Mosselman MSL N54 85C Oil Thermostat for BMW 1M, 135i, 335i & Z4 35i (E82 E90 E92 E93 E89) - Billet Plug-and-Play Upgrade

Keep your N54 running cooler and happier with an 85°C direct-fit oil temp regulator

If your E82, E90, E91, E92, E93 or E89 with the twin‑turbo straight‑six is seeing hot oil on spirited drives or track days, this 85°C performance thermostat is the proven answer. By opening earlier than the factory unit, it stabilises lubricant temperature around the mid‑90s to low‑100s °C range, helping resist heat soak, timing pull and inconsistent performance while still giving proper warm‑up on cold mornings.

Built in a CNC‑machined billet aluminium housing with a genuine thermostat element, this is a simple bolt‑on that delivers a meaningful reliability gain for both tuned and standard cars. We have fitted this part on numerous customer cars and our own shop vehicles and the feedback is consistently excellent — cooler, more stable oil temps and greater confidence on fast road and track.

Why this 85°C thermostat is a smart upgrade

• Lower operating window versus stock helps curb heat soak and maintain consistent power delivery
• Real wax‑stat control for correct warm‑up in British weather, not an always‑open bypass
• Billet aluminium body for strength, durability and a premium finish
• Direct‑fit, plug‑in install typically around 30 minutes with basic tools
• Ideal for Stage 1 and Stage 2 cars, hard road use and track days

What you get

• 1 x Mosselman MSL 85°C thermostat assembly for N54

Recommended extras — sold separately:

• MSL Installation Kit — fresh O‑rings for the oil lines and oil filter housing gasket to prevent leaks
• MSL Titanium GR5 Hex‑Race Bolt Set — three M8x25 fasteners for a clean, corrosion‑resistant finish

Fitment

• BMW 135i or 135is E82 with N54
• BMW 135i E82 with N55 — uses the N54‑style thermostat in this chassis
• BMW 1M Coupe E82 with N54
• BMW 335i E90 E91 E92 E93 with N54
• BMW 335i E90 E91 E92 E93 with N55 — requires the N54‑type thermostat in these models
• BMW Z4 35i and 35is E89 with N54, including LCI

Real‑world results you can feel

Owners report a drop of roughly 20°C in operating oil temperature versus factory calibration, typically stabilising around 95 to 105°C depending on model and use. That means stronger oil film, reduced risk of limp mode from excessive heat and more consistent lap‑after‑lap performance.

Fitting service

Want it installed professionally? Book with MJ Modifications in Warwickshire. Email info@mjmodifications.co.uk for a quote and availability. An engine oil change is required during installation.

Compatibility check before dispatch

We verify compatibility prior to shipping. Add your UK registration or the last 7 of your VIN at checkout so we can confirm the correct part for your car.

Part number

OTN54.T85

Search terms our customers use

BMW N54 cooler stat, 85 degree oil thermostat, E82 1 Series oil temp fix, E90 E92 E93 oil cooling upgrade, Z4 35i thermostat housing, N54 engine oil temperature control, track day oil cooling mod, direct‑fit billet thermostat, BMW turbo six heat management, BMW 1M oil temp regulator, 135i oil cooler solution, 335i oil temperature upgrade, E89 Z4 oil thermostat replacement.

Notes

• Oil change required at the same time as fitting
• Installation Kit and Titanium Bolt Set are optional but recommended