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Hello all.

I have a manual 2016 220bhp petrol VRS.

Over the last year the temp gauge on the dash has been behaving erratically, getting up to operating temp within a few minutes as expected, but then during the drive, it will suddenly swing up to the red and then sweep back to 90.  It can do this often, or every few days.  Totally random.

My local mechanic ran a diagnostic which didn't come back with anything but said that a possible issue is the coolant header tank wiring may have gone, so changed that.  Didn't cure it.

 

Next diagnostic was run "live" with the car up to operating temp, and the data showed the car to Not be overheating but the temp sender sensors showed a difference of several degrees - you'd expect one to be slightly higher given they are front and rear of the engine, but the difference was several degrees, so both were replaced as the cost difference was a few quid.

 

The car was then fine for a short time, until a few weeks later when the gauge went skitzzy again, shooting up to the red and back down, this time with a EML flashing up.  No signs of overheating.

 

A further diagnostic was run and this time showed the Thermostat at fault.   Fortunately I have a warranty which covered the Thermostat replacement and labour.  The water pump was changed at the same time, both parts OEM from Vag Group, with new coolant etc.  (I had to pay for the water pump).

 

The mechanic said that this engine (EA888) is a real pain to bleed.  It did require a bit of a top up after about a week, with a high coolant temp light on the dash one day which seemed to disappear once a top up until a split pipe was discovered, which does explain the level drop to a large degree (the pipe was fixed).

 

It has subsequently done the same thing , resulting in a trip back to the garage for another bleed and here I am now, with the same issue.  I could scream.  

 

The oil temp seemed to be relatively steady at 107, occasionally it goes up a touch, but that seems to be a normal oil temp for this engine.

 

He said that if it does it again, it may need a software update from Skoda - does this seem plausible?  Anyone else had a similar issue?  Is it more likely to be a faulty thermostat?  

 

Any help or advice is gratefully received.

 

Roberto 

Edited 18 August, 20241 yr by Bobbster
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1 hour ago, Bobbster said:

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Hello all.

I have a manual 2016 220bhp petrol VRS.

Over the last year the temp gauge on the dash has been behaving erratically, getting up to operating temp within a few minutes as expected, but then during the drive, it will suddenly swing up to the red and then sweep back to 90.  It can do this often, or every few days.  Totally random.

My local mechanic ran a diagnostic which didn't come back with anything but said that a possible issue is the coolant header tank wiring may have gone, so changed that.  Didn't cure it.

 

Next diagnostic was run "live" with the car up to operating temp, and the data showed the car to Not be overheating but the temp sender sensors showed a difference of several degrees - you'd expect one to be slightly higher given they are front and rear of the engine, but the difference was several degrees, so both were replaced as the cost difference was a few quid.

 

The car was then fine for a short time, until a few weeks later when the gauge went skitzzy again, shooting up to the red and back down, this time with a EML flashing up.  No signs of overheating.

 

A further diagnostic was run and this time showed the Thermostat at fault.   Fortunately I have a warranty which covered the Thermostat replacement and labour.  The water pump was changed at the same time, both parts OEM from Vag Group, with new coolant etc.  (I had to pay for the water pump).

 

The mechanic said that this engine (EA888) is a real pain to bleed.  It did require a bit of a top up after about a week, with a high coolant temp light on the dash one day which seemed to disappear once a top up until a split pipe was discovered, which does explain the level drop to a large degree (the pipe was fixed).

 

It has subsequently done the same thing , resulting in a trip back to the garage for another bleed and here I am now, with the same issue.  I could scream.  

 

The oil temp seemed to be relatively steady at 107, occasionally it goes up a touch, but that seems to be a normal oil temp for this engine.

 

He said that if it does it again, it may need a software update from Skoda - does this seem plausible?  Anyone else had a similar issue?  Is it more likely to be a faulty thermostat?  

 

Any help or advice is gratefully received.

