What difference does coolant temperature make?
Discussion
How does the engine use the information from the coolant temperature sensor to change things?
I ask because, messing about on my old Jetronic equipped Merc, I've put a resistor in place of the coolant temp sensor to make the computer think it's about 65 degrees celsius. Not that different from the ~80-85 it runs at in normal driving so you wouldn't imagine it would make a difference.
However in truth this wildly changes the driving characteristics of the engine. It particularly improves low-down torque and makes it behave rather jerkily as you come on/off the throttle.
How can such a seemingly small change make such a difference? Does the disparity between an 85 degree engine and a 65 degree temperature reading make it wildly out?? Even when the engine is 65 degrees it doesn't seem to drive as normal so I've probably put the resistor in wrong!
I ask because, messing about on my old Jetronic equipped Merc, I've put a resistor in place of the coolant temp sensor to make the computer think it's about 65 degrees celsius. Not that different from the ~80-85 it runs at in normal driving so you wouldn't imagine it would make a difference.
However in truth this wildly changes the driving characteristics of the engine. It particularly improves low-down torque and makes it behave rather jerkily as you come on/off the throttle.
How can such a seemingly small change make such a difference? Does the disparity between an 85 degree engine and a 65 degree temperature reading make it wildly out?? Even when the engine is 65 degrees it doesn't seem to drive as normal so I've probably put the resistor in wrong!
When it's cooler the engine would normally run richer. When it's hot, being richer would be great for throttle response, not make much difference to peak power, but raise the fuel consumption.
If the engine really is cold, it needs the extra fuel because it's harder to get the petrol to evaporate and mix with the air, so some of it ends up going straight through the engine unburned. In that respect, rich and hot is very different to rich and cold.
If the engine really is cold, it needs the extra fuel because it's harder to get the petrol to evaporate and mix with the air, so some of it ends up going straight through the engine unburned. In that respect, rich and hot is very different to rich and cold.
Edited by GreenV8S on Tuesday 11th November 22:54
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