Other S80 Problem: Temp gauge shot up

[Scotty68]

Hi there, the temp gauge on my s80 shot up last night, water in expansion tank fine, heater blowing warm air ,not hot ( but had only driven for 15 mins) . Top rad hose warm ,bottom rad hose cold. Phoned RAC and got recovered home. Went out this morning ,turned the key ,gauge shot up . started the engine ,ran it for 15 mins no water in the oil, and top rad hose warm ,bottom cold. Any help would be appreciated

[D5meister]

Sounds like temp sensor is knackered or is the wire off it.

Somyimes the guages endstop if the sender wire is off, dunno which way round it is on these.

[Dancake]

Faulty coolant temperature sensor, faulty temperature gauge, faulty thermostat or a fault in the wiring/circuitry somewhere. See if you can get the codes read to see if any fault codes have been logged in relation to the cooling system. Think the gauge fails to safe, meaning the needle will go into the red if the gauge or temp sensor fails.

[cheshired5]

Originally Posted by Scotty68

water in expansion tank fine

Hopefully your mean coolant.
If you have just water in your system, that's bad news.
Coolant sensor testing takes minutes with diagnostics or a multimeter. Do you have either?

[oragex]

After 15 min I would expect the upper hose to be pretty hot, especially if you have the bigger engine, unless it's very cold outside. The stat might be stuck open.

As for the temp sensor, if in red on cold engine it's has perhaps shorted, as mentioned above