Motul 300V 10W-40 Competition Full Synthetic Motor Oil 2L Bottle

IAG's engine building document actually recommends Motul 10W-40 for all of their engines for E85 applications (1500mi interval, compared to 5W-40 and 3000mi interval for gasoline). Well... I wasn't really informed of this till I came across the doc earlier this year... Here's my oil report of me learning the hard way why 10W-40 is needed.

First, note that this is MY particular engine, do NOT compare my numbers directly with your engine's numbers and oil results. The importance isn't my numbers vs your numbers, but rather the trend in the numbers in itself. I'll try to explain this in a way that people unfamiliar with oil test results can digest.

There are 3 oil samples on this report. The rightmost sample (from 6/8/2025) was a sample of Motul X-cess Gen 2 5W-40 I ran for 8 months and 3.3k mi. You can see they bolded the iron, copper, and lead wear metals as they were basically 10x the amount of the normal wear from an EJ257, these are all bearing materials hinting at bearing damage and possibly, eventually, a spun bearing/rod knock/toasted engine.

At the bottom section, you can see the actual viscosity of the oil measured with the SUS and cSt value. Essentially, the oil grade of that sample has already fallen to 30 grade oil (like 5W-30) at the end of 8 months and 3k mi. While 30 grade oil is tolerable for an OEM block (and even then some people have recommended to move to 40 grade for protection, again depends on your specific application and test results), a built block with forged internals that are more suspectable to thermal expansion and hence have higher piston-wall tolerances like my IAG 550 will NEED 40 grade, as you can tell by the ridiculous amount of wear metals.

The second sample (done on 8/16/2025), showed wear metals down by half. HOWEVER, this was when my road trip took place, so about 1300 miles of that 1900mi sample was all freeway miles, ran on pump gas, NOT E85, in the summer, and ONLY through the course of 2 months, as opposed to 8 months of cold starts in the winter and daily driving from the previous sample, and yet wear metals only went down by half. Viscosity at the end of the 1900mi was still within 40 grade oil specs, but was relatively on the low end of it already.

The most recent sample (12/7/2025) is of this product, the Motul 300V 10W-40. This was ran over the course of 4 months with a lot of cold starts and during the cold of autumn/winter, and a lot of hard pulls.

There's a bunch to unpack here so first is the wear metals. EVERY wear metal is down compared to the previous sample DESPITE running it for longer, running it on only E85 (more moisture/dilution-prone, higher power/stress), and running it rougher (mountain runs, redline pulls every other day warmed up), with similar mileage of 1600 vs 1900. Obviously from this alone, you can see there's more engine protection in this oil than Motul's 5W-40.

If you want to look at WHY, one of the big things is moly. Previous samples of Motul's 5W-40 only had ~60 units of moly in it, while this 300V had an insane ~10x of that at 500 units.

The other thing is, even after near 4 months of use, the oil viscosity of this 10W-40 is still at an insane 14.45 cSt, WELL within the range of a 40 grade oil, and a big step up from the original sample of also a 40 grade oil (the Gen2 X-cess 5W-40) which was at 10.92 cSt (30 grade oil specs), and even much better than the previous sample (12.33 cSt) that was ran for half the time as this 300V, much less cold starts, on mostly pump gas, highway miles rather than stop and go and pulls/hard cornering.

So without a doubt, for my IAG 550 block, this 10W-40 is the way to go (as IAG correctly recommends) and I highly recommend that you follow their recommendations too if you're also running E85 on an IAG block.

If you're running on E85, on an OEM block, or another brand of forged blocks, try submitting an oil sample to see if wear metals and viscosity looks good, if they are, keep sending it as it is, if not, definitely recommend switching to this oil with more frequent oil changes.

Sidenote: if you read Blackstones comments, they're attributing my trend mostly to flushing out engine break-in materials (I did perform 4 oil changes using Motul 10W-40 breakin oil before the 5k mark) most likely because they didn't see HOW the car was being driven between the 1st and 2nd sample. I personally would attribute the first wear metal drop to 1/4th the driving time, mostly on highway in the summer on pump gas rather than the oil doing a good job protecting the engine and flushing out old gunk, as it still produced a very large amount of wear metals compared to normal.