Heating issue

[CarlW]

I have an issue with the temperature gauge rising and falling when the heating is on in the car.. I've been out in it a few times with the heating on full on the highest heat setting and the gauge seems to rise and fall as well as the heat depending on RPM's and speed. Without the heaters on, the temp gauge stays firmly at 90.

I had the same problem this time last year and had the main thermostat changed with a new genuine one and the problem still remained.. Snow went and weather warmed up so I forgot about it as I don;t use the heaters much but now the snow is back and it's cold, naturally putting the heaters on, i've found the problem is back to haunt me.

I'm uncertain if the coolant temp sensor has been changed so that is my next port of call.
The air con has not been looked at in my ownership yet so I'm wondering if this could lead to anything that I could have seen to by a garage and also have the system topped up as it's probably needed.

Is there anything else that this problem could relate to?

[GSP1973]

I've noticed the same problem since the weather has changed. I turn on the economy setting for a while and it seems to help. Hopefully it's nothing serious.

Sent from my SM-G361F using Tapatalk

[CarlW]

Thats all well and good but I rather a problem be fixed to work as it should.. Hope you get yours sorted too.
I will update the thread if it will help you or anyone else with a fix solution once I get a garage to look at it and sort it out.

[seiko]

had this on my mk2 gti last month, changed thermostate stil the same, removed heater matrix filled it with hot water and even though it was not blocked when i flushed it only a third of it was warming, hope this is not the problem as it was a pig to change on the mk2, 

[CarlW]

Do you have a  part number for the mk5 heater matrix by any chance? Just so I can find out how much it may cost of this is the problem I have. Going to take it to a garage this afternoon to see what he says.

Thanks,
Carl.

[r5gtt]

If the heating is fine blowing hot air out the cheapest option to start with is the temp sensor as these are prone to failure.

I doubt it's your matrix unless you've got contamination in there of some sort. eg mixing different coolant.

M

[Takumi]

depending if tranismission is DSG or manual,there are more little termostats. Had same issues and it took awhile after i got a look at ETKA. 1 little thermostat is in the line where cooling for turbo goes. Other on the cooling line going to DSG/trasmission.

Seems there are forum users, who have done this. Have you tried searching?
http://www.mk5golfgti.co.uk/forum/index.php?topic=78341.0

[r5gtt]

Oh yes,  the two inline thermostats on our dsg models. I'd recommend all three done at the same time then you can't go wrong which is what I'll be doing once the weather gets warmer as I'm in no rush atm 

[CarlW]

Mines manual

[r5gtt]

@CarlW less work or labour involve then