temperature gauge query

[ianh]

Hi all.
I have a 1985 500sl
I've noted my temp gauge sitting halfway between 80 and the next,unmarked,line (100 degrees?).
I can sometimes see the needle fluctuate, and rise or fall, though not always.
It moves around in that 'quarter'of the gauge, but doesn't go past the 100 degree line.
Whilst the engine was running, after a 60 mile journey,I removed the 'radiator'cap, and was able to remove it easily. I thought I would it would be under pressure and feel tight,but there was hardly any tightness at all.
My concern is - Should I be concerned?
Is it an airlock?
Is it the symptom of a failed thermostat?
If not, is it normal?
I assumed that the temp gauge would sit at 80, but I can't recall if it ever did!
when will the air con fan cut in?
Any and all advice welcome....

 

[LastMinute]

when will the air con fan cut in?

Depends on the setup, but for an old (= simple) system such as yours, it will be when the refrigerant temperature is too high - which should be (to an extent) independent of the coolant temperature.

 

[grober]

Hi all.
I have a 1985 500sl
I've noted my temp gauge sitting halfway between 80 and the next,unmarked,line (100 degrees?).
I can sometimes see the needle fluctuate, and rise or fall, though not always.
It moves around in that 'quarter'of the gauge, but doesn't go past the 100 degree line.
Whilst the engine was running, after a 60 mile journey,I removed the 'radiator'cap, and was able to remove it easily. I thought I would it would be under pressure and feel tight,but there was hardly any tightness at all.
My concern is - Should I be concerned?
Is it an airlock?
Is it the symptom of a failed thermostat?
If not, is it normal?
I assumed that the temp gauge would sit at 80, but I can't recall if it ever did!
when will the air con fan cut in?
Any and all advice welcome....

You need a new "radiator cap" for starters would be my guess. To bleed the cooling system you could try elevating the front of the car slightly so the radiator/header tank is the highest point in the system and add water squeezing the radiator hoses to help release any trapped air.

 

[recycled]

I do not think there is anything wrong. after a fast journey with cool air into the rad it will be quite easy to open.
Sit in traffic for an hour and see where the needle gets to