Škoda Octavia MK III TDI - Overheating after coolant flush

[smecs]

Hello guys, 

 

My problems occurred during the summer time while after the DPF reg the car started to boil the coolant and evacuate it over the coolant cap. That thing was sorted out with the Heater Matrix replacement. 

The cold weather came and the car won't blow heat into the cabin on the passenger side ( LHD) as into the driver side( the difference between the 2 sides was at least 15 degrees). 

I gained information as much as I could and in a good weather day I started to flush the whole coolant system of the car. 

I was having 40 L of distillate water and 3x 1.5L G12++ coolant + a good radiator flush from LiquiMolly. Also had an VCDS interface to run the bleeding procedure for the main system and for the low temperature system. 

 

Started with the actual coolant drain from the car, which BTW was not in the baddest condition(like color) but it had some deposits like sand into it. 

Disconnected the hoses from the main radiator, charge cooler radiator and from the auxiliary pump. 

 

Until this, everything was fine. Flushed the system with distillate water for 3 times. 

At the end, I made the coolant level with 50% distillate water and 50% G12++ coolant, but the thing is Skoda Manual it's saying the actual capacity of the coolant system it's about 8.4 L and I managed to fill with about 4.5 liters trough the coolant cap even after several Bleeding Procedures with VCDS. 

 

The car ran well in this condition for about 50 km when I stopped for about 2-3 hours and when I started again, the coolant level in the coolant cap was under MIN( I presume the low coolant system sucked the coolant when I stopped the car). Put in the coolant mix until MAX and got back another 50 km without any issues. 

 

The next day, at a low speed but uphill I noticed the gauge from the water temperature it's raising but I didn't let it generate message to stop and I turned the heating to HI and full power on the ventilation. Opened the bonnet and the level was above the MAX( at this time the main FAN on the radiator was at high speed).  

At that moment I was expecting a Thermostat issue, as the car has about 9 years without changing it( it's my car since new). Got a mechanic took out the thermostat( this happened on Saturday after 16:00 PM so no shop with car parts available), but running a road test the car was having the same symptoms ( temperature raise above 110 degrees on VCDS) as the car was not running water through the radiator even if the thermostat was not present. I presume there is air into the system( BTW the refill of the coolant was not done with pressure air, just manual..) and I run about 4 bleeding procedures but no joy. 

After a couple of hours of staying off the car was running like a car without thermostat. Bought a new OE thermostat the other day and put in and the it has the same problem, temperature raises and the water it's not passing through the Thermostat to reach the radiator. 

I followed some YT video with the thermostat replacement and I can say it's properly mounted, no leaks in that area. 

 

The water pump was changed in 2019 with a new OE one, so it has 3 years and about 60.000 km( when suddenly cracked and the red message came)

Tried with a brand new  coolant cap and no joy.

Tried several times to run bleeding procedure with VCDS( it's saying finished OK) but it's not making any differences, car still overheats. 

I'm not having symptoms like water in the Oil or oil in the water. 

 

I tried to run into the neighborhood without the coolant cap, the temperature stopped raising at about 104 degrees on VCDS while I opened the bonnet and saw the coolant tank empty and the hoses from the thermostat to the radiator HOT. While I was putting water into the coolant tank, the temperature on VCDS immediately dropped under 90 degrees( as it's normal). I put the coolant cap on again and start a trip on the highway. After about 5 km again the temperature was raising again to about 110 degrees and the thermostat won't open. 

 

I know it's a long story but I'm having this issue for about 2 weeks while I was reading many topics related to this problem and still can't figure out what's the issue. 

I booked in a visit with the local Skoda Dealer for a review but it will be on 15 of December. 

 

If anyone can have an advice into this matter or now how can I try to bleed the system properly without an air system I would much appreciate.

The car was running normally until I flushed the system. The problems happened only after this.

[Vahids]

Sorry for the trouble!

 

I can think of two issues, 1) since you have flushed the coolant with water and only consumed less than 5 litres of coolant it means half of the coolant is water which is not as effective as (properly mixed) coolant for cooling down the system (Also are you sure the coolant you mixed wasn't already diluted and not for anymore mixing?), 2) it is very likely that you have air lock in the system. You can use coolant suction tools to properly fill the system. They are cheap themselves, but they need compressed air to work (which is a bit an issue for people who don't have the air compressor). 

