Why we switched our 718 Cayman S from Mobil 1 to Motul

Our shop car was a 2021 718 Cayman S with the 2.5 turbo flat-four (MA2). We didn't baby it. It was a daily driver that also ran about 15 HPDE track days and 15 autocross days a year, and it went from the PCA student run group in 2022 to the advanced group in 2025. We pulled a used oil sample at nearly every change and sent it to the lab.

The short version: the dealer-fill Mobil 1 0W-40 came back thin and oxidized. Motul 8100 X-clean Gen2 5W-40 came back holding its viscosity, with single-digit wear metals, even as the driving got harder — including on the last three fills, which turned out to be Motul's updated formula that no longer carried Porsche C40.

Here's the data. No marketing, just lab numbers.

How we tested

• Car: 2021 Porsche 718 Cayman S, MA2 2.5L turbo, PDK.
• Use: commuting and weekend drives (~30k miles per year), plus about 15 HPDE track days and 15 autocrosses a year. The driver moved from the PCA student run group (2022) to advanced (2025). That means the hardest laps landed on the later, higher-mileage Motul samples.
• Spec: Porsche C40 is the approval our car calls for. The Mobil 1 carried it. The Motul carried it on every sample through 81,435 miles. From the fill at about 87,058 miles on, the bottles were Motul's updated X-clean Gen2 formula, which did not carry C40. More on that below.
• Intervals: every 5,300–6,300 miles, well short of the factory interval. That's on purpose for a car that sees the track.
• Lab: SPEEDiagnostix, same lab every time, so the trend is apples to apples.
• Coverage: 9 engine oil samples taken from 46,934 to 103,951 miles on the odometer. The oil history is simple: Mobil 1 at every change up to 52,212 miles, then Motul at every change from 52,212 to 103,951. That's 51,739 continuous miles on Motul. We sampled 7 of its 9 fills, and both fills we skipped were Motul too.

What the Mobil 1 showed

We started on Mobil 1 0W-40, the Porsche C40-approved oil dealers put in these cars. For us that was either Mobil 1 ESP X3 0W-40 or ESP X4 0W-40. Both carry Porsche C40, and we don't know which one went in. That stretch included track days and autocross too. Two back-to-back samples, at 46,934 and 52,212 miles:

• Viscosity: 11.5 cSt at 100°C both times. That's below the 12.5 cSt floor for a 40-weight. Mobil lists these oils at 13.9 cSt (ESP X4) and 14.1 cSt (ESP X3) new, so ours was coming out roughly 17–18% thinner than it went in. Per the lab: "Viscosity is below grade, which is typical for Mobil 1 0W-40."
• Oxidation: 39.4, then 26.8. Every Motul sample after that ran 13.7–17.0.
• Wear: the second sample went to 5 ppm per 1,000 miles, up from 4. Aluminum went from 6 to 11 ppm.

The lab marked the second report Caution: "Viscosity is still below grade, and the oxidation level indicates degradation. The wear rate has also increased." They recommended moving to Motul or Driven, the oils where they see the lowest wear metals.

So we switched, at 52,212 miles, and never went back.

What the Motul showed

We ran Motul 8100 X-clean Gen2 5W-40. The samples from 64,459 to 81,435 miles were the version that carried Porsche C40 approval. The last three (92,727 to 103,951 miles) were the updated formula, which didn't.

• First sampled Motul fill: 11.9 cSt (64,459 miles). This was actually the second Motul fill, since we didn't sample the first one (52,212–58,200). The lab read it as Mobil 1 carryover: "There's residual of the old Mobil 1 even when you do an oil change." Magnesium and moly, both heavy in the Mobil 1, did keep falling over the next two changes (magnesium 163 → 62 → 28 ppm, moly 16 → 5 → 2). But with a full Motul change in between, carryover is a less clean explanation than it sounds. Either way, it's the only Motul sample under 12.3.
• Every fill after that: 12.3, 12.3, 12.6, 12.3, 12.3, 12.3 cSt, from 69,990 to 103,951 miles. That's 0.8–1.1 cSt thicker at drain than the Mobil 1. Against the 13.5 cSt new-oil spec on Motul's C40-era data sheet, it lost about 9% over a change. (We don't have a separate new-oil figure for the updated formula, so treat that as approximate for the last three samples.) The Mobil 1 lost roughly 17–18%.
• Oxidation: 13.7–17.0, averaging 15.1. That's roughly half of what the Mobil 1 showed (33.1 average).
• Wear: 3–4 ppm per 1,000 miles, with total wear metals of 17–25 ppm. Iron stayed at 8–14, aluminum at 4–9, copper at 1–2, lead at 0–1.
• It didn't fade as the driving got harder. The last three samples (92,727 to 103,951 miles) came from the busiest track years and the move to the advanced run group. These were also the updated, non-C40 formula. They read 12.3 cSt each time, with oxidation at 15.1–15.3 and wear at 3–3.5 ppm per 1,000 miles — essentially the same as the C40 version. On the November 2024 sample, the lab said "Single digit wear metals are very good." On the next one, it said "The drain interval can be extended."

