Cooling issues

[sam4191]

Evening!

I have a strange issue. I have had an issue for a while where if i undo the coolant cap when warm, the coolant boils up, rather than just releasing pressure.
Only today, I noticed that on the liquid gauge and VCDS the coolant temp is rising to 110C +, but the cluster gauge is reading bang on 90. I have also noticed that the auxiliary water pump isn't working - probably related? I tried to power up the coolant fan via VCDS, but no life. I have checked fuses on top of the battery and they seem to be ok. I don't use the car a lot, so couldn't say how long it has been like this. It's done a maximum of 800 miles in the last year. :-(

Any ideas anyone?

 

[<tuffty/>]

You need to use VCDS to see what the coolant temps are in both the engine module and the instruments module to see if they correlate as the CTS is a twin sensor one for the ECU and one for the dash... they are typically a few degrees out between them but its a common fault for the CTS to fail... the dash will hold at 90 even when it hits 100+ so as not to scare the typical owner into thinking the car is over heating as this is its typical operating range... it only starts rising when the full speed fan limit is hit and can't get the temps down below 100 so will then start to rise on the dash...

I don't recall which blocks Liquid uses for the sensors as it will use a mix depending on what its trying to display...

If you are legitimately seeing 110deg then the first obvious question is are the fans working?

The fans are turned on at slow speed all the time if aircon is on... if not on then they come in around 96deg coolant temps and is triggered off the switch on the radiator... this is also a common faulty component..

If fans are working and the CTS is validated as reporting correct temps then the other thing it could be is a faulty water pump...

Its not really the best idea in the world to open the cap while coolant is warm but if there is still pressure there then it could indicate a headgasket issue (pretty rare) or a crack in the head (more common)

<tuffty/>