Insights for Diesel Owners: the Pros and Cons of Turbochargers

Turbo cutaway

Last week we looked at a triple turbo diesel setup that was quite intriguing and incredibly powerful. In that article we looked at how turbochargers can improve horsepower and torque. But we never examined the downside of turbos. Are turbochargers always beneficial? Is there a downside to turbos that people can neglect to consider? 

Turbos have generally been add-ons that improve engine efficiency and performance. In recent years more and more vehicles have been fitted with turbochargers from the getgo.

The way a turbo works is like this: hot exhaust gasses spin the turbine that is connected to another turbine which sucks air in and compresses it into the engine. It is this compression that provides the engine with extra power. The more air you can get into the engine, the more fuel can be added for more power.

We're fairly well acquainted with the benefits of turbochargers. Extra power is primary. Unlike superchargers, there is no engine drain because the power comes from hot, expanding gases coming out of the engine already. In addition, turbos aren't affected by the thinner atmosphere of higher altitudes. Furthermore, turbos provide better fuel economy, so they are a win-win on several fronts.

What's the downside then?

The first is heat. Turbos are powered by hot exhaust gases and they get hot, hot hot. How hot? Hotter than molten lava! When pushed to its limits for a continuous amount of time the turbo can start glowing red. For this reason racers have vents to get air circulation flowing through the engine bay. 

The second is friction and heat in the turbine itself. Think about this for a second. Your engine revs at 2,000 rpm when cruising. Your turbo's turbine can reach speeds of more than 280,000 rpm. When I wrote, "Think about this for a second," it was to make you think about this: in one second that turbine will spin as many as 4,666 times. Try wrapping your head around that... more than 4500 times a second. That's a lot of friction there if the lubrication is insufficient.

This turbocharger bearing system is lubricated by the oil from the engine which is fed under pressure into the bearing housing. The oil is both lubricant and coolant. This is one more reason that the engine oil you select meets specifications.

Another disadvantage with turbochargers that doesn't get talked about much is "turbo lag." At times, when conditions are right (or wrong), there will be a delay between the moment you stomp on the pedal and the moment you actually feel power. This is turbo lag. 

At low speeds there aren't a lot of exhaust gases passing through the turbo, "so when you demand power from the engine, the turbocharger turbine needs time to start spinning at an optimal speed. The effects of this can be reduced by downshifting to a lower gear." Astute drivers will still notice the split delay at times.

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Because of their benefits, turbochargers have almost universally become stock equipment on diesel pickups and will be around for years to come. It's useful, however, to be aware of their shortcomings.

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Sources 

What Is a Turbocharger and How Does It Work

Eight Things About Turbochargers You (Probably) Never Knew