So this came up in another forum relating to the JLR STJLR.51.5122 being the same spec (or similar enough) to Euro specification ACEA C5 to be equivalent. True or false, or is the JLR spec inclusive of other matters than the C5?

"In essence, JLR STJLR.51.5122 is often associated with and considered equivalent to the ACEA C5 engine oil specification. Here's why:

• Many oil brands list both specifications together. When you look at product descriptions for oils that meet JLR STJLR.51.5122, you'll frequently see ACEA C5 listed alongside it, indicating compatibility or equivalence.
• Both specifications share characteristics. JLR STJLR.51.5122 is a specific Jaguar Land Rover standard, while ACEA C5 is a broader European standard. Both are geared towards fuel efficiency and are suitable for modern engines requiring low-viscosity, mid-SAPS oils (0W-20 or 5W-20) with a specific HTHS (High Temperature High Shear) viscosity range.
• ACEA C5 oils can be used as a substitute. If you can't find an oil specifically approved to JLR STJLR.51.5122, an ACEA C5 SAE 0W20 oil can be used instead, as it is similar in performance.

"In summary, while not exactly the same, oils meeting the JLR STJLR.51.5122 specification are generally also categorized as ACEA C5 oils and vice versa."


And, interestingly, here's another answer that says they're not the same, but specifies a Castrol oil that is spec'd both ways:

No, ACEA C5 is not the same as the JLR (Jaguar Land Rover) specification.While ACEA C5 is a performance specification for engine oils that is commonly referenced by JLR, it is not identical. JLR has its own specific engine oil specifications, such as STJLR.03.5006 and STJLR.51.5122, which may have additional requirements beyond ACEA C5.

Here's a more detailed explanation:

• ACEA C5: This is a European Automobile Manufacturers' Association (ACEA) specification for lower SAPS (Sulphated Ash, Phosphorus, and Sulphur) lubricants, designed for use in gasoline and light-duty diesel engines with aftertreatment systems like DPFs and TWCs. It emphasizes fuel economy and extended drain intervals.
• JLR Specifications (e.g., STJLR.03.5006, STJLR.51.5122): Jaguar Land Rover has its own specific engine oil requirements, often denoted by a unique part number or specification. These specifications may align with ACEA C5 in terms of viscosity (e.g., 0W-20) and other performance characteristics, but they can also include additional requirements or testing procedures specific to JLR engines.
• Relationship:
  Many JLR engines that require a 0W-20 oil, for example, may specify a lubricant that also meets ACEA C5 and/or has a JLR approval. However, it's crucial to consult the vehicle's owner's manual or service information for the specific JLR oil specification required for your vehicle, as it may be more restrictive than a general ACEA C5 recommendation.
• Example:
  The Castrol EDGE Professional E C5 0W-20 is an example of an oil that meets both the ACEA C5 specification and the JLR STJLR.03.5006 specification. [Panthera: This is confirmed in castrol's data sheet for this oil.]

In essence, while ACEA C5 is a relevant standard, it's not the sole determinant of what oil is suitable for a Jaguar or Land Rover. Always verify the specific JLR-approved oil for your model.

And FWIW, a dialogue at Bob is the Oil Guy: https://bobistheoilguy.com/forums/th...1-5122.360312/

Panthera.

 

all the c5 oils have approvals from more competent manufacturers

either way run 0w40 a3/b4 if you are not after fuel economy

 

I’m running 5w-50 as I keep the revs pretty high/push the car. Seems to like it so far.

 

You didn't say which engine you've got or mileage, but for street use, that viscosity's way too high. For the 4.2 with average miles 30-40 fine, for the later AJs, 5.0 and 3.0 litre, again mileage dependent, 20-40 would be appropriate. As an engine wears from use, slightly increasing viscosity can help with lubrication as clearances increase.