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False coolant overheating warnings


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Hi. I'm new to the forum so please bear with me. (Think I posted this in the wrong area first time round!)


I've got a weird problem with my daughters Fabia. For no apparent reason the temperature gauge will suddenly go from normal to max even though the engine is not overheating. At the same time both the red thermometer symbol and audible warning come on. Everything returns to normal when the engine is switched off and re-started. Our local garage haven't got a clue and have suggested we sell it and buy another car; not very helpful as we only bought it in July! Any suggestions as to what may be causing it?


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Take it to a better garage! a decent one should be able to diagnose the problem. I see you're in Southampton, JKM is a vw specialist based in Portsmouth and they are very good, they will probably be able to help you out

 

Andy

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Take it to a better garage! a decent one should be able to diagnose the problem. I see you're in Southampton, JKM is a vw specialist based in Portsmouth and they are very good, they will probably be able to help you out

 

Andy

Not a bad idea, but I'm trying to avoid multiple costly diagnostic visits that don't resolve the issue. No harm in giving them a call though.

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Are you sure it's the coolant temperature and not the level that's giving the false positive?

 

Either way, my first thoughts are to clean the metal sensor prongs in the level/expansion bottle by scraping them with a flat screwdriver when the engine is overnight cold, or replace it (about £15) if you can't see them.

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Are you sure it's the coolant temperature and not the level that's giving the false positive?

 

Either way, my first thoughts are to clean the metal sensor prongs in the level/expansion bottle by scraping them with a flat screwdriver when the engine is overnight cold, or replace it (about £15) if you can't see them.

OP says: "the temperature gauge will suddenly go from normal to max"

 

I would suggest replacing the coolant temperature sensor, cheap and easy.

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OP says: "the temperature gauge will suddenly go from normal to max"

 

I would suggest replacing the coolant temperature sensor, cheap and easy.

The only thing about this issue that I'm 100% on is that one or the other of us is right!

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OP says: "the temperature gauge will suddenly go from normal to max"

 

I would suggest replacing the coolant temperature sensor, cheap and easy.

 

 

The only thing about this issue that I'm 100% on is that one or the other of us is right!

Hi and thanks for posts. Coolant temperature sensor has already been replaced so guess I'll try cleaning these "prong thingies", if I can find them! Someone has also suggested that the dash MCB solder joints may have dried out/cracked but God knows how I'd go about checking that.

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Hi and thanks for posts. Coolant temperature sensor has already been replaced so guess I'll try cleaning these "prong thingies", if I can find them! Someone has also suggested that the dash MCB solder joints may have dried out/cracked but God knows how I'd go about checking that.

Open the coolant level/expansion bottle, and look inside. If your's is one of the models where they're visible they're very visible.

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So I think you must be looking instead for an intermittent short circuit, I'll have a look at the current flow diagrams in a bit, but I'd imagine somewhere in the engine bay or in the plenum where the wiper motor lives are the likeliest areas for trouble.

 

A cracked solder joint in the cluster can definitely explain coolant shortage indication/alarm, but I don't think it would explain your temp gauge's behaviour.

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So I think you must be looking instead for an intermittent short circuit, I'll have a look at the current flow diagrams in a bit, but I'd imagine somewhere in the engine bay or in the plenum where the wiper motor lives are the likeliest areas for trouble.

 

A cracked solder joint in the cluster can definitely explain coolant shortage indication/alarm, but I don't think it would explain your temp gauge's behaviour.

 

The instrument cluster get's its ECT information from the PCM ECU because the sensor is an analogue device and the cluster is digital with stepper motors for the gauges, the PCM performs the A-D conversion, uses the information for fuel and ignition management and tells the cluster what to display.

Because it resets when the ignition is cycled I suspect there may be a fault code stored.

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Cheers sepulchrave, that makes sense.

 

I can't make my temp gauge go to max even by shorting out the coolant temp connector! Sits stubbornly at 90. :D

 

I guess the engine ECU is smart enough to ignore deeply improbable readings.

Edited by Wino
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Faulty temperature sensor and or coolant bottle .?

 

 

The only thing about this issue that I'm 100% on is that one or the other of us is right!

 

 

Open the coolant level/expansion bottle, and look inside. If your's is one of the models where they're visible they're very visible.

 

 

So I think you must be looking instead for an intermittent short circuit, I'll have a look at the current flow diagrams in a bit, but I'd imagine somewhere in the engine bay or in the plenum where the wiper motor lives are the likeliest areas for trouble.

 

A cracked solder joint in the cluster can definitely explain coolant shortage indication/alarm, but I don't think it would explain your temp gauge's behaviour.

 

 

The instrument cluster get's its ECT information from the PCM ECU because the sensor is an analogue device and the cluster is digital with stepper motors for the gauges, the PCM performs the A-D conversion, uses the information for fuel and ignition management and tells the cluster what to display.

Because it resets when the ignition is cycled I suspect there may be a fault code stored.

 

Can't see any metal sensor prongs in the expansion tank. The garage mentioned that it looked as if the wiring had been played around with; having looked more closely I can see what they mean. I'm sure Skoda don't normally wrap insulating tape around cable runs. post-148309-0-77894500-1474739219_thumb.jpgpost-148309-0-47131200-1474739232_thumb.jpgpost-148309-0-08558000-1474739271_thumb.jpg

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Yep the terminals in that plug have been replaced as some point.

So have I been looking for the wrong thing? I assumed the sensor prongs were further inside the tank. Guess you're talking about the plug attaching to the top of it (L/H side of photo). I can't get to whatever's inside the tank as it seems to be sealed.

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I think Ken was talking about the prongs of the sensor itself, but as you've discovered, they're utterly inaccessible (without a hacksaw) on the Fabia tank.

 

For what it's worth, I think my intermittent short circuit idea is rubbish, having tried deliberately shorting out my coolant temperature sensor and not seen the gauge go to max.

Edited by Wino
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So have I been looking for the wrong thing? I assumed the sensor prongs were further inside the tank. Guess you're talking about the plug attaching to the top of it (L/H side of photo). I can't get to whatever's inside the tank as it seems to be sealed.

So have I been looking for the wrong thing? I assumed the sensor prongs were further inside the tank. Guess you're talking about the plug attaching to the top of it (L/H side of photo). I can't get to whatever's inside the tank as it seems to be sealed.

I'm talking about the coolant temp sensor which given your issue is the more likely candidate than the level sensor.

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I have a feeling that the insulation tape isn't necessarily a later addition, both the missus's Fabia, and my 9N Polo have very similar looking taping to yours (though both cars were acquired by us a long time after they were new):

 

 

Polo: 20160924_191929.jpg

 

Fabia: 20160924_191853.jpg

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