GM Is Making An Extremely Tiny (But Important) Change To Its L87 Engine Fix After The Feds Launched An Investigation Into Its Recall

For the past year or so, General Motors’ line of full-size SUVs and 1/4-ton pickup trucks equipped with the brand’s optional 6.2-liter “L87” pushrod V8 engine has revealed itself as being plagued with issues. It started in January 2025, when the National Highway Traffic Safety Administration launched an investigation into over 870,000 vehicles equipped with the engine due to reports of premature, major failures.

Three months later, GM recalled nearly 600,000 of those vehicles, with the brand revealing it had received no fewer than 28,000 complaints over the issue. And eight months after that, the NHTSA launched another investigation into whether GM’s recall fix “failed” after the government agency kept receiving complaints, even from vehicles that got the recall work done.

Now, following that investigation’s launch, GM has made an extremely tiny (but important) update to how it wants the L87’s recalls performed: It’s changing the type of oil dealers will be instructed to use.

Here’s Where We’re At

To catch you up, GM’s April 2025 recall for the L87 is a two-fold affair. Part one involves an inspection, and if the engine passes that inspection, technicians move on to part two, an oil change with a new type of oil. Here’s the gist of it, from the last time I wrote about this subject:

For a remedy, dealers were instructed to inspect the 6.2’s internals to look for early signs of failure. If the dealer determined any signs of a potential failure, they were to repair the engine or replace it entirely, as necessary. Repaired engines would get connecting rods and crankshafts “produced after the suppliers’ suspect manufacturing window,” according to GM (via the recall doc). GM doesn’t say exactly what was changed, only that a “series of crankshaft and connecting rod manufacturing improvements implemented on or before June 1, 2024, addressed contamination and quality issues.”

If there were no signs of failure, the dealer would replace the oil with a higher-viscosity oil and replace the oil filter. Vehicles were also given a new oil cap with the updated oil weight printed on the top.

The L87 originally came with 0W-20-weight oil from the factory, but that gets replaced with 0W-40 with the recall. Specifically, GM instructed dealers to replace the old oil with Mobil 1 Supercar 0W-40. As of today, though, GM wants dealers to start using a different kind of 0W-40.

Here’s What’s Changing Specifically

In a series of service bulletins sent to dealerships nationwide and seen by GM Authority, General Motors is now instructing mechanics to use Mobil 1 FS 0W-40, rather than the Supercar blend. A representative for the brand confirmed the news to The Autopian via email and provided the following statement as to why it made the switch:

GM revised its bulletin to specify the use of Mobil 1 FS 0W-40 because of its wide availability, price point and performance criteria that meet the needs of the recall remedy.

According to GM Authority, the company is instructing dealers to switch over to the new oil once they run out of the fancy Supercar stuff. From the article:

Until now, dealers have been using Mobil 1 Supercar 0W-40 oil for these repairs. However, GM has now directed dealers to use Mobil 1 FS 0W-40 oil once the existing Supercar oil inventory has been depleted. Critically, dealers have also been notified that they will soon no longer be eligible to claim the $50 reimbursement previously offered to offset the higher cost of the Supercar oil compared to the FS 0W-40 and the original 0W-20 specification.

Why Is It Important?

Considering GM Authority’s reporting and GM’s comment above, it’s very likely the company is making the switch because simply Mobil 1’s FS is cheaper and easier to get ahold of than the Supercar blend, while still fulfilling the same parameters engineers needed for the recall fix. But I think it’s still worth digging into what’s changing here.

Oil is the lifeblood of any engine, and even minor changes in its formula can have lasting effects, not only on reliability but also on performance and fuel economy. While these FS and Supercar blends may have the same oil weight, they differ on some key levels.

Going by Mobil 1’s website, the outgoing Supercar blend is described as something you might use in a sports car rather than a truck or SUV:

Mobil 1™ Supercar 0W-40 is an advanced full synthetic motor oil specifically designed for high performance cars to provide exceptional cleaning power and wear protection, and deliver outstanding overall performance. Mobil 1™ Supercar 0W-40 is proven in high performance North American sports cars and suitable for use in everyday driving and high performance track events.

