CAR DOCTOR Q&A: Does Gasoline Direct Injection Cause Oil Dilution?

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Direct injection is essentially how every car  is delivering fuel now. Is there any correlation between direct injection and oil getting in the fuel? AAA Car Doctor John Paul gets to the bottom of it.

Q. I’ve been driving a turbocharged Hyundai Sonata for the past 4 years. During the past year I read about concerns of oil dilution from unburned fuel with direct injection engines. This past winter when performing my weekly oil check on both our cars, I gave the oil on the clean rag the sniff test. To my surprise, the sample from my wife’s car smelled like typical used motor oil, however my sample had the distinct smell of 2-cycle exhaust.

In addition to my car being the one with direct injection, I also have only a 10-minute commute to work. The best I could come up with is that an excessive amount of fuel was getting into the oil during warmup because of the rich mixture in the extreme cold.

2011 Hyundai Sonata

As soon as Spring had sprung, I decided to head off any problems and performed an oil and filter change even though there was only 2500 miles on that oil. Things seem ok so far with 1000 miles on the new oil. Do you or your colleagues have an opinion with respect to direct injection and engine longevity? I know some engines are also developing valve deposit problems. I also wonder if manufacturers have looked at the long term effect of direct injection in cold climates.

If gas is getting into the oil mainly during warm up each day, then 100,000 miles on a test track may yield different results from 180 cold starts over the span of a 6 month

A. The first place to start would be to consider having the oil analyzed. This test will give you an indication of how the oil is holding up and if there is excessive contaminants in the oil. Oil analysis kits can be purchased at local auto parts stores or online.

The concept of direct injection is not a new one, after all diesel engines are direct injection. Direct injection can be responsible for carbon build up in the engine but I haven’t heard much about oil dilution causing any long term issues with gasoline engines.

One thing to be aware of is not all synthetic oil is created equal. Some oil is actually made by fracking and is actually gas based and may just smell differently. Certainly your driving habits can contribute to oil dilution/contamination since the engine in your car barely warms up and is reason enough to change the engine’s oil a bit more frequently than someone who has a longer commute.

John Paul is public affairs manager for AAA Southern New England. A certified mechanic, Paul tests dozens of new cars each year and also hosts a radio show on AM 950 and 550.