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M5 Guru (>2000 posts)
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Funny you should ask this. I posted essentially the same question arising in a different context last weekend and received no response. After some seriously deep searching in the archives of the board and some first-hand experimentation, I determined that 93C is about as hot as your Beast should get in, say, 85 degree weather and/or idling in an open garage for 5-10 minutes. 93C is the point at which my auxiliary fan kicked in. The secret menu test on the cluster showed the typical operating temp while in reasonably well-moving traffic with an ambient temperature around 80 degrees to average about 91C or 90C. This, I should point out, is with a two-speed Zionsville radiator and Spal electric fan setup, but posts on similar issues by board members over the years corroborate this.
Thus, I think the fluctuation you are experiencing is within the typical range. I will say that air pockets in the coolant can cause wild fluctuations in Ktemp, but are pretty easily (as least, in my limited experience) resolved by using the TIS venting technique, viz., ignition on position 2, heat on high, fan on relatively low, add coolant until appropriate level is hit (on a Zionsville expansion tank, about an inch below the mouth; on a stock expansion tank, up to the "cold" level, then crank engine and warm up to operating temp, turn off engine, allow to cool, then repeat until, when the engine is cool, no more coolant needs to be added. That eliminated the air pockets for me and stabilized my Ktemp pretty dramatically.
--Peter
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The Beast
2001 E39 M5 LeMans Blue with Black/Blue Sport Interior and Titanium Trim, ESS Supercharger, RMS In-Plenum Intercooler, RMS Plenum Plates and Custom-Bored 52mm Diameter "Shorty" Velocity Stacks, Dinan TBs and Headers, CNS Catback Exhaust, Evosport High-Flow Cats, Stoptech Trophy Sport Brakes (6-Pot Front/4-Pot Rear; 355 mm Rotors All Around), Dinan 3.45 Differential, Dinan LTW Flywheel, GC Coilovers (550 7" Front/325 10" Rear), Dinan Front and Rear Swaybars, Dinan Monoballs, Dinan Rear Wheels (18 x 9.5) All Around With 10mm Spacers and 90mm Wheel Studs, Michelin PS2s 275 35 18s All Around, UUC EVO3 SSK with DSSR, Voltphreaks VPR-S40P Endurance Battery (14 lbs.), Setrab 16-Row Oil Cooler, Dinan Under-Plenum Heat Exchanger Removal Kit, Vorsteiner Double-Sided CF Hood with Open Vents, CA CSL-Style CF Trunk Lid, Zionsville Super Duty Cooling System, Aquamist HFS-6 Meth Injection with Custom CF/Aluminum Trunk-Mounted Fuel Cell Designed by Howerton Engineering, XRP HS-79 Hosing, OKD Plasma Ignition Coils and Plug Boots, Smoked Hella Tailights, Clear-Corner Hella Euro Headlights, CA ACS-Style CF Front Splitters, Custom Stereo Using Stock HU, PLX Digital Gauges, V1/S1 Mounted in UGDO Location, Recaro Sportster CS Seats, Schroth 4-Pt Street Harnesses, Dinan Foglight Delete Kit, and Various Other Bits and Pieces
Coming Soon!
Hankook R-S3 285 35 18s All Around, EAS Competition Steering Wheel, TC Designs Roll Bar, Leather Eurodash, Full Leather Doorcards, TC Designs Rear Sway Bar Brackets, Rogue Stage 3 280mm Clutch with JB Racing LTW Flywheel, Dinan Differential Subframe Reinforcement, Stoptech Carbon Ceramic Rotors, Quad Head Laser Interceptor, Kenne Bell Boost-A-Pump
When the Motor Blows
Balanced and Blueprinted S62
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i turned the heat on pulled off 20 min later and coolant was 87 degrees C. 
Linear Mode
