Thread: Coolant alarms

Originally Posted by Urban Panzer

Yeah seen that kit and can get it over here to, I like the simplicity of the screw in sensor, its just after reading the detailed post on here ref coolant alarms, it seems the top hose will still be full of coolant even when its loosing it "other" places, so im wondering how much you have to loose before it senses it.

U.P, interesting question.

As we know, the screw-in hose sensor, is fitted to hose (5). This is the top hose where coolant flows from the engine to the top of the radiator. There are two smaller hoses which flow coolant out of the top hose to the heater inlet pipe (4) and thermostat housing (13) respectively. The expansion tank (17) has coolant flowing from it through the heater/expansion tank return hose (16) to the coolant pump feed pipe (9). Coolant from the fuel cooler (22) also flows through the heater/expansion tank return hose (16) to the coolant pump feed pipe (9).

Ignoring the other smaller pipes, would I be correct in saying, the expansion tank and top hose would both be ideal locations for a sensor detecting a drop in water level?

If you think about it, the top hose may be a more suitable location as there is less water stored in the pipe itself and it has two pipes which can drain coolant out, thus creating an air lock around the sensor, which is fitted at the highest point of the top hose. Whereas the expansion tank may in fact drain slower as there is more stored coolant.

Any other interpretations or tests people have done?

Hi All

Just a bit of perspective from a manufacturers viewpoint.

The land Rover header tanks (expansion) have a horrible reputation for
cracking so it never made sense to me to start drilling holes in them for
low coolant sensors.

That leaves the thermostat housing, the top hose and the radiator top tank.

The early V8, and 200/300 tdi have an existing bleed plug in the top of
the radiator tanks which is an ideal position for a sensor.
So I manufactured sensors for them.
We ran a laser level through the engine bay of a 300tdi Defender and established that the sensor is at the same height as the recommended coolant level in the header tank.

The 200/300 td1 also have the same plug in the thermostat housing
but there is always an air pocket underneath it which takes a while to fill on start up and needs an unacceptably long alarm delay or a very long sensor to reach the coolant, so the radiator makes more sense.

The later V8 & Td5 have no bleed plugs in the radiators, which have
plastic tanks which would require drilling and the self expanding type of sensor fitting.
These type of rubber bung sensors are unreliable and the size of hole
needed to be drilled in the tank could compromise its integrity.
In fact many radiator repairers are now refusing to drill holes or fit sensors through plastic radiator tanks.

So.. I manufactured sensors to simply replace the bleed screws in the top
radiator hoses.
These screws are effectivley at the highest point in the system so air can be bled out and are a good place to position sensors.

Just one point someone else made regarding the TM-2 ( Which I am an agent for & also convert to dual sensor low coolant / high temp units)

Never fit the sensor to the thermostat housing, as if coolant is suddenly lost, the alluminium will rapidly cool and not heat up again untill after heat soaks into it from the already overheated cylinder head.
This information came from a man who cooked his Land Rover engine with the heat sensor fitted in that position.
It gives a really close to coolant reading but is not reliable as far as engine protection is concerned.


Davy