For the longest time, it was said that all LNF engines were only rated for 5w-30 oil. Everyone, from me on up, said do not use any 40 weight oil in a GM LNF engine.

Apparently, all of us were asleep at the wheel. I discovered recently the Opel GT version of the Kappa manual, and sure enough, Opel approved our engine for use with 0W-40 and 5W-40 oil (page 171 in the manual, by the way). It just has to be rated for GM-LL-A-025 quality oil. Today, that standard has been absorbed into the GM dexos2 standard.

For those not aware, the Kappa platform LNF cars (Opel GT, Saturn Sky Red Line, and Pontiac Solstice GXP) are identical cars when it comes to mechanics. Everything under the hood is identical.

So, how did this happen? Why were we told not to use 5W-40 oil? And why would you want to?

The devil, as it usually does, lies in the details. And this is far from the first time this has happened.

The US and Europe have different environmental standard for fleet averages. In English, the US and EU require different things from auto makers.

In the United States, the EPA judges cars based on the worst-case oil scenario. Meaning if your car gets higher MPG with a thinner oil, that thinner oil has to be the maximum recommended. If you recommend a thicker oil, as the manufacturer, you may have to reduce the MPG estimate.

For real environmentalists, such as myself, this is counter-intuitive. A thicker oil can mean a longer engine life, especially when you decide which oil to use long after the warranty has lapsed.

If the engine fails, the car is usually junked. This is a far greater harm to the environment, because modern cars are many-times more efficient when it comes to air pollution. They’re more efficient than leaf blowers, lawn mowers, and many other things that people run constantly in the millions of units per day.

As such, when an engine fails, it’s bad for the environment. So why force a thinner oil?

The EU understands this logic, and so they go with the best MPG estimate of all the recommended oil weights. Hence, in Europe, you might start your car with a 0W-20 oil, and as the engine ages (and seals wear/leak), you might step up to a 0W-30, and eventually, a 0W-40 oil.

There are performance benefits too. If you tune your engine beyond specification, or push it to the limit on a track day, a thicker oil can help keep vital components lubricated.

I mentioned this was far from the first time. Indeed, it has been known by Corvette owners for years that the Corvette team recommends 15W-50 oil for competitive driving and track days… they just have had to bite their tongue until it bleeds, when an American asks that question. The only place they have been able to note that reliably, is in the Chevy UK manual.

But as I mentioned, even I wasn’t aware of the 5W-40 rating on LNF engines until this week…

Auto makers should push back against this EPA policy. It leaves them in a moral hazard, where they are urging customers to use oils that might get them through the warranty period, but may in fact be harmful to use late in a car’s life. A car with over 150,000 miles that requires 5W-20 oil, could very easily leak out as seals wear, and then you have engine failure.

The counter argument is that people should just replace engine seals, but this costs several hundreds, if not thousands in some cases. People aren’t going to do that because it puts cars beyond economic repair in many cases. Had they known a thicker oil would stop those leaks, they’d be likely to use it. But they can’t – because the car’s manual stresses to not use thicker oil than recommended.

My car is still under an extended warranty. Which leaves me in a pickle. If I go by Opel’s guidelines, and my engine fails, the warranty provider might test the oil – and refuse to honor my warranty. Unlikely? Sure, but not worth the risk.

So, my LNF car will march on with 5W-30 oil… until the day that the warranty is up.

That said, if you have an older Saturn Sky Red Line, or Pontiac Solstice GXP (or heck, Cobalt SS or HHR SS), and it’s high mileage, you might want to consider a dexos2 5W-40 or 0W-40 oil.

There aren’t any 40 weight oils rated for dexos1 today, because dexos2 is the European-and-diesel blend, and dexos1 is predominant in areas that GM has to require 30 weight oil. Remember, you can always use dexos2 oil in a dexos1 car – dexos2 is a superset of dexos1 with additional detergents for diesel use and improved fuel economy.

It is unclear, still, if dexos2 does have a major horsepower loss vs dexos1… most tests so far are inconclusive, and point to it being a trivial tradeoff.

Legal: What you put in your car is your call. I’m obligated to say that you make your own decisions and that the safest oil for your car is typically the one stated in the manual that came with your car. I’m not responsible for your oil choices, both inside and outside of manufacturer specification.

Update: Unfortunately, Mobil just informed me that their European Car Formula is being discontinued in the United States. As I note in the updated article, that leaves us in a lurch here. It was the only generally-available 0w-40 that met GM LL-0-25 standard stateside, and most/all oil makers over here won’t label their 40 weight oils as dexos2. Please post in the comments if you can find a dexos2 oil that is 40 weight, and certified as such in the United States.