Disco 1 A little projectipoos....... (300TDi Low water Alarm/fan control)

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The Mad Hat Man

The Mad Hat Man

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LZIR Despatch Agent
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Having got a 300TDi Disco, one is always concerned about overheating issues as the 300TDi is notorious for cooking the head if the water level drops slightly. This is due to the thermostat housing being the highest point in the engine and the water pump being very high. It doesnt take much coolant loss for te pump to suffer from cavitation and the engine to overheat. :(.

Many moons ago (about 10 years ago) some fella produced a magic box to give warning of low water level and, hopefully, enable the owner to stop before it was too late. Unfortunately this system appears to have disappeared from the annals of Landrover websites. So I thought I would have a go!!!!:eek:
Being blessed with aircon on this beast, I have a couple of electric fans mounted in the front of the radiator, so these were the obvious choice to use.
The criteria that the system had to comply with is as follows :-
To be fail-safe - ie if the sensor or sensor wiring failed, then the warning would still work.
To show that the system was functioning correctly on power up.
To automatically show low water level
To allow manual switch-on of the fans when required.
To automatically switch the fans on when the coolant reaches a pre-determined temperature.
To still work as "normal" air conditioning fans when fault conditions are not present.

To this end I had to buy the following extra components (as well as the controller box)
manual fan switch (with warning light) (I had an old Kenlowe switch)
Range Rover low water sensor cap (PRC7925)
Thormostat housing elbow (ERR3738)
Overheat sensor (PRC3359)
P5 pin relay
various wires, connectors and sleeving

Here are a few pics and videos of the final system.

Low Water Sensor and magic box
IMG_4536.JPG


Additional Fan Control Relay
IMG_4537.JPG




Overheat sensor in Thermostat elbow
IMG_4538.JPG


Power and Ground taken from Fuel pump
IMG_4539.JPG


Power up sequence - Low coolant warning light


Power up sequence on fan control light and manual override


Power on sequence and overheat overide (simulated)


"Magic box" is available in 3 options :-
1) low water level warning only.
2) low water level and fan control.
3) low water level warning, fan control and overheat control.

From £25. NB. Does not include external items such as low water sensor, fan control relay or overheat switch.
 
Last edited:
The Mad Hat Man said:
Having got a 300TDi Disco, one is always concerned about overheating issues as the 300TDi is notorious for cooking the head if the water level drops slightly. This is due to the thermostat housing being the highest point in the engine and the water pump being very high. It doesnt take much coolant loss for te pump to suffer from cavitation and the engine to overheat. :(.

Many moons ago (about 10 years ago) some fella produced a magic box to give warning of low water level and, hopefully, enable the owner to stop before it was too late. Unfortunately this system appears to have disappeared from the annals of Landrover websites. So I thought I would have a go!!!!:eek:
Being blessed with aircon on this beast, I have a couple of electric fans mounted in the front of the radiator, so these were the obvious choice to use.
The criteria that the system had to comply with is as follows :-
To be fail-safe - ie if the sensor or sensor wiring failed, then the warning would still work.
To show that the system was functioning correctly on power up.
To automatically show low water level
To allow manual switch-on of the fans when required.
To automatically switch the fans on when the coolant reaches a pre-determined temperature.
To still work as "normal" air conditioning fans when fault conditions are not present.

To this end I had to buy the following extra components (as well as the controller box)
manual fan switch (with warning light) (I had an old Kenlowe switch)
Range Rover low water sensor cap (PRC7925)
Thormostat housing elbow (ERR3738)
Overheat sensor (PRC3359)
P5 pin relay
various wires, connectors and sleeving

Here are a few pics and videos of the final system.

Low Water Sensor and magic box
View attachment 104041

Additional Fan Control Relay
View attachment 104042



Overheat sensor in Thermostat elbow
View attachment 104043

Power and Ground taken from Fuel pump
View attachment 104044

Power up sequence - Low coolant warning light


Power up sequence on fan control light and manual override


Power on sequence and overheat overide (simulated)


"Magic box" is available in 3 options :-
1) low water level warning only.
2) low water level and fan control.
3) low water level warning, fan control and overheat control.

From £25. NB. Does not include external items such as low water sensor, fan control relay or overheat switch.
Click to expand...


Going to do something similar (but simpler with out thefor my dad on his disco 200tdi - couple of questions mate.

Did the RR cap fit your header tank without any adaptation? Do you know if it will fit a 200tdi header tank?

What output does the low water sensor produce? is it essentially a open circuit that 'closes' the switch when low? I think I'll just run a simple buzzer in series with the switch taking power off the FIP pump
 
payydg said:
Going to do something similar (but simpler with out thefor my dad on his disco 200tdi - couple of questions mate.

Did the RR cap fit your header tank without any adaptation? Do you know if it will fit a 200tdi header tank? Yes and yes.

What output does the low water sensor produce? is it essentially a open circuit that 'closes' the switch when low? I think I'll just run a simple buzzer in series with the switch taking power off the FIP pump
Not as simple as that. The water level sensor is a <>600ohm variable resistor, not a simple switch, so it needs an electronic circuit to trigger a relay
Click to expand...

Use the gearbox overheat lamp as the overheat warning.
I used the FIP pump for power too.
 
I can see all pics on this page. Way back, you made a thread on this - I asked you about it as wanted to do it but no pics were on there. This supersedes that thread
 
payydg said:
Ah I see - do you need a particular relays to switch the warning lamp on at a certain resistance? You can probably tell I'm not a natural electrician?
Click to expand...
YEs.... and no. Yes, you will need a relay and No... not just a relay. you need an electronic circuit that takes the variable signal from the water level sensor and which will then switch a relay "on".

If you are intending to use the warning lamp to show the overheating from the thermostat housing switch, then you just need the switch to bridge the two wires from the warning lamp cable. NO EXTRA POWER IS REQUIRED
 
The Mad Hat Man said:
YEs.... and no. Yes, you will need a relay and No... not just a relay. you need an electronic circuit that takes the variable signal from the water level sensor and which will then switch a relay "on".

If you are intending to use the warning lamp to show the overheating from the thermostat housing switch, then you just need the switch to bridge the two wires from the warning lamp cable. NO EXTRA POWER IS REQUIRED
Click to expand...

I’m just going to make a more simple version of yours with a aftermarket red lamp - the landy doesn’t have a gear box over heating alarm.

I’m struggling to get my head round how you’ve set it up to take the variable signal and get that to switch the relay on? You couldn’t point me in the right direction.
 
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