Digging deeper into Mobil 1’s product guide, the company specifically mentions Supercar as suitable for “Corvettes and Camaros that call for 0W-40 oil.” The FS blend, meanwhile, sounds like it’s a bit better suited to daily driver duty. From Mobil 1’s website:

Mobil 1™ FS 0W-40 advanced full synthetic motor oil is engineered to deliver excellent all-around performance in gasoline and diesel engines (without Diesel Particulate Filters or DPFs) with the latest technological advancements. Mobil 1 FS 0W-40 motor oil provides exceptional cleaning power and wear protection to keep your engine running like new in most driving conditions, from mild to extreme.

Still, both of these descriptions are pretty vague and don’t actually get into the nitty-gritty details of how the two oils differ. Thankfully, that product guide I linked earlier also spills the beans on some differences in additives. All mass-produced engine oils have their own unique blend of additives, mixing stuff like antioxidants, detergents, and anti-wear agents to improve the oil’s effectiveness and longevity.

While Mobil 1 doesn’t publish its exact blends online, there are a few useful nuggets of info. For instance, the FS blend of its 0W-40 oil contains slightly more phosphorus and zinc than the Supercar blend, according to the company’s chart. Both of those materials are used as anti-wear additives, according to Valvoline:

Phosphorus is a powerful additive that minimizes friction and reduces wear on the moving parts of the engine.

Phosphorus is most commonly used in zinc ester formulas, with Zinc Diakyldiphosphosphate (ZDDP) being the most common additive. It creates a protective film on metal parts and protects the engine parts from friction and wear.

Some other sources of phosphorus in engine oil are corrosion inhibitors, friction modifiers, antioxidants, and extreme pressure additives.

While Mobil 1 doesn’t reveal calcium levels on its website, the folks over in the Bob Is The Oil Guy forums, where people obsess about oil science 24/7, have reportedly discovered that the FS blend has slightly less calcium than the Supercar blend. Calcium is used in oil as a detergent additive, meant to keep deposits from forming and neutralize acids, according to MachineryLubrication.com.

Mobil 1 also labels the FS blend as meant for “high HT/HS applications.” In the world of engine oil, HT/HS means High Temperature, High Shear. Basically, this is the measure of how well the oil can function while being subjected to the stresses of an engine. From the Spanish oil producer Repsol:

Why should we care about HTHS viscosity? The truth is that it is crucial for three reasons:

• The high engine temperatures. Internal combustion engines generate a lot of heat during their operation. In this regard, HTHS viscosity is relevant because it tells us how the lubricant resists the reduction of its protective film under these extreme conditions.

• High loads and shear rates. The engine’s moving parts experience high shear rates due to the rotation and interaction of the components. In this situation, the HTHS viscosity provides information on how the lubricant forms the right film to protect the various parts from this wear.

• The balance between fuel efficiency and durability of the engine. Here is where the balance between HTHS viscosity and other properties of the oil comes into play, such as thermal stability or resistance to wear.

Repsol goes on to say that an oil with high HTHS viscosity can maintain its function and prevent premature wear, but at the cost of greater friction, which increases fuel consumption. That’s because the more resistance an oil causes within an engine, the more drag it produces on its moving parts. That means it takes more effort (a.k.a., more burning fuel) from the engine to spin itself.

What does all of this mean for GM’s L87? Without knowing all of the exact differences between the oils or the company’s thinking behind the switch, it’s tough to tell for sure. But this data suggests that the new oil has slightly more anti-wear properties and slightly less cleaning properties than the outgoing stuff. Take that information how you’d like.

The high HTHS labeling might be a good or a bad thing, depending on whether you value reliability or fuel economy more. Seeing as how the oil weight is the same between the two blends, I suspect any change in fuel economy will be extremely minor. Personally, I’d take a working, slightly inefficient engine over more wear and more efficiency every time.

Top image: General Motors