High-Flow Engine Oil Cooler Thermostat, 215°F

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High-Flow Engine Oil Cooler Thermostat, 215°F

Improved Racing's Flow Series Motor Sport (FSM) oil thermostat is a universal solution that can be used with any oil cooler on any vehicle or industrial application flowing up to 20 GPM (75.71 LPM).

The device's unique, patented internal design (US patent 9,772,632) ensures a low pressure drop by placing the bypass valve mechanism completely out of the primary oil flow. This arrangement also allows for a compact design.High performance vehicles require large oil coolers to ensure that the oil does not overheat during strenuous use. These coolers also introduce the danger of over-cooling the oil and delaying engine warm-up, resulting in horsepower loss, excessive engine wear and reduced gas mileage. Oil thermostats perform the critical function of bypassing the oil cooler until the oil has reached its minimum operating temperature.

The thermostat features female -10AN O-ring boss threads and is available with optional fittings in 3/8" or 1/2'' hose barb or AN fittings in -6AN, -8AN, -10AN, or -12AN. The included brackets allow for multiple mounting options.

Supersedes part numbers ENV-100 and EUN-1000.


Features and Benefits

  • Reduces excessive engine wear and horsepower losses while improving gas mileage by preventing oil temperatures from dropping below optimal levels
  • Maintains a minimum fluid temperature according to the typical stabilization temp in the table below, +/- 2°F (+/- 1°C)
  • Patented, high flow, low pressure drop design locates the valve assembly completely out of the primary fluid flow
  • Allows a small percentage (less than 10%) of fluid to continually circulate through the cooler to eliminate air pockets and prevent cold fluid trapped in the cooler from shocking the system
  • Thermostat can never fail in such a way that fluid flow is blocked
  • Rebuildable
  • 6061-T6 billet aluminum construction with black MIL-A-8625 Type II anodized finish
  • Lightweight at just 12.7 ounces (360g) without brackets or fittings

Temperature Rating Specifications

Part Number Typical Stabilization Temp Activation Temp Full Flow Temp Recommended Application
FSM-145 145ºF (63ºC) 140ºF (60ºC) 163ºF (73ºC) Trans & Diff Fluid
FSM-165 165ºF (74ºC) 160ºF (71ºC) 181ºF (83ºC) Trans & Diff Fluid
FSM-185 185ºF (85ºC) 180ºF (82ºC) 203ºF (95ºC) Engine Oil (Street & Strip)
FSM-205 205ºF (96ºC) 200ºF (93ºC) 221ºF (105ºC) Engine Oil (Street & Strip)
FSM-215 215ºF (102ºC) 212ºF (100ºC) 233ºF (112ºC) Engine Oil (Road Racing)

Valve assembly is housed completely between the two ports. No valves, springs, or thermal motor interrupting the primary oil flow!

Compact dimensions (shown in inches)

Brackets allow for multiple mounting configurations

Available with 3/8" or 1/2'' hose barb fittings or AN fittings in -6AN, -8AN, -10AN, or -12AN


  • Engine, transmission, differential, and industrial fluid cooling applications flowing up to 20 GPM (75.71 LPM)
  • Passenger car automotive, marine, and experimental aircraft engine oil cooling systems
  • Automotive and truck power steering fluid cooling systems
  • Diesel and gas truck transmission fluid cooling systems
  • Diesel and gas truck differential and transfer case fluid cooling systems
  • Not for use with corrosive fluids. If used with water, a distilled water solution with a lubricant such as ethylene glycol must be used.


  • 1x Remote thermostat block
  • 2x Zinc-plated steel mounting brackets and screws


Part #
FSM Configurator
Improved Racing
Part Weight
12.7 oz (360g)
Primary Material
6061-T6 aluminum
Type II Anodized
Minimum Operating Temperature
-40°F (-40°C)
Maximum Operating Temperature
302°F (150°C)
Inlet Port Size
-10AN O-Ring Boss Female
Outlet Port Size
-10AN O-Ring Boss Female
Maximum Operating Pressure
300 psi (20.68 bar)
Max Recommended Flow Rate
Up to 20 GPM (76 LPM)
Fluid Compatibility
Engine oil
Power Steering Fluid
Transmission fluid
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