 

Also, have a question. Where you say "Also had an VCDS interface to run the bleeding procedure for the main system and for the low temperature system.", what do you mean by "bleeding with VCDS"? how do you do that? I didn't know you can do bleeding with VCDS.

Edited 23 November, 2022 by Vahids

[J.R.]

Your Silkat bag has burst and the system needs a complete and thorough chemical flushing and probably replacement of the heater matrix.

 

There is a strong possibility that the water pump shroud has stuck on the new pump, to confirm this wait until the car is bhaving correctly and engine at operating temperature and then remove the electrical connector to the water pump, if the problem does not recur then you need to either replace the pump or leave the cable disconnected.

 

Long term you still have issues with the Silkat crystals blocking the cooling system so this should also be attended to.

[J.R.]

An engine will not overheat because the anti-freeze concentration is weak or even running on plain water, the thermostat might open a miniscule amount further to maintain the operating temperature but it is not something that could even be measured.

[smecs]

7 hours ago, Vahids said:

 

 

Also, have a question. Where you say "Also had an VCDS interface to run the bleeding procedure for the main system and for the low temperature system.", what do you mean by "bleeding with VCDS"? how do you do that? I didn't know you can do bleeding with VCDS.

Yes, there is an option where you can run bleeding process.

 

@J.R. Definetely it’s not the case with silikat bag. I’m not having the reservoir with that bag. It’s the reservoir from the factory.

 

I parked the car in the garage and left it through the night without the shield under the engine. No leaks on the floor. Just one strange case: I could hear a noise from the coolant reservoir and I presume the cap or the reservoir could not mentaim the pressure. 
It could be a good idea to change both( I will have them changed). 
 

2 hours ago, J.R. said:

Your Silkat bag has burst and the system needs a complete and thorough chemical flushing and probably replacement of the heater matrix.

 

There is a strong possibility that the water pump shroud has stuck on the new pump, to confirm this wait until the car is bhaving correctly and engine at operating temperature and then remove the electrical connector to the water pump, if the problem does not recur then you need to either replace the pump or leave the cable disconnected.

 

Long term you still have issues with the Silkat crystals blocking the cooling system so this should also be attended to.

My water pump has 3 years old and 60.000 km. The thing is each time the behave not normal. I can’t make the pump work by off and on the engine.  
Maybe my pump it’s fully stuck..but without the coolant cap I can make the thermostat to open. When I put the cap on, it’s starting to overheat.

 

Thank you guys for the answers.

[bigjohn]

This causes havoc and stops internal heater:-

 

 

[J.R.]

2 hours ago, smecs said:

@J.R. Definetely it’s not the case with silikat bag. I’m not having the reservoir with that bag. It’s the reservoir from the factory.

 

 

23 hours ago, smecs said:

That thing was sorted out with the Heater Matrix replacement. 

 

On 22/11/2022 at 19:34, smecs said:

the car won't blow heat into the cabin on the passenger side ( LHD) as into the driver side( the difference between the 2 sides was at least 15 degrees). 

 

23 hours ago, smecs said:

Started with the actual coolant drain from the car, which BTW was not in the baddest condition(like color) but it had some deposits like sand into it. 

 

= Silkat contamination in my opinion.

[smecs]

Can it be reservoir with silikat bag even if it has not “Mitt silikat” tag in it? 
I’m not having Mitt silikat tag on the reservoir and it was not changed 100%.

[ApertureS]

Everyone is forgetting the correct procedure. Chances are there is an airlock in the system, there is a diagnostic procedure to allow correct venting of the coolant system.

if this isn’t run for its full cycle you risk air locks in the high temp and low temp coolant circuits.

 

I don’t think vcds can do it, odis can though.

 

regarding concentration -  water is what has the heat transfer capabilities, anti freeze is the additive mix that prevents rust, freezing and other bits.

just having water in the car will still allow the engine to transfer heat perfectly fine (not that you should have just water)

[ords]

2 hours ago, smecs said:

Can it be reservoir with silikat bag even if it has not “Mitt silikat” tag in it? 
I’m not having Mitt silikat tag on the reservoir and it was not changed 100%.

Look inside and see if you can see the silicate bag.

[J.R.]

Mine does not have the writing, I cannot see a bag inside, it does not appear to be double skinned but I am still wary and constantly on the lookout for signs of problems, finding sand deposits in coolant drained from the system would put me into Defcon 1!

