Can the CT6 use 5W40 engine oil?

[JaceDella]

The CT6 can use 5W40 engine oil. Engine oil, also known as engine lubricant, serves to lubricate and reduce friction, assist in cooling, seal against leaks, prevent rust and corrosion, and provide cushioning for the engine. Taking the 2021 CT6 as an example, its body dimensions are: length 5223 mm, width 1879 mm, height 1492 mm, with a wheelbase of 3109 mm and a fuel tank capacity of 72 liters. The 2021 CT6 is equipped with a 2.0T inline 4-cylinder turbocharged engine, producing a maximum horsepower of 237 HP and a maximum power output of 174 kW at 5000 RPM, paired with a 10-speed automatic transmission.

[StPeyton]

I've gone through the maintenance manual of my CT6 several times, and GM specifically emphasizes using engine oil that meets the Dexos1 standard. The 5W40 viscosity is a bit too thick for the newer engines, especially those with cylinder deactivation technology. A while back, a technician at the dealership mentioned they've seen quite a few owners using the wrong oil grade, which not only increases fuel consumption but also triggers fault codes. For the 2.0T engine, it's best to stick with the manufacturer-recommended 5W30, as the variable valve timing system is highly sensitive to oil fluidity. Experienced drivers advise against switching to higher viscosity oil too soon in a new car; wait until you've driven over 80,000 kilometers before considering adjusting the oil grade. I just saw a post on an auto repair forum where a fellow car owner reported that using high-viscosity oil improperly caused the cylinder head gasket to leak, which is really not worth it.

[MacAlan]

Having worked in the auto repair shop for twenty years, I've handled at least a hundred CT6s. 5W40 isn't completely unusable, but it depends on the engine model! The LTG 2.0T before 2017 could manage, but engines with Active Fuel Management System after 2018 will definitely act up. Just last week, I dealt with a case where the owner switched to 5W40 to save money, and the start-stop system immediately went on strike. The engine light came on the dashboard, and the fault code showed abnormal oil pressure. Switching back to the factory-recommended 5W30 cleared the code in half an hour. American cars are quite delicate now, especially systems controlled by solenoid valves—if the oil film is too thick, the response lags. For older cars with over 150,000 kilometers, you might consider using 5W40 to alleviate oil consumption issues.

[MacCharlotte]

Compared to 5W30, 5W40 has significantly higher viscosity at high temperatures. The precision of the CT6 can be understood by looking at its turbocharger clearance – an overly thick oil film affects cooling efficiency. I conducted an experiment using oil test strips: under the same temperature conditions, the diffusion ring of 5W40 was noticeably smaller. The manufacturer's recommendation of 5W30 isn't without reason; it meets the 100°C kinematic viscosity standard of 9.8cst while offering better low-temperature pumpability. Last time I checked the workshop computer records at the dealership, 2.0T engines using 40-weight oil showed 0.3L/h higher idle fuel consumption during cold starts. In the long run, it actually costs more money. Unless you frequently track your car and push oil temperatures to 150°C, there's really no need for higher viscosity oil in daily commuting.