Straight talk: the Motul still sits a hair under the 12.5 cSt line on most samples. The lab calls it "barely below grade," and it crossed the line once (12.6). This isn't a magic oil that drains like new. It held up noticeably better than the dealer-fill Mobil 1, in this engine, at this interval, under track use.

The numbers

Wear metals in ppm. Lab: SPEEDiagnostix. SAE 40 viscosity range is 12.5–16.3 cSt at 100°C. Motul fills ending at about 58,200 and 87,058 miles were not sampled. From the fill at about 87,058 miles on, the Motul was the updated X-clean Gen2 formula without Porsche C40 approval; the lab saw the additive mix change starting with the Aug 2024 sample (calcium about 1,050–1,095 ppm vs. 1,713–1,753, magnesium 332–385 vs. 18–28, moly 53–61 vs. 1–2 on the two fills before). *Nov 2023 sample was caught at the end of the drain, not mid-stream, which can skew metals high.

What we didn't see

Fair is fair:

• No engine was hurt on Mobil 1. Wear on the Mobil 1 was in normal range. The case against it is thin viscosity at drain and higher oxidation, not damage.
• Two Mobil 1 samples is a short run. We switched on the lab's advice after the Caution report. We didn't keep running it to see where the trend went.
• We didn't send the lab any fresh oil. The "% thinner" numbers compare our used samples to the manufacturers' published new-oil specs, not to a bottle tested on the same machine.
• Fuel dilution stayed between 0.3% and 1.34% on both oils, and the lab never flagged it. It ran about 1.25% on the last three Motul samples, so we watched it.

The bottle we ran isn't the bottle on the shelf anymore

This part matters if you go shopping. Motul has updated the formula of 8100 X-clean Gen2 5W-40, and the updated version no longer carries Porsche C40. Motul says so itself. To fill the gap, it launched Motul Specific C40 5W-40 in early 2025, a 5W-40 built specifically for Porsche C40 engines. That's what we stock — Motul Specific C40 5W-40, in 5-liter jugs and 1-liter bottles — and what we'd put in a 2017–2020 C40 718 today. For 2021 and newer cars, see the viscosity note below.

Full disclosure: our last three samples (92,727, 98,176, and 103,951 miles) were that updated formula. The bottles from the fill at about 87,058 miles on didn't carry the C40 approval, and we only caught that after the fact. The lab data shows the change too: starting with the Aug 2024 sample, calcium dropped to about 1,050–1,095 ppm from 1,713–1,753, magnesium jumped to 332–385 from 18–28, and moly went to 53–61 from 1–2. The results barely moved: 12.3 cSt, oxidation 15.1–15.3, wear 3–3.5 ppm per 1,000 miles, essentially the same as the C40 version. That's three samples in one engine, not a reason to run a non-C40 oil in a C40 car. It's exactly why we now stock Specific C40, and why you should read the label instead of going by the product name.

To be clear: Specific C40 is a different formula from both versions of X-clean Gen2 we sampled. Our numbers show how Motul's X-clean Gen2 5W-40 held up in this engine. They aren't a lab test of Specific C40 itself. If you find old stock of X-clean Gen2, check the label for "Porsche C40." If it's not there, it's not a C40 oil.

Should you switch?

Porsche's approved-oil bulletins list C40 for the turbo four-cylinder 718 Boxster and Cayman (2.0 base and T, 2.5 S, and the 2.5 GTS through MY2020) and for the GTS 4.0. The GT4 RS and Spyder RS call for C40 GT instead. Requirements vary by model year, so your manual has the final word.

One model-year catch on viscosity. For cars through MY2020, Porsche's C40 allocation allows 0W-40 or 5W-40. From MY2021 on, the allocation defines C40 as 0W-40 only. Our car is a 2021, so strictly by the book it should have run a C40 0W-40. We ran 5W-40 by choice for a heavily tracked car. That was our call, not a recommendation for yours. If your 718 is a 2017–2020, Specific C40 5W-40 is our pick. If it's a 2021 or newer, and especially if it's under warranty, run a C40-approved 0W-40 as your manual says.

If your 718's manual calls for Porsche C40, here's what we'd do:

1. Run the approval your car calls for, and check the bottle. Check your owner's manual for the approval and the viscosity grade, then check the label, because formulas change under the same name. Ours did: the X-clean Gen2 we bought later in the test no longer carried C40, which is why we moved to stocking Motul Specific C40. Porsche C40 is not backward-compatible with A40, C30, or C20, and C40 is not C40 GT. A great A40 oil is still the wrong oil for a C40 engine. We practice what we preach: our current GT4 RS is under warranty and its engine calls for C40 GT, so it gets Porsche C40 GT oil. No experimenting with non-certified oils like Motul 300V on that car.
2. Shorten the interval if you track it. Our 5,300–6,300-mile changes held wear at 3–4 ppm per 1,000 miles through about 15 track days and 15 autocrosses a year.
3. Sample your own oil. A UOA costs less than a tank of premium and tells you exactly what your engine is doing. One sample is a snapshot. Three is a trend.

Questions about which oil fits your car? Email us at info@ltbracing.com. We'll match it to your exact chassis.

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