[smecs]

2 hours ago, ApertureS said:

Everyone is forgetting the correct procedure. Chances are there is an airlock in the system, there is a diagnostic procedure to allow correct venting of the coolant system.

if this isn’t run for its full cycle you risk air locks in the high temp and low temp coolant circuits.

 

I don’t think vcds can do it, odis can though.

 

regarding concentration -  water is what has the heat transfer capabilities, anti freeze is the additive mix that prevents rust, freezing and other bits.

just having water in the car will still allow the engine to transfer heat perfectly fine (not that you should have just water)

Initially I thought VCDS would make the Bleeding process ok but now I’m having doubts. 
I will ask the local dealer to run a odis bleeding and hope it will be ok after.  
 
Is there any way I can diagnose the switchable water pump? 

[Ootohere]

Small point.  Anti freeze coolant rust inhibitor.   It is all in there.   Once all is well.    It is basic stuff.  A pressurised system.   Freezing Temperature and the boiling point is not that of H2O.   Anti freeze / summer coolant and the rust inhibitor being what it is in there.    And if H2O the right water.  

 

 

 

[Warrior193]

7 hours ago, ApertureS said:

Everyone is forgetting the correct procedure. Chances are there is an airlock in the system, there is a diagnostic procedure to allow correct venting of the coolant system.

if this isn’t run for its full cycle you risk air locks in the high temp and low temp coolant circuits.

 

I don’t think vcds can do it, odis can though.

 

regarding concentration -  water is what has the heat transfer capabilities, anti freeze is the additive mix that prevents rust, freezing and other bits.

just having water in the car will still allow the engine to transfer heat perfectly fine (not that you should have just water)

In fact, plain water has better heat transference than glycol mix - as concentration goes up, heat transfer rate goes down. The glycol mix does have a higher boiling point though.

As Aperture says, straight water as coolant will cause other problems.

[ApertureS]

14 minutes ago, Warrior193 said:

In fact, plain water has better heat transference than glycol mix - as concentration goes up, heat transfer rate goes down. The glycol mix does have a higher boiling point though.

As Aperture says, straight water as coolant will cause other problems.

I didn’t wanna get too technical with it but yeah you’re spot on 😛 people seem to forget what anti freeze is, cause it definitely is not coolant!

[smecs]

Thank you again for the replys. 
Now I suspect the wather pump, even if it was changed 3 years ago with OE..

 

Is there any way to see if it’s working(water pump)?

[J.R.]

The water pump is working, its pumping water when the engine is maintaining the correct temperature, the sleeve which stops the flow during the warm up period can stick in the deployed position causing overheating, this would normally be apparent the first time you put the engine under load after the system has reached operating temperature, I think you described joining a motorway by the slip road.

 

I explained earlier how you could disable it in the safe position to diagnose if it was the faulty item.

 

There is also a DSG thermostat which can cause similar problems, I cant see from this posting window whether your car is a DSG, if it isn't then ignore that.

[smecs]

I just tried to unplug the connector of the water pump. Only difference was the fault code on VCDS.  
With water temperature on VCDS at 90 degrees, I unpluged the inlet hose from the expansion tank and no water flow from it. 
I think I have a totally stucked sleeve in the closed position.
Btw, the heating in the cabin was off(climatronic turned off) while I was doing this test, when I put the heating on 24 degrees, I had water flow from the inlet hose.

 

It’s a 5 speed manual, so no DSG thermostat.

[J.R.]

I dont think there is a coolant flow through the expansion tank, it is what its name suggests and nothing more.

 

I would have to read one of my self study guides to be sure but they are 800kms away!

Edited 24 November, 2022 by J.R.

[smecs]

I saw a guy on youtube who changed the water pump on a Golf 7 TDI with an aftermarket one without the electric sleeve. 
With the electrical sleeve partially stuck, there was no flow on the inlet hose on the expansion tank.

After he put aftermarket pump without sleeve, there was water flow on that hose even with cold engine. 
 

I know the sleeve actual block the water flow to let the engine warm-up quickly, but I checked when the temperature was at 90 degreese, so the sleeve has to be opened.

[smecs]

UPDATE 

 

Changed the water pump. It was stuck on closed. OE pump lasted 3 years and 40.000 km( aprox). The issue of this failure was the coolant. Maybe a bad proportion of coolant and water or the coolant itself ( G13). 
The next step it’s to wash all the system properly and to change front radiator, but all of these after the wedding. 
 

Thank you all for your support.