should be controlled to boil at as shown this routine at step 2001 determines if the engine is running or not this of course may be carried out by sampling the output of the engine speed sensor 640 by way of example if the answer to this enquiry shows that the engine is not running then at step 2002 the power to the entire system is terminated however if the engine is running then at step 2003 input data such as the pulse width and frequency of a fuel injection signal if available and or a engine speed signal and an induction pressure signal are read and a determination made as to which mode of operation the vehicle engine is currently undergoing for example by comparing the sampled engine speed with the induction vacuum or alternatively the fuel injection frequency with the pulse width of the same signal it can be determined which of the load zones shown in fig5 the engine is operating in at step 2004 the appropriate temperature for the instant mode of operation is determiend and set in ram although not specifically shown in fig1 it will be of course appreciated that the control circuit 246 includes a microprocessor similar to that shown in fig7 which can execute programs of the nature depicted in the flow charts of fig1 to 17 fig1 shows in detail the warm up control routine step 1001 of fig1 as shown subject to the start of this program valves i and ii and iii are conditioned as shown under these conditions atmospheric pressure is supplied to the second and third chambers of the reservoir unit viz the control valve assume a condition.