Calculated Load

And

The Electrics

As most people will know, in addition to providing power to drive the car forwards, the engine must also provide electrical energy (by driving the alternator) to both provide the ECU with the necessary power, and of course any other circuits that are active.

When Kermit’s donk is idling - once warmed up - the idle Calculated Load figure is approximately 24% with all electrical circuits switched off. This table below shows how turning on individual circuits increases the loading on the engine, and also demonstrates how much harder the engine is having to work at idle to provide the necessary power.

Idle Load Increase	Idle Consumption Increase	Detail
+1%	+4%	Interior ventilation fan, position one.
+2%	+8%	Interior ventilation fan, position two.
+4%	+16%	Interior ventilation fan, position three.
+7%	+28%	Interior ventilation fan, position four.
+3%	+12%	Electric window.
+0%	+0%	Electric mirror.
+15%	+60%	Air conditioning compressor, interior ventilation fan at position one, cooling fan at slow speed.
+6%	+24%	Heated rear windscreen and mirrors.
+10%	+40%	Heated front windscreen.
+1%	+4%	Parking lights.
+5%	+20%	Dipped headlights.
+10%	+40%	Dipped headlights and main beam.
+4%	+16%	Cooling fan, slow speed.
+2%	+8%	Footbrake (pressed reasonably firmly).

Note that the air conditioning system’s effects are included in the above table for academic reference only.

The above increases are only applicable when the engine is up to normal temperature, idling, and only when turning on one circuit or perhaps two of the lower current circuits. Switching the interior ventilation fan to setting four, switching on “Quickclear” and holding the footbrake down does not increase the loading from 25% to 50% - the alternator is unable to supply the necessary current and the loading remains at approximately 50%, but the fan speed is slower and the bulbs glow rather dimmer.

Once on the move the above increases are no longer applicable because of the computation required to display the Calculated Load figure. A Calculated Load of 50% at 850 rpm is not the same amount of work done as a Calculated Load at 2,500 rpm.

The above table illustrates another reason why idling the engine with a number of electrical circuits switched on is detrimental to fuel consumption. When combined with a cold engine, one can see how running “QuickClear” (the heated front windscreen), the heated rear windscreen, and the lights, can increase fuel consumption when idling.