Hi all,

 

Just asking about the temperature gauge in my 2017 1.2 Tsi 4 cyl 16V.

 

In our older car, it just has a "cold" light which saves a lot of hassle and questions 😉

 

In this newer model, I've noticed that the gauge sometimes gets to about 2/3rds of the way towards 90 and then drops back before coming up again and settling at 90 deg C. This is over the space of 10s of seconds and I assumed it was  due to the temp sensor being in the head and the thermostat opening (causing the fall back) before it all gets up to operating temp.

 

On other occasions, the temp gets up to 90 deg, then falls back to about 5/8ths of the way to 90 then comes back up again, again over 10s of seconds.

 

So, I would have thought that a simple thermostat would open at roughly the same temperature each time (like the wax/spring ones I used to change on my old Ford crossflow engines!) but I presume they are more sophisticated these days with the ECU controlling the thermostat and varying the temperature at which it opens?

 

Or, is the thermostat just really very variable / faulty ?

 

Thanks for any replies.

 

 

To speed up engine warm up to reach thermal efficiency faster, initially, the coolant only circulates around the engine block. Then once the temperature reaches a trigger threshold, the remainder of the system comes into circulation too. At that point, the 'cooler' coolant starts to circulate with the hotter coolant, hence you see the drop on the thermometer. So what you see is normal.

3 hours ago, TerFar said:

To speed up engine warm up to reach thermal efficiency faster, initially, the coolant only circulates around the engine block. Then once the temperature reaches a trigger threshold, the remainder of the system comes into circulation too. At that point, the 'cooler' coolant starts to circulate with the hotter coolant, hence you see the drop on the thermometer. So what you see is normal.

Hi,

 

Yes, this was expected. What wasn't expected was the variance in it and whether that was normal.

 

Cheers

I understand. My experience is that it isn't consistent. Sometimes it seems to drop a huge amount, sometime just a little blip. This may be a Laggy temp gauge or the different core temperature when you start up. 

3 minutes ago, TerFar said:

I understand. My experience is that it isn't consistent. Sometimes it seems to drop a huge amount, sometime just a little blip. This may be a Laggy temp gauge or the different core temperature when you start up. 

 

It's good to know that it isn't consistent. I sort of expected that control of the flow out of the head would be more complicated these days (e.g. ECU controlled) - just wanted to make sure while the car was still in warranty.

 

 

If you take your foot off the throttle but still have the car in gear no fuel goes to the engine.

The engine will start to cool at this point, especially if you have recently started the engine from cold.

 

There are two thermostats in the Fabia TSI engine that open at different temperatures.

Taken from VW new EA211 engine info PDF I have:-

 

Cooling system
A dual-circuit cooling system is used for engine cooling in all EA211 engines. With this system, the coolant is
channelled separately through the cylinder block and cylinder head at different temperatures. The temperature
regulation is controlled by two thermostats in the thermostat housing. The respective coolant temperatures differ
according to the engine

 

Thermostat 1 for cylinder head
It opens at a temperature of 87 °C or above, and
opens the path from the radiator to the coolant pump.

 

Thermostat 2 for cylinder block
It opens at a temperature of 105 °C or above, and
opens the path for the warm coolant from the cylinder
block to the radiator. 

 

Thanks AG Falco

Even more complex than I thought! So there are effectively three coolant pathways, engine block, head and radiator. No wonder the progress of the temp gauge appears to be inconsistent! 

Thanks for the clarification, chaps.

 

22 hours ago, TerFar said:

Even more complex than I thought!

 

The water supplied to the cabin heater is another complexion as well as:-

 

Water radiator for charge air cooling circuit and a Charge air cooling pump. ( Turbocharger cooler / intercooler. )

 

So there are two water pumps as well as three radiators / heat exchangers / coolers. 😮

 

Car engines are getting simpler, honest. 😉

 

Thanks AG Falco