Lubricating the shaft inside the turbo is not too difficult and most turbo manufactures provide adequate oil feeds to the shaft's bearing housing. However, the extremely high temperatures that the turbine creates will cause the oil in the bearing housing to disintegrate and loose its viscosity and lubricating qualities and will cause coking in the turbo bearing housing. Coking will impede the flow of oil to the bearing and will exacerbate the problem. Four things contribute to coking:
- High temperatures in the turbo's bearing housing
- Using engine oil that is not capable of operating in high temperatures
- Using engine oil that has a wide multi-viscosity range — the additives used to achieve multi-viscosity are the material that causes coking
- Not changing the engine oil frequently enough
There are two simple solutions to this problem:
- Change the engine oil more frequently
- Get a turbo with a water jacket around the bearing housing. It might be a good idea to look out for a turbo with a water jacket around the bearing housing when selecting a turbo
The best engine oil you can use in your turbo engine is a synthetic, straight viscosity oil that is suitable for the temperature range of both the climate in the area that you live, and the engine.
The important thing is to change the engine oil and oil filter regularly. Even if the turbo has a water jacket around the bearing housing, you should still change the engine oil more frequently than on naturally aspirated engines, and you need to do this diligently! Changing the engine oil every 2,000 miles should do the trick.
You also need to ensure that the oil pressure to the turbo does not exceed 70 psi or else that oil will push past the oil seals in the turbo and cause frequent, if not continuous, smoking. If your oil pump produces more oil pressure than the turbo’s seals can handle, you should install a restrictor in the oil feed line, or a bypass system to reduce the oil pressure to the turbo. A bypass system is more reliable but in both cases you must ensure that the oil pressure to the turbo is adequate at idle and at full operation.
The oil seals in the turbo do not operate properly if they are bathed in oil, therefore, you should ensure that the oil return line to your oil sump is big enough to allow for proper drainage. The oil return line should have an inner diameter of at least a ½ inch. The oil drain hole in the turbo should also be aligned as near vertically downward as possible.
Best practice to ensure that your turbo lasts is to cruise at low RPM where no boost pressure is created for the last 15 minutes of your journey to let the turbo cool down properly. Some people suggest that you let the engine idle for 30 seconds before turning off the engine, or install a turbo timer to automate the task, but the oil pressure at idle speeds is too low to provide sufficient lubrication. You need at least 1,500 RPM for enough oil pressure to ensure that the bearings and shaft receives sufficient lubrication while the turbo cools down. It is for this reason that we do not recommend installing a turbo timer. You should also change the engine oil every 2,000 miles, and use a high-quality, synthetic, straight viscosity oil. These three simple things will ensure that you prolong the life of your turbo and that you never need worry about coked up turbo bearing failure again.