Tech Article: Making Turbos Last Longer
by Ben Pila
A turbocharged engine makes more power than the same engine without one due to a small part called a turbocharger. With this part, it takes the spent exhaust gasses that normally leave the engine out the tailpipe and uses those gasses to drive a turbine wheel. The exhaust turbine wheel is connected to a shaft that has another wheel/impeller on the other end called a compressor wheel. As the turbine wheel spins up, the compressor wheel (which is in the intake path,) actually pulls in more air and then pushes it into the cylinders. With the extra air into the engine, the computer adds more fuel netting more power.
One situation that happens as a result of the extra horsepower gained from a turbo is a lot of heat in the center housing section of the turbo. This is a direct result of hot exhaust gasses passing through the turbine side of the turbo. As much as 1500 degrees F. can play havoc on the cast iron housings. More importantly is that the oil flowing through the center housing to keep the bearings lubricated can break down at temperatures of 350-400 degrees F. If the engine was shut off while the turbo's temperature was high, the oil in the center housing might coke or carbon up. If this condition continued over a period of time, the turbo bearings might be deprived of the oil it needs as the oil passages get restricted resulting in a bad turbo.
What is a turbo timer and why were they needed? A turbo timer is used to keep the engine running after you shut off the ignition switch. With a turbo timer, you lock up the car, then the engine would continue to run a few minutes and then shut off automatically. The purpose of keeping the engine idling a few minutes before shutting it off was to allow the hot, center section of the turbo to cool and minimize the chance of carbon deposits building up in the bearings and center section of the turbo.
Turbo timers (which are aftermarket add-ons,) were developed when turbos were first used on cars that only had oil flowing to the center sections. Zs from 1981.5-1989 had turbos with only oil flowing in them. Since the 1990 Z came out, it's turbochargers have engine coolant flowing into cooling passages built into the center section. This design keeps the center section's temperatures more stable than the earlier non-water cooled turbos. As a result there isn't as much need for a turbo timer on these models. In a few circumstances such as using your car on a track day or a drag racing event, it might be good to allow the turbo to cool by idling the engine a few minutes. Also just driving around a few minutes at low or no boost would be sufficient to cool the center housing down.
Other things to consider when using turbo timers or idling the engine too long is the possibility of more oil consumption, carbon build-up behind the heat shield internally in the turbo housing, and smoke out the tailpipe. The oil seals on many modern turbochargers are a dynamic type that uses exhaust pressure in the turbine housing to push the oil seal tight. The turbo's shaft rotation keeps oil flowing off the shaft and away from the seals. Yet another problem is that when the engine is idling and boost is non-existent, oil can acutally flow past the exhaust turbine seal and get into the exhaust where it gets burned which you could see as smoke out the tailpipe. This condition is more likely to occur when the engine is cold. It is best to avoid long idling when the engine is cold. It is also good not to idle any longer than necessary to cool the center section. Again a few minutes of easy driving would normally be enough to cool a water cooled turbo.
Another important thing to do to prolong the life of the turbo is to keep the engine oil clean. Dirty engine oil contributes to carbon build-up in the turbo and can prematurely wear out the engine bearings and/or restrict the oil supply and return passages. Using a high quality synthetic oil can minimize carbon build-up as synthetic oils have a much higher heat resistance.
Take care of your turbo and you"ll enjoy the "boost" for many miles!