 

Roberto 

Mmm. Well. Sounds like usual thermostat failure maybe the senders were faulty as well. 
 

Why it is still doing it, that I don’t know…. The coolant management is quite complicated in the engine, with two senders on on engine one at rad outlet and the ecu expects a certain differential otherwise will trigger a code.

 

but yours is just the gauge display. And to be honest they are usually only directionally correct anyway and show 90c for anything up to 105c plus….

 

maybe there is a cluster fault or a wiring fault shorting out the temp sender wiring? What if you disconnect one or both senders?  It will probably trigger an eml but what does the gauge do….

9 minutes ago, TheClient said:

Mmm. Well. Sounds like usual thermostat failure maybe the senders were faulty as well. 
 

Why it is still doing it, that I don’t know…. The coolant management is quite complicated in the engine, with two senders on on engine one at rad outlet and the ecu expects a certain differential otherwise will trigger a code.

 

but yours is just the gauge display. And to be honest they are usually only directionally correct anyway and show 90c for anything up to 105c plus….

 

maybe there is a cluster fault or a wiring fault shorting out the temp sender wiring? What if you disconnect one or both senders?  It will probably trigger an eml but what does the gauge do….

Thanks for the reply.

 

The short answer is that I don't know and there's nothing immediately obvious wiring wise that I can see.

 

I'll be phoning the garage tomorrow to get it booked back in, as he did say it may need a software update after the various parts that have been changed.  I do sort of understand that may be the case as so many modern cars need some sort of re-coding after a repair.  

 

Plus, if I go unplugging things myself after a recent fix, without really being an expert on possible results, that could cause further issues.

water pump perhaps?

Just now, Nigel_S said:

water pump perhaps?

It's had a new thermostat and water pump 🤷🏻

It sounds exactly like the water pump sliding sleeve impellor shroud sticking after being deployed from a cold start, does the problem occur shortly after the warm up period or the first time the engine is put under additional load after the warm up?

Edited 18 August, 20241 yr by J.R.

4 minutes ago, J.R. said:

It sounds exactly like the water pump sliding sleeve impellor shroud sticking after being deployed from a cold start, does the problem occur shortly after the warm up period or the first time the engine is put under additional load after the warm up?

It seems to happen after the car has warmed up, I've never had it happen immediately on start up.

As mentioned in my question, the water pump was changed at the same time as the thermostat.  Why would the shroud stick?  Does it mean changing the water pump as it's faulty?  Seems unusual for a brand new part?

 

Thanks for the reply.

You have confirmed my hypothesis, it happens shortly after the warm up period, that is when the deployed sleeve should retract under the action of the return spring, if it doesn't it overheats before finally coming unstuck, pumping water as it should and the temperature returning to normal.

 

Why would it stick, because they do, the more complicated things become the more potential failure modes, the price you pay to have warm feet quicker on a winter morning.

 

Nothing unusual about a new part failing, aftermarket parts are at best only as good as new, most of the time lesser quality made to a price and they dont have to offer the same guarantee as the manufacturer or worry about their reputation, if you look at the distribution on a MTBF (mean time between failure) graph you will see a very prominent peak in the first few months.

 

You can change the water pump or remove the wiring connector to the actuator, then it will never deploy and stick, downside is slightly longer warm up time.

Remove the connector after having done a run where the engine did not overheat, do not remove it with the engine running during warm up.

 

The above is on my assumption that your engine has the sliding sleeve water pump, you can check by looking for the connector.

16 minutes ago, J.R. said:

You have confirmed my hypothesis, it happens shortly after the warm up period, that is when the deployed sleeve should retract under the action of the return spring, if it doesn't it overheats before finally coming unstuck, pumping water as it should and the temperature returning to normal.

 

Why would it stick, because they do, the more complicated things become the more potential failure modes, the price you pay to have warm feet quicker on a winter morning.

