Yes I am looking at the Billet turbo from forefront. Not sure if I have an intercooler, what does it do?
Thanks, I will get compression test done. When I took off the turbo's front plate there was probably less than about 1/4 of a teaspoon of oil sitting there, in front of the impeller.
An intercooler (more correctly in this case called an "aftercooler" but we'll use the common name) tries to cool down the temperature of the compressed air coming out of the turbocharger. When you pressurise a gas, the gas heats up - so the air coming into the turbocharger might be at 30C, but it's going to be over 200C as it comes out. That's not because of the nearby hot exhaust - it's because of the pressure the gas is under.
This hot air can be cooled before entering the engine. Cooler air is more dense (hot air rises for a reason) so by cooling it after its been compressed, you're squeezing more air into the combustion chamber = more power. It's not a huge gain, but it's there and it helps lower combustion temps as well, which is important to engine longevity.
Intercoolers are obvious with the bonnet up. The outlet of the silver side of the turbocharger will have a large rubber hose which leads along either fairly directly to the intake manifold on the other side of the engine (meaning there's no intercooler installed) or it leads down to something that looks like a radiator without a cap. That's the intercooler. Some cars have top mount intercoolers (TMICs) - they do the same thing, but perhaps not quite as efficiently as a front mount intercooler (FMIC).
That oil in the front of the impeller is nothing to worry about. You'll discover a small (maybe 25mm diameter) hose plumbed into the air intake just in front of the turbocharger. The other end of this hose leads to the top of the engine at the rear (usually). It's called PCV - Positive Crankcase Ventilation. That's where your oil is coming from, and catch cans can remove MOST of that oil from the PCV line.
Why is the PCV directed there? Emission control laws. The gas that comes out is a mixture of pure exhaust gas and oil vapour. It's there because when the fuel in each combustion chamber ignites, most of the expanding gas inside the chamber pushes the piston down, but a little seeps past the piston rings and enters the crankcase. That's called blow-by, and it happens more at higher rpm and even more when the engine is labouring.
Because that's pure combustion gas, it's hot, and as a result heats the sump oil up a little - causing it to vaporise (in tiny amounts, don't worry). This is passed up and out and into the air intake where the exhaust and oil mix is introduced to the combustion chamber where the gas and oil are burned properly and sent out the exhaust. It does result in fewer emissions, partly because you're not spraying the oil everywhere, and also because the exhaust gas dampens the combustion process (which is further dampened by the EGR, read about that elsewhere). It enters before the turbocharger so that the turbo can help suck the fumes out, instead of pumping fresh air into the crankcase.
So the oil you're seeing is not a worry.
If you don't have an intercooler, consider one as insurance. Rebuilding a diesel engine is an expensive exercise. Even if you opt for an $80 intercooler from an XR6T Falcon, it'll still catch the bits of busted impeller that could do damage to your engine.
