Water Temperature Gauge

[AdamWilkes]

Agreed, 100 degrees is not actually the usual boiling point in a radiator (pressurised and/or impure water boils at a lot higher temperature). At 10psi above atmospheric pressure (well within reason in a car cooling system), the boiling temperature is 115 degrees centigrade, probably higher when the impurity (antifreeze) is allowed for.
I don't expect all water temperature gauges are built the same way, so a comparison on where the needle sits between two completely different gauges seems unreasonable. You need to know what the temperature really is, using a good accurate sensor/gauge, and then 'calibrate' your current gauge to suit - ie keep it, chuck it in the bin or buy a better one.

 

[Mike Cordeiro]

On the initial post, concern was shown about the needle "hovering around the top end of the gauge".
When I mentioned that on the VDO gauge the needle sits right in the middle, I was not impling that the needle must sit in the middle on any gauge,regardless of what it reads.
In most cars of this era the engine operating temperature is between 88 and 92 deg. Celsius. On the gauge in question that temperature range is past the halfway mark giving a false sense of "running hot". (I actually believe that it is reading just fine)
On the VDO gauge that temperature is right in the middle of the gauge.
I also fitted one of these gauges and it bothered me seeing the needle always past middle although reading correctly.
eventually I just bought a VDO unit and now sits halfway or just short of it.
I also found that, if the sensor is fitted to a radiator or heater pipe and the thermostat fails to open by the time the sensor picks it up it will be too late. The sensor will have to be on the water pump or on the engine itself.
It is very interesting learning and exchanging different views on all of this topic. Thank you guys.

 

[Sage103]

Not wishing to raise the temperature any further let me just add that I have ordered an external temperature sensor in order to confirm my conclusion that all must be well given that thermostat and radiator sensor appear to be working correctly. And let me just repeat that fitting the gauge sensor to the water pump is not an option on my car. But I am fairly happy with the top hose location as it allows the gauge to register the fact that the thermostat has opened within five minutes or a mile or so after startup. I am not worried about the thermostat suddenly closing thereafter but I would like to be aware of an increase in engine temperature due to adverse road conditions (such as Hardknott Pass in the Lakes or driving into or out of Edinburgh during the rush hour).

 

[Sage103]

Happy to report that infrared temp sensor failed to detect any meltdown condition in the top hose or radiator so I’m back to trawling my collection of OS maps for proving runs (for R4 and for GoPro) prior to an assault on the North Coast 500!