Temperature gauge anxiety?

I will give my recent experiences:
Since putting my car back on the road again, the first journey was from RATS (checkout & MOT, etc) to Sussex. All went well. Since then I flushed the cooling system again, re-filled with anti-freeze & bled system fully.
Several times the temperature gauge went very high - up to the red section, then returned to normal 90 degrees. There was nothing abnormal that made me think the car was overheating, nor any loss of coolant. All components in the cooling system were in good condition. Then the gauge went haywire sometimes up to full off the end of the red scale.
I purchased an infra-red thermometer (Maplin, price reduced to £20, so a very affordable tool with many other uses).
I tested the thermostat again and validated thermometer readings. (IR thermometers are good with dull, dark surfaces, not shiny metal surfaces) - all good. I checked hose surface temperatures, thermostat housing, radiator end caps. All areas were at normal levels. Therefore no immediate danger to the health of the car.
I took off the instrument fascia + under steering column and wiggled & cleaned all terminals in all connectors. The water gauge & oil pressure too could be made to read whatever from zero to max and in between. The disturbances had upset the gauge readings of course. [10 way single row vertical connector to water/oil gauges was main culprit in the case of my car].
By cleaning and tightening each terminal, testing the resistance across each one, I got sensible & consistent readings again. Also the rev counter decided to work again.
Since then a combination of "spirited driving" and sitting in traffic has failed to lift the temperature gauge above about 95 degrees.
The point of all this to note is that minor resistance increases across terminals due to corrosion over decades can lead to increased readings especially water temperature. I noted all sorts of anxiety posted in the forum about duff or inconsistent instruments. This is one explanation & a result (So far, don't tempt fate!).

[mettersl]

An inspiring message, thanks...looking forward to getting to this stage with mine...I think, although I'd prefer it all to just work..

Mine used to do it, caused a few brown trouser moments.......long pins on the temp/oil pressure/oil temp board go dry, if it starts doing it again just give 'em a flick over with the iron and solder.
I think 'cos the pins are so long with the connector hanging off them they crack ever so finely, hence high resistance, give the binnacle a whack and it drops back to normal........repeat......

[BIG_MVS]

give the binnacle a whack and it drops back to normal........repeat......

JohnC won't like that! He's told me off several times for that advice. Although it does work....

It works but you must stick you're tongue out when you doing it ,if no joy,stick it out further

I think 'cos the pins are so long with the connector hanging off them they crack ever so finely, hence high resistance, give the binnacle a whack and it drops back to normal........repeat......

Sorry for the delay in responding to this ..... just got back from my hols.
Just be careful about this.
The original fault reported was of the temperature gauge reading high. If this should happen, it will never be a connection or pin going high resistance.
With any of these "one wire sensors" .... with the body of the sensor being screwed into the earth ... being engine or body of the car, The gauge reading can only go DOWN if there is a high resistance anywhere in its circuit ....... Never up.
The only other condition that I can think of if it not the actual sensor or .... in this case .... the coolant temperature actually going high, is that there is an intermittent short to earth in the wiring possibly due to a breakdown in the insulation somewhere between the gauge and the sensor.
I hope this helps.

John

Sensor on turbo is two wire John,does this make a difference?

Sensor on turbo is two wire John,does this make a difference?

Hi Lee,
In answer to above .... No it does not. One of the wires from the sensor goes to operate the coolant temperature gauge, and the other wire operates the coolant high temperature warning light.
It is similar to the older type two pin oil pressure / light sensor unit which does the same ..... big spade, light , small spade, oil pressure gauge.
And this is the same for the Atmo as well.