Temp Gauge Sudden Jump!!?

Hi, i know this has been covered but after being so intermittent ie 3 times a year, it has now happend 3 times in 3 days
Basically, cruising around (no puns please) & the temp gauge suddenly jumps up to RED....not gradual..just jumps...fans come on, no steam etc....pull over & switch off the engine...start her up again 20 secs later & the temp gauge is fine ie halfway

Now, if it was overheating/problem the gauge would not have been sitting back to normal after 20secs...it would still be RED..

I know a few people have had the same problem but has anyone actually got to the bottom of it

Cheers.......

not much help on a hot day but heater blowing cold not hot is a good diagnostic of cooling system issue ,temp switch or wiring to it

jamesmartin said:

not much help on a hot day but heater blowing cold not hot is a good diagnostic of cooling system issue ,temp switch or wiring to it

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Totally agree, last few times/days it has been warm days....its just a matter of what is causing the gauge to do this as i do not think it is overheating as the gauge would creep up & not just 'jump' & subsequently be normal after turning the engine off/on after 20 secs...

So....sensor/wiring would seem logical.....

Could be an airlock in the coolant - what engine is it??

What's the coolant level like?

td4van said:

Could be an airlock in the coolant - what engine is it??

What's the coolant level like?

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Hi, its the 1.8 engine.....runs sweet as a dream, coolant is at the correct level/never alters & seems to circulate as you can see the feedback from the small tube in the reservoir...

Thanks

It's more likely a dodgy connection on the CTS or its wiring between the CTS and the ECU, or the CTS is on it's way out.

Nodge68 said:

It's more likely a dodgy connection on the CTS or its wiring between the CTS and the ECU, or the CTS is on it's way out.

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Sorry for my ignorance.....CTS....coolant temp sensor?

Thanks to all......

The fan is controlled by the ecu, if the temp gauge hits the red then the fan will run, regardless of engine temp, as happened on my TD4 when a wire got chafed and earthed out, it should also run for a few minutes after engine shut down.

BigRog said:

The fan is controlled by the ecu, if the temp gauge hits the red then the fan will run, regardless of engine temp, as happened on my TD4 when a wire got chafed and earthed out, it should also run for a few minutes after engine shut down.

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Hi, thats good to know as the fans do run (bloody noisy buggers) when this happens & after i stop.....they dont come on again afterwards.....will have a look/trace the wiring today & possibly order a temp sensor as not too expensive....

myths63 said:

Sorry for my ignorance.....CTS....coolant temp sensor?

Thanks to all......

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You got it
The fan is running because the ECU is losing temperature information from Coolant Temperature Sensor or CTS. This causes the ECU to substitute the actual temperature for a safe value of 120ºC. This puts the fan on and register hot on the guage.
It sounds like a dodgy connection to me.

Nodge68 said:

You got it
The fan is running because the ECU is losing temperature information from Coolant Temperature Sensor or CTS. This causes the ECU to substitute the actual temperature for a safe value of 120ºC. This puts the fan on and register hot on the guage.
It sounds like a dodgy connection to me.

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Cheers Nodge......will order a new one today, thanks to everybody as always

myths63 said:

Cheers Nodge......will order a new one today, thanks to everybody as always

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There are no guarantees it's actually the CTS that has failed. They can suffer a bad connection which will give the same symptoms.