Cylinder Shutoff Was A Trap - Auto Engineer Explains Cylinder Deactivation and Why It Failed

Summary

The video explains why automakers adopted cylinder deactivation and why these systems can become costly reliability risks.

How it works

At light engine loads, a V8 or V6 can run on fewer cylinders to reduce fuel use. But simply cutting fuel and spark is not enough: inactive cylinders could pump cool air through the exhaust and harm emissions performance. The system must also prevent their valves from opening.

System designs

• GM Displacement on Demand/Active Fuel Management and Chrysler Multi-Displacement System use specialized hydraulic lifters in pushrod engines to disconnect valve motion.
• Honda’s system uses a VTEC-style rocker mechanism that switches to a zero-lift cam profile.

Fuel-economy tradeoff

The speaker estimates fuel savings at roughly 5–10%, depending on the engine—not anything close to cutting fuel use in half.

Common concerns

The specialized lifters are heavier and more complex than standard lifters. According to the speaker, their added mass and contact loads can contribute to wear or failure, including roller damage and lifters that stop switching correctly. Camshaft damage can make repairs substantially more expensive.

The speaker recalls fewer failures with Honda’s system, while noting that it may contribute to additional engine wear.

Repairs and prevention

Software can disable cylinder deactivation, but this leaves the heavier lifters in place and does not eliminate the mechanical concern. A more complete conversion replaces the specialized parts with standard lifters and related components. If the camshaft has been damaged, deeper engine disassembly may be necessary. The speaker says these repairs can cost thousands of dollars.

Buying advice

The speaker would consider buying a vehicle with cylinder deactivation, but would check its service history, listen for abnormal engine noise—especially at startup—and account for possible repair costs. For a vehicle they planned to keep, they would consider a full conversion rather than relying only on software deactivation.

Why automakers used it

Cylinder deactivation was intended to improve fuel economy while allowing automakers to retain large V8s or V6s and meet emissions and economy goals. The speaker describes it as a reasonable engineering attempt, but says it was difficult to make fully reliable. Turbocharging and smaller engines are mentioned as another way to balance fuel economy with available power.

Main speaker and source

The video’s host speaks as an automotive engineer and draws on experience working with engineers at suppliers involved in GM and Chrysler systems.