CBZB Cooling System

This is my try to understand how cooling on CBZB engine is working.
I saw a lot of sources and most of them has partial information so here I will summarize all I know.

Important! That is not official documentation, only my findings. Use it on your own risk please :-)

General notes about working on cooling system

Hot steam may escape when the coolant expansion reservoir is opened. Wear safety goggles and safety clothing, in order to avoid eye injuries and scalding. Cover the cap with a cloth and open carefully.
 - When the engine is warm the cooling system is under pressure. If necessary reduce pressure before repairs.
- The hose connections are secured with spring-type clips. In case of repair only assign the spring strap clamps via the → Electronic catalogue of original parts.
- Use pliers for spring strap clamps to fit the spring strap clips.
- Always replace seals and gasket rings.
- When installing fit the coolant hoses free of stress, without them touching any other components (pay attention to the marking on the coolant connection and hose).
- The arrows which are on the coolant pipes and the coolant hose ends must stand opposite to each other.

General info

1.2L TSI engine has two independent cooling systems which are connected and disconnected by non-return valves and a flow restrictor:
1. the charge air cooling system.
2. the engine cooling system which, in turn, is subdivided into 2 circuits.
Temperature difference between two systems can rich up to 100 °C.

Charge air cooling system

I think this pump very important as keeping cool charger that can go up to 900 °C, so let's go deep here.
Please welcome - the coolant circulation pump V50

In real life on my car it looks like this

This is current flow diagram (mostly the same for all engine production dates).

CBZB engine from May 2010 upto Nov 2010

Brown wire goes to "281 - Earth point 1, engine prewiring harness".
White with red tracer to "J496 Additional coolant pump relay". This relay is the only one on the battery.

1: 3B0 951 253 - Contact close relay (~$18)

Operational cases (not confirmed, from 1.2 TSI and 1.4 TSI docs)
- briefly, after each engine start
- constantly, after engine load request above 100 Nm
- constantly,  if charged air temperature (G42 sensor) above 50°C
- constantly,  if before (G299 sensor) and after (G42 sensor) charged air temperature difference above 8°C
- briefly, on running engine every 2 minutes for 10 seconds to keep turbocharger from overheating
- briefly, after engine stop for 0-8 minutes to cool turbocharger and reduce possible vapor locks cause of temp difference
- can be activated by signals from coolant temp sensor G62 or oil temp and level sensor G266 (only models with extended servicing intervals).

There is no PCM self-diagnostic routine for the pump. If V50 or relay J496 fails overheating can happen. This cooling system failure found be checking compressed air temperature before and after cooler (G299 and G42 sensors).

Engine cooling system

The separate coolant flows inside the cylinder head and inside the engine block allow different temperatures to be achieved in both of these components by using a thermostatic housing with dual thermostats.

The cylinder head thermostat begins to open when the coolant temperature reaches approx. 80°C. It achieves its maximum opening cross-section at a temperature of 135°C.

On the other hand, the thermostat for the cylinder block begins to open at 87°C. In this case, too, the thermostat achieves its maximum opening cross-section at a temperature of 135°C. With this configuration, the circulation of coolant through the cylinder block is suppressed during the engine warm-up phase by the closed cylinder block thermostat. The cylinder linings can therefore heat up more quickly, and the friction of the piston assembly can be significantly reduced while the cylinder head is cooled more intensively in order to provide better knock resistance.
There is temp sensor near thermostat 2 (cylinder head).

1: 03F 121 111 A - Coolant thermostat housing with thermostat (~$216)
4: 03F 121 119 - Gasket (~$4)
5: N 910 717 01 - Hexagon socket flat head bolt (Remark: M6X25) (~$1)

There are 2 temp sensors:
1. G62 - near thermostat 2 (cylinder head)
2. F18 - thermal switch in radiator. Octavia II has G83 temp sensor, not 2 stage switch like here.

Engine cold

After cold-starting the engine, the active coolant pump is activated, thus stopping the coolant flow.

If no heating is requested, the engine heats up very quickly. If heating is requested, coolant circulation is stopped for approx. two minutes. Both thermostats are closed.

The coolant flows through the coolant pump, the cylinder block and the heater heat exchanger, and then back to the coolant pump. Parallel to this, the coolant flows through the oil cooler.

Engine warm, a cylinder head thermostat opens

If the coolant has reached a temperature of 80 °C, the cylinder head thermostat opens. The main radiator is now integrated in the coolant flow.

Engine warm, both thermostats open

When the coolant in the cylinder block reaches a temperature of 87 °C, the thermostat for this circuit opens with the result that the cylinder is now incorporated into the coolant circulation system.

Thermal management

The task of the thermal management system is to enable the engine to attain its operating temperature quickly since this improves fuel economy and reduces exhaust emissions.
Thermal management is implemented by stopping the circulation of coolant during the warm-up phase:
- up to a coolant temperature of 90 °C at "salon heater off"
- up to 2 minutes at "salon heater on"
This is implemented technically by using an active coolant pump.

On top - Coolant circuit solenoid valve N492 - controls vacuum

1: 03F 121 004 E - Water pump with adhesive gasket (since 22.11.2011, was 03F 121 004 B) (~$208)
2: 03F 121 031 A - V-belt pulley (~$20)
41: 03F 121 713 - Control line (~$119)
42: 037 906 283 C - Solenoid valve
43: 046 905 291 B - Check valve (~$9)

Functions:
- coolant flow interrupted - coolant temperature of less than 30 °C, activated by vacuum.
- coolant is pumped - vacuum supply is shut off.

