Cylinder deactivation can help improve an engine's fuel efficiency

by Jim KerrBackyard Mechanic . Apr 13 2018
General MotorsThe 2018 Cadillac CTS has engine cylinder deactivation technology.

General Motors

The 2018 Cadillac CTS has engine cylinder deactivation technology.

Question: I am considering buying a new Cadillac CTS, which has engine cylinder deactivation. Since I am not familiar with this type of engine, its benefits, functionality and reliability, can you offer your expert opinion on this type of engine. Would you purchase or do you own a vehicle with cylinder deactivation?

— Elmer

Answer: Cylinder deactivation is an engine control system that turns off the fuel and stops the intake and exhaust valves from opening on a cylinder to save fuel when power requirements from the engine are at a minimum. The first to implement cylinder deactiv-ation was Sturtevant, way back in 1905. Their 38/45 horsepower engine could have three cylinders stopped for fuel efficient cruising.

Cadillac implemented it back in 1981 with the V-8-6-4 engine, which as the name suggests could run on eight, six or four cylinders. While mechanically the system was sound, it lacked today’s modern electronic controls and got a bad reputation for its rough operation.

In the past decade, Honda and General Motors have been using cylinder deactivation on some of their vehicles to improve fuel economy and the computer controls operate seamlessly. Most drivers won’t even be aware when cylinders are deactivated. I have driven most of these vehicles and even when trying to detect it, find it almost impossible to sense.

In the Honda system, the computer uses Honda’s VTEC rocker arm system to prevent the valves from opening and turns off the fuel. In GM’s and the Cadillac system, the hydraulic lifter is deactivated to stop the valves from moving and the fuel is turned off. The Cadillac system currently runs in either eight or four cylinder mode, although GM recently announced the new Sierra Denali pickup will have a V-8 engine capable of running on any number of cylinders from one to eight.

When driving, GM’s engine will run on all eight cylinders at idle for smooth operation and when the throttle is over about 10 per cent open so power can be provided. During light throttle cruise, with an engine up to operating temperature, the computer will turn off four cylinders, but as soon as you step on the throttle even slightly or start to drive up even a slight hill, all eight cylinders fire up again.

If you drive fast, somewhere over about 105 km/h, depending on road and wind conditions, cylinder deactivation won’t engage because you need the engine power. Also, even under light cruise, the system will operate on all eight cylinders for about one minute out of every 10 minutes to keep all cylinders warm.

I have owned a GM truck for about 10 years with cylinder deactivation and it operates seamlessly and improves fuel economy, especially when cruising between 50 and 90 km/h. The only significant problems I have seen with the system are related to hydraulic lifters not operating correctly — this was almost always traced back to vehicles that had not been maintained with regular oil changes.