler and hump hoses and wouldn't be the source of the oil at the hose clamps at the turbocharger. Has somebody changed the air supply source to the air compressor? If somebody modified the air inlet to the air compressor to draw clean atmospheric air from the air filter assembly or air filter piping then you can suck oil from the air compressor into the air inlet of the turbocharger. If they this and did not install a inlet check valve on the air compressor, you can suck oil into the air inlet of the turbocharger. This could then been drawn into the turbo and pushed out the other side to the hoses to leak. But again you would see evidence of oil contamination inside of the compressor cover of the turbo.

The fuel mileage drop and poor performance is more than likely caused by the LOW NOX file in the ECM. Usually the LOW NOX file causes a 10% loss in fuel mileage at the same power level. With you upgrading to a 550 with a LOW NOX file versus the 475 file, it will be a higher fuel mileage loss in my opinion.