heater problems

[Dizzie]

driving round town the heaters are working fine. Once I get on the motorway or dual carriageway they go cold (buurrrr)

any ideas?

I'm going to check the coolent in a bit to rule that out. Other than that it's new matrix box time. 20 mins job for me to swap one

[Mk2Kezza]

Its not the bypass valves by any chance?
They are intended to stop the full flow of hot water from the engine passing through the matrix(As they can be a bit dodgy apparently). Maybe the water is warming up too hot, while driving on the motorway, the valve is closing too much and not allowing any water through at all? Sounds possible to me. Unless of course you've removed the valves already!

[rubjonny]

I'd say bypass valves too, it could also be low coolant

[Dizzie]

what am I looking for with this valve?
I have a mk3 matrix on the blue mk2 so I haven't got the bypass and the heaters are awesome on that.

[rubjonny]

follow the coolant hose going from the plastic flange on the right side of the block, if it has been cut and a metal valve fitted then you have the bypass valves fitted.  Replace the feed & return hoses with new uncut ones from GSF, about £8+vat each.  Or use a bit of copper tubing.

[Dizzie]

I think I know what you mean. There's a small hose going between the 2 hoses that goto the matrix. I shall block the small middle one and go from there.

[Organisys]

I think I know what you mean. There's a small hose going between the 2 hoses that goto the matrix. I shall block the small middle one and go from there.

That will still block the flow. take the valves out, and by pass them with a bit of pipe.

It's the high pressure due to water pump running at high revs , thats causing them to by-pass the matrix I think.
 

[wag,en,volks]

the heaters on my g60 dontwork at all is it gonna be the whole matrix needs swapping ? and if so whats entailed?

[AndytheGreek]

driving round town the heaters are working fine. Once I get on the motorway or dual carriageway they go cold (buurrrr)

mine too... 

[Ali]

My heater has not been working for a year since the AA touched my car!! I got a hole in my hose - they drained the system patched up the hose and never bleed the radiator!! Cowboys. I got it sorted properly and by someone who knows what they are doing but it has never worked again. No one seems to know what is wrong with it. I just had my coolant system looked at to get it throught the MOT still does not work - any suggestions?? I love my GTI, but I am no mechanic, so any suggestions can you put it in idiot language! Thanks.