 

Nothing unusual about a new part failing, aftermarket parts are at best only as good as new, most of the time lesser quality made to a price and they dont have to offer the same guarantee as the manufacturer or worry about their reputation, if you look at the distribution on a MTBF (mean time between failure) graph you will see a very prominent peak in the first few months.

 

You can change the water pump or remove the wiring connector to the actuator, then it will never deploy and stick, downside is slightly longer warm up time.

Remove the connector after having done a run where the engine did not overheat, do not remove it with the engine running during warm up.

 

The above is on my assumption that your engine has the sliding sleeve water pump, you can check by looking for the connector.

That's very informative, thanks for that.  The new parts are official VW parts rather than aftermarket FWIW, but you're right, parts do fail.

 

I've got it booked back in next week, the mechanic says it may be an ECU issue but I'll mention this message and see what his take on it it.

 

I'm guessing this type of fault doesn't trip the EML, it's down to a bit of experience and guess work 🤷🏻

Even official VAG parts may not be the same as those fitted on the production line especially for an 8 year old vehicle, batteries are a great example, the same VAG part number, the same manufacturer yet the sticker will be different, the battery will be lighter and will likely not last as long.

4 minutes ago, J.R. said:

Even official VAG parts may not be the same as those fitted on the production line especially for an 8 year old vehicle, batteries are a great example, the same VAG part number, the same manufacturer yet the sticker will be different, the battery will be lighter and will likely not last as long.

Roger that.

22 hours ago, Bobbster said:

That's very informative, thanks for that.  The new parts are official VW parts rather than aftermarket FWIW, but you're right, parts do fail.

 

I've got it booked back in next week, the mechanic says it may be an ECU issue but I'll mention this message and see what his take on it it.

 

I'm guessing this type of fault doesn't trip the EML, it's down to a bit of experience and guess work 🤷🏻

The electromechanical thermostat in the gen3 does not use return spring AFAIK. It uses a servo and gears and the exact position of the restriction valve can be monitored and logged.

 

If it was to say get stuck, gears strip etc, they do "usually" log a fault. As the thermostat would not be responding to position changes as requested. Or the coolant temp differential was not as expected.

 

If you log both temp sensor value when this spike happens with the temp guage you should be able to determine if it is genuine temp overheating or not. 

 

 

 

Edited 20 August, 20241 yr by TheClient

22 minutes ago, TheClient said:

The electromechanical thermostat in the gen3 does not use return spring AFAIK. It uses a servo and gears and the exact position of the restriction valve can be monitored and logged.

 

If it was to say get stuck, gears strip etc, they do "usually" log a fault. As the thermostat would not be responding to position changes as requested. Or the coolant temp differential was not as expected.

 

If you log both temp sensor value when this spike happens with the temp guage you should be able to determine if it is genuine temp overheating or not. 

 

 

 

 

20 minutes ago, TheClient said:

The electromechanical thermostat in the gen3 does not use return spring AFAIK. It uses a servo and gears and the exact position of the restriction valve can be monitored and logged.

 

If it was to say get stuck, gears strip etc, they do "usually" log a fault. As the thermostat would not be responding to position changes as requested. Or the coolant temp differential was not as expected.

 

If you log both temp sensor value when this spike happens with the temp guage you should be able to determine if it is genuine temp overheating or not. 

 

 

 

To log these live temps, what type of reader would I need?  I'm assuming that I would need to go for a drive and be able to record them review all that data across the drive to really know.

It's genuinely incredibly frustrating, I've never had this issue on any car before.

 

Obd eleven, vcds will for sure. Something simpler like torque pro would probably allow you to log at least one of the senders not sure if both though.

 

Yes, you'd want to log when the spike occurs and compare to data in the log to indicate if the temp is really high on either sensor.

 

They do run hot by design, the thermostat regulates to about 103C to 105C from memory. The rad outlet should be a noticeable amount cooler. 

 

 

15 minutes ago, TheClient said:

Obd eleven, vcds will for sure. Something simpler like torque pro would probably allow you to log at least one of the senders not sure if both though.

