[Mgs] The Continuing Quest to Cool my MGA

[Paul Hunt]

The funny thing is, with some thermostats that is exactly what happens! 
Thermostats for certain heating systems have a heating element inside them 
which causes the thermostat to switch off the boiler (and disconnect power 
to the thermostat heater) even though the room (or what ever) isn't up to 
temperature yet.  After a few moments the thermostat cuts in again and so 
on, cycling the boiler on and off, until the room gets up to the selected 
temperature.  As it does so the off periods gradually get longer and the on 
periods shorter.  The purpose of this is so that you don't get localised hot 
spots but the whole house heats up gradually and relatively evenly.  With 
these stats turning it way up *does* heat the house up quicker, as the 'on' 
periods are longer if not continuous.

The even funnier thing is that this is also how the voltage regulator on 
dynamo-equipped cars works, except the on and off periods are measured in 
fractions (thousandths) of a second, when it replaces the charge taken by 
the starter.

But as far as thermostats in a 'getting hotter than normal' situation goes, 
I'm right with you.  While the cooling capacity of the radiator exceeds the 
heat output of the engine, the thermostat will be opening and closing to 
some extent, or not fully open, and the temp gauge will be about N or about 
the temperature of the stat as appropriate.  As the heat output exceeds the 
cooling capacity the temp gauge will start to read above the 'normal' point, 
higher and higher as the heat output exceeds the cooling capacity more and 
more.  When comparing increasing speeds on the flat as the heat output goes 
up the cooling capacity also increases to somewhat balance it out, by the 
higher speed through the air.  Where the effect is most noticeable is when 
changing from cruising on the flat to slogging up a hill, probably at a 
*slower* speed i.e. less cooling but with much more heat output.  But even 
here the system is partially self-regulating, as when you increase the 
temperature of the coolant through a given cooling system it actually gets 
more efficient as the temperature differential between coolant and cooling 
medium i.e. the air is greater and the air will take more heat out of the 
coolant.

The paradox is that fitting a *hotter* stat (as I think your old car chap 
recommended) is actually the *wrong* way to go, just imagine the effect of 
fitting a 250F stat (if you could get one and were foolish enough to fit 
it).

PaulH.

----- Original Message ----- 
> ... change my thermostat to 190 instead of the 170 !!  This is akin to
> people turning the thermostat up (beyond the required temp) in houses
> when they wish the house to get warmer quicker!!!