Why does an 82 degree thermostat vary..........?

[sprint95m]

A theoretical question, if I may.......

On a slant four Dolomite,
Why is an 82 degree thermostat influenced by the outside ambient temperature resulting in a variation
of the temperature of a coolant?


I have tried an 88 degree thermostat in place of an 82 degree one and find that it maintains a steady temperature
(at halfway on the gauge) all year round, whereas
with an 82 thermostat it would be at half during the summer but only read between 1/4 and 1/3 during the winter months?

This fluctuation occurred on both a Sprint and an 1850. The type of cooling system used made no difference, that is to say
it was present on the standard thermo-syphon type with a belt driven cooling fan and on the (Saab influenced) header tank
system (with an thermo-switch controlled electric fan) I currently employ.

I have also eliminated the following as possibilities
radiator (going from standard to Saab 9-3 made no difference)
coolant ( " " water based or Evans waterless " " " )
fan type
heater supply (inlet manifold or cylinder head makes no difference)


The reason I decided to try the 88 degree thermostat in place of the normally recommended 82 version, was the Saab
used the 88 and, also looking at the specification for a 1972 slant four I found that the 88 degree one was originally fitted!


Any ideas?
thanks,


Ian

[dave comer]

Seems to me that the 82 opens earlier and that during the winter or colder weather, you would be suffering from over cooling. How accurate is the temp sender and gauge?

[tonybsa]

Now I have sorted my rad out,mine ALWAYS runs between a 1/4 and a 1/3,even when flogging it at speed,except when sat stationary in traffic when it reads 1/2,where the fan cuts in.I use an 82 degree stat,and the fan is set to come on at 90.
A very long term Sprint owner I know told me that between a 1/4 and 1/3 is where you want it,and if it goes to the mark after the 1/2,pull over and switch off,and allow to cool down or it will lunch the head gasket.

[Edin Dundee]

I have a nos temperature sender, it reads lower than the Rimmer option and seems less sensitive.
On a hot day I expect the gauge to show half-way after an 80mph run down the motorway then stop-start traffic in Edinburgh. If it gets above that I know there's a problem.
The Rimmer option showed half-way on the gauge in stop-start traffic without the fast run, but I was warned about this by the much missed JPB.
That's with an 82 degree thermostat.