Gasoline direct injection (GDI) is now standard on most new engines, including GM's 3.6 V6 family (LLT, LFX and LGX) and its current V8s. Automakers adopted it largely to meet tougher fuel-economy and emissions standards, and it delivers on efficiency. What few owners are told is that it also creates a durability problem that never existed with port injection: fuel getting into the engine oil.
That problem is called oil dilution, and it is behind a growing share of the bearing, lifter and camshaft failures showing up in modern engines.
What is oil dilution?
Oil dilution is raw gasoline mixing into the engine oil. Gasoline is a solvent. Once it is in the crankcase, it thins the oil and strips away its ability to protect the parts that depend on it, and the wear that follows can end in premature engine failure.
How fuel gets into the oil on a GDI engine
- Fuel is sprayed straight into the cylinder. A GDI engine injects fuel at very high pressure directly into the combustion chamber, instead of into the intake port where it mixes with air first.
- Cold cylinder walls get washed down. On cold starts and short trips, liquid fuel hits the cold cylinder walls, washes past the piston rings and drips down into the oil pan.
- The fuel never cooks off. Oil has to get fully hot and stay hot for a while to boil trapped fuel back out. A vehicle that rarely sees a long drive never gets there, so the gasoline keeps building up in the oil.
Why diluted oil leads to engine failure
- Loss of viscosity. Gasoline thins the oil and takes away the film thickness it needs to keep parts separated.
- Metal-to-metal contact. Thinned oil cannot hold a strong film under load, so high-friction parts like bearings, lifters and camshafts start to wear against each other.
- Additive depletion. Fuel breaks down and uses up the additives that protect against friction and oxidation, so the oil is spent long before the change interval says it is.
Why some GM engines are hit harder
Modern GM engines already ask a lot of their lubrication systems. V8s with Active Fuel Management or Dynamic Fuel Management, and turbocharged engines, run tight tolerances and see oil aeration under load. When fuel dilution weakens the oil on top of that, valve lifters and rod bearings face a much higher risk of oil starvation and mechanical failure.
What you can do about it
- Get the engine fully hot regularly. A good highway drive gives the oil time to reach temperature and boil off the fuel it has collected.
- Change oil on the severe-service schedule if the vehicle mostly makes short trips, idles a lot or tows.
- Have the oil analyzed. A used oil analysis reports fuel dilution directly and tells you whether your driving pattern is a problem.
- Keep the crankcase properly ventilated. Crankcase ventilation is the path fuel vapor and blow-by take out of the engine. The Tracy Lewis catch can system is a patented air/oil separating crankcase evacuation system designed to keep that path working and to stop oil and contaminants from being fed back into the intake.
Not sure what fits your vehicle? Browse Tracy Lewis catch cans by make, read the Oil Catch Can Guide, or call us at (941) 981-3930.
FAQ
What is oil dilution?
Oil dilution is raw gasoline mixing into the engine oil. Gasoline thins the oil and strips away its ability to protect bearings, lifters and camshafts.
Why do direct injection engines have more oil dilution?
A GDI engine sprays fuel at high pressure directly into the cylinder. On cold starts and short trips, liquid fuel washes down the cold cylinder walls, past the piston rings and into the oil pan.
How can I reduce fuel dilution in my oil?
Get the engine fully hot regularly so the fuel boils off, change oil on the severe-service schedule if you mostly make short trips, have the oil analyzed, and keep the crankcase properly ventilated.