Next Gen Cooling system

Written 07/06/2010:

Made some electrical changes, some outputs were swapped around. Lot of data has been collected with different pump speeds.

Here is one measurement from 20 min drive this morning. It has two pump speeds, 50% and 100%. Upper graph is water pressure and lower is the engine temperature.

Engine temperature is measured from the engine temp gauge sensor. Interesting in the upper graph is how water pressure fluctuates before thermostat opens.

At the moment it looks like 50% speed is enough to keep the engine cool at low loads.

Electrical thermostat and water pump for 540i were ordered, should be here this week. Water pump will be modified and thermostat will be replaced with electrically controlled thermostat.

 

Written 06/28/2010:

Electric Water pump is now installed and is being tuned. System has following parts:

• Johnson CM90 coolant pump, located where the air conditioning compressor usually is. Pump Capacity 65l/min (17.2GPM), current draw about 9A at full speed.

• Modified OEM water pump, impeller removed and some inputs blocked

• Meas-Spec MSP300 series pressure sensor to measure the coolant pressure

• Coolant pump controller. Mitsubishi Fan controller, part number: 1355A143

 

Electrical schematic:


Coolant pump controller takes the voltage from the same relay as the ignition coils.

Idea here is that if the ignition circuit fails, coolant pump can fail too since engine doesn’t run. Coolant pump is connected directly to the controller, which is a Fan controller from Mitsubishi Outlander.

It has internal pull-up resistor, short circuit protection and over current protection built-in. SM4 can control the unit directly.

Coolant pump speed is controlled by SM4 Swf PWM3 output and uses GPC10 table. Physical output is Output 5. Table axis are Coolant temp and RPM, inhibit functions are not used. Following video shows how pump flow varies by changing the table values:

As you can see, I don’t use any antifreeze since freezing is not an issue here. Water is the best for cooling together with corrosion inhibitor. 
Thermostat is still in place since I want to make sure system works before I modify the whole circuit.
One thing I’m going to try is to remove the thermostat all together and vary the pump speed directly using PID method.

If this doesn’t work out, next trial is to remove the old thermostat and replace it with an electric thermostat where the opening temperature can be controlled with SM4 between 80 – 103 degrees C. 

This way I could run higher temps (100 degrees) at low load and reduce the temps (85 degrees) while on full load to prevent knocking. Opening temperature would be controlled by one of the SM4 outputs.

One problem with this might be the speed how fast the temperature will drop.
One additional thing to try is to increase the coolant system pressure. Higher coolant pressure should increase the cooling and is important in order to reduce cavitation. Before I can do that I might have to change the radiator to a different one, I don’t think this old one will last more than 1.4Bar pressure.
Preliminary tests show that pump is able to keep the temps at 85 degrees at idle without any issues.One idea was to leave the pump running to reduce the temps after engine has been shut down, but temperature decrease is slow, about 1 degree C / 1 minute. I don't think this makes sense now since I would have to leave the pump on for a long time and battery might drain empty.

Modified "water pump" with pressure sensor and heater return hose splitter.

Written 11/24/2009:

Got the pump now, it is Johnson C090 water circulating pump made in Sweden. It was selected since it is well known and used widely in drag racing. Another positive thing is that current draw will be low.

 

Written 10/06/2009:

One of the problems currently is that oil heats up quite slowly. Oil thermostat doesn't even open after 25 minutes of driving. One way to make engine faster is to turn off the water pump so that water doesn't. But, how to disable the pump since it is driven by the belt?

Idea is to replace the belt driven pump with electric pump. Since the pump is used to control the coolant flow, thermostat can be removed. Pump would be controlled by Autronic ECU.

Below is a diagram of the OEM M3 cooling system showing the coolant circulation.

 

Here are some FAQ's from Davies,Craig page about cooling systems and electric water pumps