Re: Temperature gauges

[Mike Wattam <MikeWattam@domain.elided>]

Hi John

Well, some very good points.

The only thing that really matters, is the temperature the water comes out
of the engine.  You are absolutley right when you say the problem has
happened before the temperature guage can pick it up - Even without this,
problems usually still occur and have their consequence before the
temperature change registers on the guage.  This is commonplace on cars and
commercial vehicles, it is not peculiar to the Stag at all.

On the Stag, the standard sensor is not even at the hottest part of the
engine anyway, and is also deep in metal which makes it even slower to
react.   And on the Stag this is made even worse as it uses the voltage
stabiliser to 'damp' the guages out.  Thus, it is very easy for the engine
to be completely cooked before the guage will tell you anything.  In
extreme cases where the water leaves the engine entirely, the pistons can
seize ot the cylinder block while the temperature guage reads lower!

We tried using it aginst the head, cylinder block area etc., but the
problem of speed of heat transfer is the over-riding consideration. 
Ideally, the sensor should be in the water flow, but as we would not wish
to impede it in any way, this was not found to be desireable and it
actually gives good results attached to the outside of the hose with the
fastest reaction to water temperature change.

The temperature setting of the sensor is set to allow the thermostat to be
fully open plus a small margin of tolerance, less the maount of natural
cooling from passing air.  Therfore with a normal-running Stag engine it
should never come on, and with one that overheats slightly very seldom. 
Thus it may be triggered by a traffic jam when the water and air
circulation through the radiator is insuufficient to carry away the heat,
or by high speed driving when the radiator capacity is insufficient to keep
optimal water temperature.  We want to know these things, and that is all. 
Thus a Stag which overheats often, is going to be a bit of a problem.  The
designer insisted on incorporating a manual on-off switch against my
judgement, so if the noise/light is literally a pain it can be switched
off.

We have tried to make it as good as possible within a tight budget.  At the
end of the day it is just a crude sentry which gives at least some warning,
and is in many ways much better than a temperature guage.

Hope this helps.

Mike Wattam
Triumph Stag Register