Correcting the Lotus Elise S1 STACK Coolant Temp Design Fault!
EVERY Lotus Elise S1 has the same design fault when it comes to the STACK coolant temp display. All owners know that the displayed value isn’t reliable as it seems to randomly jump from one value to another, causing false alarms in the face of the driver.
Only few know why this happens, so we will shed some light onto this and provide guidance how to correct it.
Time to modify
On the left picture you can see how the blue coolant temp sensor is wired to the STACK instrument. It is a single pole sensor which uses the engine and chassis as return line, while the STACK is connected from its connector pin A2 directly to the negative pole of the battery. The problem is that whenenver a current is rushing in or out the battery (Lights on, Cooling Fan on etc.) it causes a (small) voltage drop across the whole chassis connection.
From the picture it can easily be seen that this voltage drop is directly added to the voltage provided by the coolant temp sensor and measured by the STACK. It is high enough to falsify the reading of the STACK easily and this is a significant design fault.
The only thing you can do to correct it, is to cut the ground cable of the STACK at the connector pin A2 and run a separate cable from the STACK to the chassis earth point in the back of the car near the ECU.
This reduces the problem significantly!