 

Yes, you'd want to log when the spike occurs and compare to data in the log to indicate if the temp is really high on either sensor.

 

They do run hot by design, the thermostat regulates to about 103C to 105C from memory. The rad outlet should be a noticeable amount cooler. 

 

 

Ok thanks.

 

It's interesting.  Both sensors were replaced less than 6 months ago.  Along with a new coolant tank,water pump and thermostat.  Basically a whole new system and still the gauge Fluctuates. 😵‍💫

I don't think that engine even has the sleeve type water pump, my guess is you have some bad wiring/connection to one of the sensors. And every now and again it is moving around causing guage to spike up.

24 minutes ago, Blue8793841 said:

I don't think that engine even has the sleeve type water pump, my guess is you have some bad wiring/connection to one of the sensors. And every now and again it is moving around causing guage to spike up.

I thought it was likely to be a wiring fault more than anything else, given what's been replaced.  It seems highly unlikely that the issue would persist for so long and that so many elements would be faulty.  A damaged wire seems plausible 

On 18/08/2024 at 14:47, TheClient said:

 

maybe there is a cluster fault or a wiring fault shorting out the temp sender wiring? What if you disconnect one or both senders?  It will probably trigger an eml but what does the gauge do….

 

6 hours ago, Bobbster said:

I've never had this issue on any car before.

 

We none of us have had vehicles with so much extraneous complicated emissions control and electronic equipment.

 

A faster warm up is desirable for emissions, fuel economy and driver & passenger comfort but the benefits of these systems are quite marginal over a standard wax capsule thermostat.

 

The sliding sleeve water pump was a good idea but an Achilles Heel, they have replaced it with something even more complicated and flaky.

21 hours ago, J.R. said:

We none of us have had vehicles with so much extraneous complicated emissions control and electronic equipment.

 

A faster warm up is desirable for emissions, fuel economy and driver & passenger comfort but the benefits of these systems are quite marginal over a standard wax capsule thermostat.

 

The sliding sleeve water pump was a good idea but an Achilles Heel, they have replaced it with something even more complicated and flaky.

What is definitely the case with gen 3 water pumps, they definitely have a finite life due to all the plastic, plastic bushings, lack of replaceable seals etc. Also due to the amount of active management the servo movement is used a lot, even after warm up...

 

A replacement thermostat only gives you a new lifetime which on these, I'd say 5 or 6 years, 60 to 70k miles is it.

 

It will be interesting to hear what the op fault is, considering it has already been replaced. 

On 21/08/2024 at 20:06, TheClient said:

What is definitely the case with gen 3 water pumps, they definitely have a finite life due to all the plastic, plastic bushings, lack of replaceable seals etc. Also due to the amount of active management the servo movement is used a lot, even after warm up...

 

A replacement thermostat only gives you a new lifetime which on these, I'd say 5 or 6 years, 60 to 70k miles is it.

 

It will be interesting to hear what the op fault is, considering it has already been replaced. 

So after buying an OBD11 reader, the scan came up straight away with fault code P255600, Engine Coolant Level Sensor/Switch.

 

I cleared the code and went for a 15 min drive with live data for the coolant.  The temp gauge didn't sweep during the (short) run out, which was a mix of 30-National Speed limit roads near me.  The coolant generally seemed to sit between 103-108 at a steady speed, with it reducing to 95ish when accelerating in third from 30-60, then moving up to 103+ when back to cruising.  Oil temp reached 106, which has always seemed to the where it sits unless it's hot outside.

 

I'm still digging into the menus and options, there is one to run live data between the engine and radiator sensors, which I'll do tomorrow - I briefly checked it at the end of the drive and it showed 3 Deg difference, which I suspect is fairly normal given their different positions in the engine bay etc.

 

I did have both of these sensors replaced within the last couple of months so hopefully it's one them that's at faulty.

 

I'll update after the car goes in to the garage this week.

How did you solve the problem?