Thermostat mod for E39/E38/E53 with M62 / M62TU:
- M62B35, M62TUB35
- M62B44, M62TUB44
BMW M62 engine is one of the first BMW engines that is running on higher than 105oC coolant temperature. The main goal of BMW engineers was decreasing the emissions levels and better fuel economy. Unfortunately, this system leads to a very small change in emissions and fuel economy, but causes almost all of M62 deceases – faster wearing of all the gaskets, problems with all water connections and hoses, issues with wires, located in the engine bay area.
M62’s thermostat is equipped with an internal heater which is designed to be controlled by your DME (engine control module).
When your car’s DME turns the heater ON, it makes the thermostat open early, not after 105°C reaching, but around 94°C, that’s how your DME can control your car’s coolant temperature.
Unfortunately DME turns on/off thermostat’s heater only after reaching one of the following conditions:
1. Coolant temperature above 110oC.
2. Full load range (sporty driving).
Here is the Control characteristics of “characteristic map cooling” of your M62 OEM cooling system (how it works from the factory):
|1||ON – Characteristic curve of a 110 o C thermostat|
|2||Characteristic curve of a characteristic map thermostat|
|3||OFF – Characteristic curve of an 85 o C thermostat|
|4||OFF – Partial load range|
|5||ON – Full load range (sporty driving)|
|6||OFF – Partial load range|
Thermostat mod shares similar method of controlling coolant temperature, it turns ON/OFF your thermostat internal heater, but it turns it ON much early and continuously. You can choose when (on what condition) would you like to get your heater turned on: after user defined time delay since applying 12V to Thermostat mod OR after reaching specified coolant temperature read out via IBUS. If you choose “time delay” option, you can even miss the step with IBUS connecting, the module will control your thermostat heater even without IBUS supplying. But if you choose Thermostat mod to turn on thermostat heater on temperature reaching, you definitely need to supply Thermostat mod with IBUS, otherwise it won’t know what’s your coolant temperature.
Thermostat mod installation into your car:
To install your Thermostat mod, you must connect its wires to 4 wires from your car’s wire harness: 12V; GND (ground); I/K-BUS; GND controlled wire of your thermostat connector.
Please use the following wiring diagram to connect Thermostat mod into your car:
Thermostat mod——————————————————–Car wire harness:
*If using IBUS method (function3 option2), connect the red wire to terminal R (12V ACC).
**If using TIME delay method (function3 option1), connect the red wire to terminal15 (12V switched).
Ground source in E-series is usually brown wire or brown wire with black stripe, but please confirm with multimeter.
I-BUS wire in E-series is usually white wire with gray stripe and yellow dots.
White thick wire—————————————————————–“GND controlled wire of your thermostat connector X6279 pin1 (brown-white on M62; white on M62TU). Please cut that wire and then connect Thermostat mod control wire to that part of the wire which will stay connected to the thermostat. You may just leave the other end of the wire (the one that goes to your DME) disconnected or you can put 500-1000 ohms/25W resistor to 12V switched (terminal15) to avoid DME error storing.
For more detailed instructions, please follow the link: modBMW.com/mod