Special restarting characteristics:
- switches on and off for the duration of one second
- this cycle is repeated several times in succession
- the interval between cycles is approx. 7 seconds

Thus, the warm coolant from the engine mixes slowly with the cold coolant. When heating is requested, the pump is switched on immediately.

Vacuum activation.
The coolant pump is activated by the coolant circuit solenoid valve N492. It is operated by the engine control unit (this is computed by a map). The pump is activated by means of a PWM signal*.
However, the orifice plate is not actuated variably. It is only switched on or off.
If the valve is deenergised or fails, the coolant flow cannot be controlled since the orifice plate is kept retracted by the spring pressure (maximum coolant flow).
- Failure in off-state: the engine reaches its operating temperature more slowly.
- Failure in on-state: the coolant temperature increases to an unacceptably high level since the coolant pump is unable to feed in fresh coolant. The exhaust warning lamp K83 comes on.

Radiator fan

And this not less important device is not described in SSP docs.

16 - Radiator fan V7
24 - Thermo-switch for radiator fan F18

1: 6R0 959 455 C - Electric fan (Remark: 260/90W 390MM Siemens) (since 10.01.2011, prev was 6Q0 959 455 AD) (~$238)
4: 1J0 906 443 - Flat contact housing for single wiring (Remark: 3 pin, 000 979 228 E, 000 979 307 E)
10: 1J0 959 481 A - Dual thermal switch (Remark: 84-95C/91-102C 3 pin) (~$27)

Switching temperatures
Stage 1 - 84...95 °C
Stage 2 - 91...102 °C

UPDATE 2020-08-15

Below is thermal switch (position 10) compatible parts (price ordered high to low as of today).

Be aware that most of them has different work temperature ranges. Original is 84-95/91-102C, Hella has 87-97/97-102C. In my opinion, lower temp switch is better as it should keep slightly cooler engine but its not super critical.

Hella 6ZT 007 800-111

Hella - 6ZT 007 800-111 ~$28

Delphi - TS10292 ~$23

VAG - 1J0 959 481 A ~$22 (original)

Febi - 36563 ~$20

SWAG - 30 93 6563 ~$20

Vemo - V15-99-2006 ~$14

Metzger - 0915041 ~$14

Borsehung - B13129 ~$12

Facet - 7.5690 ~$12

Eps - 1.850.690 ~$12

Meyle - 100 959 0016 ~$10

Autlog - AS2014 ~$10

Vernet - TS2783 ~$10

Sat - ST-1J0 959 481 A

Fae - 38185

Jp Group - 1194000800

Topran - 109 772

Meat&Doria - 82701

Patron - PE20062

Era - 330230

Maxgear - 50-0176

Hans Pries - 109 772 755

Vika - 99590082401

Ossca - 02905

Elfull - ELS2030

Howyaa - 84081

END OF UPDATE

With out climatronic and climatic, fan get command from switch, proof

I have Climatronic, so there is radiator control unit J293 involved

And flow is different

Prev picture missing that 2,3 and 5 are positive leads, goes to fuse holder

The question is - how fan logic is working?
Radiator fan control unit (J293) connected to Climatronic control unit (J255) by 2 wires. The last connected to onboard supply control unit (J519) by CAN bus.

From Skoda SSP 25 - Climatronic I found 2 cases:
1. Air conditioning is off.
- first fan speed (90W) engaged at 84...95 °C (see stages of F18 above)
- second speed (260W) at 91...102 °C.
2. Air conditioning is on, pressure sensor G65 (old name F129) come in - pressure in refrigerant lines.
- pressure above 16 bar - second fan speed
- pressure above 2 bar and air condition was just turned on - first speed

Climatronic shuts off compressor completely when coolant temp come to 119°C and re-enable at 112°C again.

Changing coolant

For CBZB it's 7.7 ltr of G12++ or G13 with water mixture.
Also interesting that this engine has biggest capacity over others. Take for example CAVE that is way too super hot but has less coolant (and less 0.3l oil too!) - crazy, but good for us, CBZBers :-)

Draining and filling up coolant (PDF)

Coolant mixture

Many people suggest to use distilled water instead and this is true. Remember, DO NOT mix normal tap water with coolant. Tap water varies in pH, mineral, and chemical content and can adversely affect your new coolant and cooling system. City water may be treated with chlorine which is corrosive.

G12 consists of Ethylene Glycol and some additives. From this table you should see the following. Water is the main thermal transfer fluid in coolant system, when you mix water with Ethylene Glycol say for 50/50, conductivity drops almost a twice that mean mixture transfer less heat. So you need to find proper mixture. It's tricky because boiling point is also important. Refer for manufacturer instructions.
I would suggest in Israel (no freeze points) for CBZB use 40-20% of G12.


Sources
My old engine post with SSP materials - most images and text
Skoda Fabia II - Workshop manual - Power train - CBZB CBZA - 1.2 TSI (Edition 09.2012)
Skoda Fabia II - Workshop manual - Circuit diagram - Basic equipment, From March 2010 (Edition 03.2012)
ETKA (Skoda 2012-03)
ELSA Skoda (up to date)
Ethylene Glycol Heat-Transfer Fluid

Prices actual to post date and shown for original parts, there are cheaper replacements with same quality without VW logo on market too.

P.S. Not a April 1st joke :-)

41 700 km | 2Y 4M