Temperature light anomaly

[Jocko]

I thought I had a problem this morning. I get the car out of the garage, drive the same route, in the same light traffic and at the same spot on my journey the blue water temperature indicator goes out. It varies by no more than 40 - 50 yards depending on outside temperature, taking a bit more on a frosty morning then on a normal morning.
This morning it didn't go out, and after about a quarter of a mile I had just started to say to my wife, "I think I have an issue here", then out it finally went.
It is a really mild morning here, currently about 8°C, and the car has been in the garage, overnight, as usual. Obviously, as it is still pitch black, I haven't checked anything, but it was strange that it took so long to go out.

[sparky Paul]

Sounds like one to 'let it develop'.

Could just be a sticky thermostat, or disintegrating gasket?

[Jocko]

Set up my ScanGauge to display temperature. When I used it later in day it performed as usual and the blue light went out at its usual 54°C. I checked radiator level and everything was spot on in that department.
The old style thermostats used to fail in the open position, which caused slow warm up, but the newer wax pellet variety fail shut, causing overheating.
I'll see what happens tomorrow morning when I repeat today's circumstances. At least this time I can see what the temperature itself is doing.

[Jocko]

Light went out at the usual place at 54°C. By the time I got to the point where it went out yesterday, however,  the temperature had only reached 58°C, so hardly a big difference. Perhaps the thermostat had not closed completely after Monday's last run of the day. Don't think I'll let it spoil my Christmas (even though I will have a lot of driving to do on the big day).

[sparky Paul]

The old style thermostats used to fail in the open position, which caused slow warm up, but the newer wax pellet variety fail shut, causing overheating.

Not always Jocko, I've replaced a couple that got tired and became leaky when shut.

Don't think I'll let it spoil my Christmas

Nor would I!

[Jocko]

Think I have solved my problem. As I have said elsewhere, I do not use the heater on my short morning commute, believing that to do slow slows the engine warm up and impacts fuel economy.
When we are out in the car my job is the driving and Mrs Jocko controls the heater and changes the CDs. I normally drive with my jacket on and, being a man, my body copes with the vagaries of temperature. My wife on the other hand, along with women in general, need the temperature controlled within that 0.5°C their species requires.
What had happened was the heater had been left on and the fan was at setting one. I tried doing that this morning and the temperature took that extra quarter of a mile to reach 54°C and the blue light to go out.
Just shows that my theory about it slowing the engine warm up was correct!

[sparky Paul]

Just shows that my theory about it slowing the engine warm up was correct!

Indeed it is, extracting heat from the heater matrix by turning up the blower has the same effect as opening the thermostat to the radiator. Mystery solved.