GM adds new dexos R approved oils

[nordique14]

I see the list of approved dexos R oils has increased since I last looked. As of 3/16/26

 

[jbawden]

I wonder how much this has to do with the L87 debacle? By that I mean, regular people are going to be annoyed that they have to buy Supercar for their T-Ball mobility device (now that Dexos R is the recommendation). I'm sticking with Supercar.

 

[hawk02]

I wonder how much this has to do with the L87 debacle? By that I mean, regular people are going to be annoyed that they have to buy Supercar for their T-Ball mobility device (now that Dexos R is the recommendation). I'm sticking with Supercar.

I understand the dealers are now using the Mobil 1 FS oil for changes in the 6.2L L87s because it’s less expensive than the Super Car oil. So yes, I think cost has a lot to do with the expanded list of Dexos R approved oil.

 

[Moffetts]

I didn’t know there was a 5w-50 version of M1 Supercar.

 

[RDATLTE]

I didn’t know there was a 5w-50 version of M1 Supercar.

Track oil for the ZL1 1LE.

 

[Moffetts]

Appears that the C8 Z06/ZR1 uses it as well.

 

[hawk02]

Track oil for the ZL1 1LE.

The ZL1 1LE oil weight for track days is 15W 50. 0W 40 is the oil weight for street use.

The 5W 50 is for the C8 Z06 & ZR1.

 

[RDATLTE]

The ZL1 1LE oil weight for track days is 15W 50. 0W 40 is the oil weight for street use.

The 5W 50 is for the C8 Z06 & ZR1.

You're correct. Sorry for the misinformation. I even checked my notes before posting. Obviously, not close enough.

 

[nordique14]

The ZL1 1LE oil weight for track days is 15W 50. 0W 40 is the oil weight for street use.

Is that only for the ZL1 1LE or all ZR1?

Since the 5BW also has the same LT4 engine, I am wondering if the same recommendation of 15W50 should be true for 5BW that see track use.

 

[SIR ICE]

According to a posting by GM Engineering a few years back in response to questions on the Camaro form, 15W50 is required 'do to the higher cornering loads when using the Goodyear 3R tires'.

It's been said that at 1 g cornering that the oil in the pan is at 45 degrees.

The Camaro ZLE is a wet sump while the Corvettes are day sump.

If that theory is applied to the LT4 wet sump in the CT5 BW, then yes 15W50 would be go to oil for track use.

 

[nordique14]

Thanks for the info. Weird that GM has not issued the same guidance for Precision Package 5BW as they come with Cup 2R tires that I would imagine are similar to the Goodyear 3R.

 

[SIR ICE]

Thanks for the info. Weird that GM has not issued the same guidance for Precision Package 5BW as they come with Cup 2R tires that I would imagine are similar to the Goodyear 3R.

Key word is 'weird'. I'm sure they have bigger fish to fry.

 

[RDATLTE]

According to a posting by GM Engineering a few years back in response to questions on the Camaro form, 15W50 is required 'do to the higher cornering loads when using the Goodyear 3R tires'.

It's been said that at 1 g cornering that the oil in the pan is at 45 degrees.

The Camaro ZLE is a wet sump while the Corvettes are day sump.

If that theory is applied to the LT4 wet sump in the CT5 BW, then yes 15W50 would be go to oil for track use.

I'd say especially with the PP with Cup 2s.

 

[hawk02]

According to a posting by GM Engineering a few years back in response to questions on the Camaro form, 15W50 is required 'do to the higher cornering loads when using the Goodyear 3R tires'.

It's been said that at 1 g cornering that the oil in the pan is at 45 degrees.

The Camaro ZLE is a wet sump while the Corvettes are day sump.

If that theory is applied to the LT4 wet sump in the CT5 BW, then yes 15W50 would be go to oil for track use.

The 15W-50 recommendation on the ZL1 1LE isn’t just about the Goodyear 3R tires—it’s the entire system working together. The 1LE has significantly more aero (downforce) and the Multimatic DSSV dampers allow the car to sustain higher lateral loads more consistently than the standard ZL1.

That combination is what pushes sustained cornering forces into a range where oil control in a wet sump becomes more critical, hence the heavier oil.

On the CT5-V Blackwing (including the Precision Package), the aero and suspension setup is much closer to the standard Blackwing than a ZL1 1LE. So sustained lateral G capability isn’t on the same level as the 1LE.

Given that, it makes sense that GM recommends 0W-40 for both street and track use on the Blackwing—similar to the base ZL1—rather than stepping up to 15W-50.

 

[jbawden]

Count me among the ones wondering how a slight increase in viscosity changes the physics of hot oil in the sump during high corner loads.

 

[hawk02]

Count me among the ones wondering how a slight increase in viscosity changes the physics of hot oil in the sump during high corner loads.

I wouldn’t call 15W-50 a slight increase over 0W-40 — it’s roughly 30–50% thicker at operating temp, which is exactly why GM specifies it for high lateral load conditions.

The real difference between the oil weights is in the high temperature, high shear (HTHS) values. A 15W-50 has ~20–30% higher HTHS, which means a much stronger oil film under the exact high-temp, high-shear conditions you get in sustained cornering.

 

[jbawden]

Whatever the percentage difference in viscosity is, I'm just curious how higher viscosity helps specifically in high lateral g-force scenarios. I get that higher viscosity might be beneficial under the general extreme conditions of track work. If the idea is better film strength under potential starvation issues, then there is a serious design flaw in the sump (I doubt this is the basis of the recommendation).

I'm not arguing over it, just wondering if it was a misinterpretation of why GM recommended the higher viscosity in the ZL1 or if there is something different about the LT4 in the BW like better oil cooling, baffling, etc (or GM did more research and determined 15w-50 un-necessary).

 

[hawk02]

Whatever the percentage difference in viscosity is, I'm just curious how higher viscosity helps specifically in high lateral g-force scenarios. I get that higher viscosity might be beneficial under the general extreme conditions of track work. If the idea is better film strength under potential starvation issues, then there is a serious design flaw in the sump (I doubt this is the basis of the recommendation).

I'm not arguing over it, just wondering if it was a misinterpretation of why GM recommended the higher viscosity in the ZL1 or if there is something different about the LT4 in the BW like better oil cooling, baffling, etc (or GM did more research and determined 15w-50 un-necessary).

I don’t think this is about a sump design flaw — it’s about oil behavior in a wet sump under sustained lateral G.

In long sweepers, even with good baffling, you get oil displacement, aeration, and high shear rates. So it’s not just “starvation vs no starvation” — it’s degradation of the oil’s effective viscosity and film quality.

That’s where HTHS matters. A 15W-50 has ~20–30% higher HTHS than a 0W-40, which means better film thickness and load capacity at the bearings under high temp/high shear.

So the higher viscosity isn’t fixing supply — it’s maintaining film stability under worst-case conditions. Dry sump systems don’t need that margin as much because they control aeration and pickup far better.

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