Date: Tue, 18 Feb 2003 10:45:09 +0000 From: Grunff <grunffnopsam.com> Subject: Re: heat question
Andy wrote: > Sounds to me like your sensor (thermostat) is on its way out and isn't > correctly picking up the temperature correctly. There are two sensors to be > aware of and both interact with each other from memory, to find a > balance/ensure correct reading. If one is damaged.... no big cost, probably > around £50 at a main dealer, cheaper if local garage. The thermostat and temperature gauge sensor are two totally different things, which don't interact with each other in any way (other than via the temperature of the coolant). The thermostat is a mechanical valve, which is operated by an expanging chamber filled with wax. It opens when hot, allowing coolant to flow through the radiator. The temperature sensor is a thermistor whose resistance varies with temperature, and this controls the level of the needle on the gauge. There is a third 'sensor'; the fan thermo switch. This is a bimetallic electrical switch which switched the radiator fan on when the coolant temperature exceeds a pereset value (82/87/92C). The OP's symptoms are characteristic of either a sticking thermostat or air in the coolant system. Both are easily rectified. > Also worth noting that thermostat/temp gauges are 'dampened basically for > drivers piece of mind so when an engine is at correct temperature, the gauge > is usually about half way - it would normally be nearer the top in reality, > but customers don't like to 'see' this as they worry too much. So they > regulate the view of the actual temp, hence why I think the > sensor/thermostat is at fault. As explained above, the sensor which feeds the temperature gauge and the thermostat are two separate things, and not related in any way. As for the damping, the gauge is damped, but damping prevents rapid fluctuations, rather than reducing the temperature. -- Grunff
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