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The N55 is a fantastic engine — punchy, tunable, and packed with potential. But there's one annoying trait that crops up time and time again: it runs hot. We're talking 125–130°C oil temps in stop-start traffic or during spirited runs, even on a mild day. BMW will tell you it's "within spec." But let’s be honest — if you’re tuned or tracking your car, that’s a ticking time bomb for oil breakdown and long-term engine wear.
The N55 is actually designed to run hot from the factory—higher oil temps reduce viscosity, which means fewer parasitic losses and better efficiency. That’s great for daily driving and emissions. But the moment you start pushing the car hard (who would ever thrash an M-Lite, right?), the factory setup starts to fall short. The stock thermostat doesn’t even begin to open until 110°C, and by then, you're already flirting with heat soak. The result? Power loss at best, or a cooked engine at worst.
This isn’t just limited to the N55—it’s a common trait across BMW’s N-series engines. While the S55 and N55 are especially prone to heat issues under load, similar patterns show up in the N54 and others when pushed beyond factory-intended use.
There are a few key reasons:
BMW says it’s fine, but repeated high-temp cycles aren’t ideal for oil life or engine bearings — especially on tuned cars.
If you want to bring those temps under control without a full cooler retrofit, a lower-temp oil thermostat is your first line of defence. One of the most trusted options on the market is the Mosselman Oil Thermostat for the N55.
If you’re still getting toasty, consider:
If you’re seeing 125°C+ oil temps regularly—especially on a tuned or hard-driven N55—don’t ignore it. The Mosselman N55 Oil Thermostat Upgrade is a simple, plug-and-play solution that keeps your oil temps in check, your engine protected, and your BMW ready to perform. It fits like OEM, works flawlessly, and helps your turbo motor stay cooler under pressure.
You can grab yours now at ML Performance, and if you want to get a quick intro to the part, check out this quick video by Xatrix on Instagram.
Your N55 wants to party—just make sure it doesn’t overheat at the rave.
