Vw polo 1.4 1999 3dr hatchback 8V petrol. I had problems with my car a couple months ago, heater started to play up, kept loosing water and eventually had to change head gasket as water was mixing with oil. Now the heater is playing with my head lol, when I start the car , it’s quite ok because it warms up quick after a few minutes and when I turn the heater on it blows hot air, then after a minute or two it goes cold, then within seconds it goes cold then warm again, over and over same procedure (while the heater is on all the time) . Therefore, I checked the hoses, the two leading in and out of the radiator are dead hot! Therefore, it seems like its circulating, so I checked the two hoses that goes into the cars cabin, one hose (the top one) is hot but the bottom one is warm but not cold. I am thinking it might be the heater matrix maybe,cant really be the water pump or the thermostat? right? because the water is circulating. Where is the matrix located? Is it in the cabin behind the dash in the middle or under the bonnet? I don’t know whether to flush all the cooling system before I buy any parts or is it definitely the matrix? If not what else can it be? By the way if I buy any parts I’m gana flush it anyway because I need to put fresh antifreeze mix in it so I want to make sure what the real problem is so I don’t have to drain the system again I know it’s a pain to do it. Oh one more thing, I can’t find the drain screw for the radiator and there is no other cap except the reservoir cap for water + coolant? What is going on or is it me who can’t find it?

Thanks guys

:-D

I'm not all that familiar with the mk4, the matrix is going to be behind the dash board, it is probably slighty blocked/intermittantly blocking up, do the heater controls feel positive? if there abit sloppy it could be swithcing itself from hot to cold in the heater box.

the radiator might not have a drain screw, you may have to remove the bottom hose from it, as for the cap,it is the only one. the plastic cap is the pressure cap, vw use plastic caps and round plastic header tanks.

Are you sure that there is no air in the heater matrix? have you bled it?

It could be a partly blocked matrix, if you do flush it and that's as good a way to start sorting your problem as any, make sure that the heater control is in the 'hot' position, disconnect the two heater hoses and flush the matrix, first in one direction and then in the other. don't let the water pressure build up when you are flushing. or you could damage the matrix.

There isn't a drain plug, you need to disconnect the bottom hose. (use 'jubilee' clips' on all of the hoses when you put them back.

Whilst the bottom hose is off, you could also flush the rest of the cooling system. ( this can be helped by removing the thermostat)

Re-fill it through the expansion tank. As for anti-freeze, I would recommend that you use genuine VW G12 coolant, you mix this with water like any other, but it is longer lasting and kind to hoses and VW hoses aren't cheap.

well yea the heater controls feel ok like it did befor. yea i tried to find a drain plug for the radiator , no matter how much i looked i cudnt find any at all! haha. so i guess it is the usual hoses that connects to it that way. oh and i will try and flush the matrix on its own, thats a good idea thanks. but when I'm flushing the matrix on its own or the radiator , do i need to have the car running or it doesnt matter? if i just start to flush the radiator , wudnt the water go around the matrix itself too to get all the water out? i would of thought so cuz they both use the same water and coolant dont they? or is it a stupid thought and wont work? :oP

thanks for the help guys )

if you want to flush the heater matrix just disconnect the 2 hoses that go to the heater matrix from the thermostat housing, the hoses are quite tricky to get to though and you might need to take off the airbox, if you direct one of them into a large bucket, and into the other just squirt your garden hose into

although i must say in your case it's better to start with the basics, it probably only has some air trapped in the matrix.. to bleed it out find a slope to park the car on facing uphill, take the cap of the expansion tank and turn the heater to full, run the engine at idle and massage all the cooling pipes with your hands and it should purge the air from the system, there are no bleed screws or drain plugs in the cooling system at all

heater matrixhoses arrowed, the centre one(not arrowed) goes to the bottom of the expansion tank, large hose top left goes to top of radiator

Edited 12 August, 201016 yr by SkodaBoy

if you want to flush the heater matrix just disconnect the 2 hoses that go to the heater matrix from the thermostat housing, the hoses are quite tricky to get to though and you might need to take off the airbox, if you direct one of them into a large bucket, and into the other just squirt your garden hose into

although i must say in your case it's better to start with the basics, it probably only has some air trapped in the matrix.. to bleed it out find a slope to park the car on facing uphill, take the cap of the expansion tank and turn the heater to full, run the engine at idle and massage all the cooling pipes with your hands and it should purge the air from the system, there are no bleed screws or drain plugs in the cooling system at all

heater matrixhoses arrowed, the centre one(not arrowed) goes to the bottom of the expansion tank, large hose top left goes to top of radiator

yea i should try to get the air out first you are right, didnt think about it . good idea. thanks Skodaboy )

if you want to flush the heater matrix just disconnect the 2 hoses that go to the heater matrix from the thermostat housing, the hoses are quite tricky to get to though and you might need to take off the airbox, if you direct one of them into a large bucket, and into the other just squirt your garden hose into

although i must say in your case it's better to start with the basics, it probably only has some air trapped in the matrix.. to bleed it out find a slope to park the car on facing uphill, take the cap of the expansion tank and turn the heater to full, run the engine at idle and massage all the cooling pipes with your hands and it should purge the air from the system, there are no bleed screws or drain plugs in the cooling system at all

heater matrixhoses arrowed, the centre one(not arrowed) goes to the bottom of the expansion tank, large hose top left goes to top of radiator

iv tried massaging the hoses the way you described , did it for quite a while but it didnt work unfortunately. i even massaged the other hoses too but i dont think it made any difference. I'm gana try and flush the whole water system out really cuz its doing my headin and i want to get to the bottom of this as quick as i can cuz if its a major issue it should be sorted fast shudnt it. well as soon as i get some good weather cuz its been raining for the past few days here lol.

thanks for you are help )