Overheating and intermittent heaters :/ help please.

Hi all, basically I bought my discovery 300tdi at the start of the week, got it taxed and insured and drove it for the first time on Wednesday, just a short drive round no motorway ect.. All seemed fine apart from the heaters just blow cold.
Drove it to work on Thursday morning and going up the motorway at 70mph it started to overheat, whilst it started overheating the heaters blew hot air, I pulled over and let it cool down abit, set off again and it started overheating yet again as I was coming off the motorway but this time before I stopped it returned to the right temperature but still cold heaters, anyway I put a thermostat in it and tried to bleed it up, whilst bleeding it I found the heaters got boiling hot and all was fine until I notice water was slightly leaking out of the header tank cap, now every time I removed the top plastic bung from the thermostat housing nothing came about for around 30 seconds then a gush of water, as the water came out of the bung hole the header tank drained but when I put the bung back in the header tank refilled itself ???
I then put it down to the water pump so I drove the car home steady, on the motorway it never overheated and the heaters were boiling hot but as I left the motorway (around a 15minute drive) the heaters went back to freezing and the car started to over heat.
When I finally got it home I replaced the water pump and topped the system up again and attempted to bleed through, yet again wouldn't bleed, the water runs through all the pipes when I blow down the header tank but won't bleed through normally??
I have spent ages reading through threads and found a common fault to be the 'y' pipe from the header tank to radiator and thermostat housing, so back out I went and tried blowing down it and all 3 ends are clear so I am now really stuck and not sure what to do.
Can anyone shed any light at all on this problem please.

Trapped air in the heater matrix? maybe flushing that through might help...

I thought that too mate, I removed the pipe from the heater matrix and blew into the header tank, water then came through the pipe from the matrix BUT didn't when I just had it running, would it do that if it was slightly blocked maybe the block isn't too big to stop me from blowing it through but too big to stop the pump? If that makes sense

They can be right t**ts to bleed ! I know its going to sound stupid but try bleeding it with the front of the car raised so that all the air is forced out of the bleed screw and is not getting trapped in the heater matrix.If you still have trouble then i would try it with the thermostat removed and see if still overheats.

Leedscal said:

I thought that too mate, I removed the pipe from the heater matrix and blew into the header tank, water then came through the pipe from the matrix BUT didn't when I just had it running, would it do that if it was slightly blocked maybe the block isn't too big to stop me from blowing it through but too big to stop the pump? If that makes sense

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Have a go as colinl has suggested, if that fails flush out the heater matrix as they will easily trap air that is a pain to shift. Also if you fit a standard household radiator plug (size 1/2" BSP) to the thermostat housing you'll be able to bleed her whilst hot.

That's the weird thing though bud, I can remove the top bung when it's hot and nothing comes out for a few seconds :S should I remove the plug on the radiator when it's hot? Even though is says never remove when hot?

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Cheers bud, bought. Set

Pulling my hair out now tried every way to bleed it (apart from these bleed bungs I've ordered) it will not bleed up, I have taken the thermostat out and topped the water up all it does it spew the water out off the header tank, everything is leading me to suspect head gasket, except the fact that when I take the top bung out nothing comes out for ages, surely there should be pressure there??

Leedscal said:

I have taken the thermostat out and topped the water up all it does it spew the water out off the header tank,

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that is wot yu is doing wrong.

1) Top up coolant tank to correct level.
put cap back on.
2) remove radiator bung and fill to brim.
refit bung
3) remove thermostat bung and fill to brim.
refit bung.
4) run engine to circulate water.
stop engine allow to cool.

repeat 3 & 4 until yu get new bungs.

with new bungs, repeat above, but fit bleed bung in thermostat housing.
run engine till system hot and pressurised.
using screwdriver crack bleed nipple on bung until water comes out.

repeat daily until no air is ejected.

Just done that and took it out, running ok apart from no heaters, but if i go at 70ish it overheats but slow down to 40 and it cools down so im taking a guess at radiator??

rad or water pump

when it cools down go thru above routine again to check levels.

Will do bud, just fit a new water pump to it so hopefully its not a dud one.

Radiator ordered I really hope this works as I have thrown 300 quid at it in the last2 days but I do have a head gasket set too just incase but I can't really afford to have the car off the road for the few days it will take to get the head skimmed, at the minute I'm stuck between a rock and a hard place hence why I'm so stressed as you all can tell by my posts lol I appreciate all the help and advice I have received thanks all