Originally posted by andyrennison ;
Once its open it can do nop nore,
Correct

so if the water returning from the rad is the temperature that the stat allows out,
Reliant vehicles normally run best with an 88 degree thermostat and as OAB SAYS
The purpose of the wax stat is to allow the engine to get to an optimal working temperature before allowing the coolant to go to the rad to cool down.
The water from the open stat will be a
minimum of 88 degrees when it flows from the head to the TOP of the rad .
It then drops /is sucked downwards through the rad getting cooled on the way down by the mechanical fan and the air coming in through the front of the car to the front of the rad
when the vehicle is moving The temperature in the engine bay on the 3 wheelers is quite high and with the mechanical fan on all the time this is normally enough to stop overheating when the vehicle is stationary for long periods of time in traffic jams .
Note that
all Reliant engines should be run with antifreeze at the correct mix all year round { Not called Summer Coolant for nothing

}.
The water
going back into the engine via the bottom hose is cooler than that going in at the top .
On an open trike you have a
slightly different scenario .
{
1 } You do not have the engine enclosed in a fibreglass box therefore ,
when moving , you get some air cooling on the engine as well as via the rad
{
2 } For cosmetic { Not wanting to have to build a guard round the fan so that unattended morons and kids do not get their fingers broken

} or slight power gain the mechanical fan is removed
An electric fan , if fitted , has no brains and needs to be told when to come on and off .
Picture the scenario ;
The temp from the engine to the top of the rad is a minimum 88 degrees after the thermostat opens .
The temp at the bottom of the rad is a less than 88 degrees due to being cooled by the air flowing through the rad .
If the temperature at the bottom of the rad rises that means that the temp at the top is obviously much higher .
So if you put the electric fan sensor in the bottom hose and set it to come on at a lower temp than 88 degrees then the fan will kick in .
After warming up fully and after a run , if you use one of the following to check the temp at the top hose and at the bottom hose ,you will know what temp to set the sender at { Which I assume would be set at normally a degree or so above the normal temp in the bottom hose ?}
http://www.ebay.co.uk/itm/NEW-Non-Contact-Digital-IR-Infrared-Digital-Thermometer-With-Laser-/180906684657?pt=UK_BOI_Electrical_Test_Measurement_Equipment_ET&hash=item2a1ee0f0f1.
If someone does buy one of the above digital thermometers I would be interested to know the temp difference between the water in the top and bottom hoses as I do not have a clue

.
.