cooling system header tank

ChrisG · 17-02-09, 10:44 AM

This is for my 1985 80 Sport. OK other than a good cleanout and flush I have done all the bits on this, BUT the low water light now flashes continuously.
It should flash when the ignition comes on, then go out unless the coolant level is low when it flashes ( I understand it also flashes if the temperature is very high but as I have a working guage I can see that it is not that.)
Fan cuts in and out as it should.

I suspect the sender in the bottle may have broken ( but was OK before I started draing down , rinsing, new stat etc)

The plug underneath the bottle appears to be designed to unscrew but doesn't.
Any ideas how it comes out?
Is the sender replaceable even?
Otherwise anybody have a working spare
857 121 407
857 121 403
443 121 403
are the part numbers on the bottle.
I suspect this may be used on a range of Audis ( and what's with the 443 number ? )
Thanks !

I've also asked on Audifans.

Guys get out your power steering details as I'm changing the fluid next !!

mikes2 · 17-02-09, 10:55 AM

got a spare tank with no sender but there's no threads on it.

I had something similar on my quattro after refilling the system - the low water warning would flash instantly.

I topped up with more G12+ and left it 24 hrs and it recovered and it's been fine since. Double check the plug isn't loose

ChrisG · 17-02-09, 11:07 AM

OK, I'll recheck the plug later
It's sat overnight, currently SORN so I cannot take it out for a run to check it out, just sitting outside the garage idling away is not quite the same !

Thanks Mikes2

Martc · 17-02-09, 11:11 AM

Did you do this to ensure you don't have an airlock?

Slide the heater colntrol to hot.

Remove the bleed screw from the top of the radiator.

Remove the 3 screws holding the expansion tank and lift it up as far as the hoses will allow whilst topping it up until coolant flows out through the bleed hole in the rad.

Replace bleed screw

Lower and replace expansion tank.

ChrisG · 17-02-09, 11:27 AM

done the heater thing, it's a DZ engine and no rad bleed but loosened the block temp sender, no air.
Not done the header bottle thing but shouldn't need to with no air in system??
Can but try !
Thanks.

Martc · 17-02-09, 12:26 PM

The reason you lift up the header tank is because its at the same height as the bleed screw, so you need the added height to push the air out of the system.The purpose of the bleed screw at the top is to ensure there is no air trapped at the top of the engine block. Not sure if the DZ had a bleed screw on its original radiator (again I don't know if you have an original rad either which may not have one)

How far down the block is the temp sensor, if its way down the block then you could have air in there?

ChrisG · 17-02-09, 01:22 PM

Yes I understand the physics !!
Original rad replaced three years ago, no bleed on the new one ( I'll check the old one as I kept it even though it leaked.... yes sad - but you never know when a pattern is required.... how sad !! )
The temp sender ( works the guage ) is almost the highest part of the engine, alongside the rocker cover.

vag80 · 17-02-09, 07:22 PM

Are all the hoses and rad hot to touch? My 80 took ages to bleed through as it has no bleed screw.
I loosened the bottom hose and pumped the to hose which helped pump the coolant round and also put heater on hot and held the revs at 2500rpm

vag80 · 20-02-09, 10:44 PM

Chris did you sort out your coolant problem

ChrisG · 21-02-09, 10:09 AM

yes and no !
I suspected the thermostat( new ! ) may have been faulty so I put back the old one, the guage then sat in the middle ( usual position) and fan cut in and out.
I took off the bottle to try and see if the sender was OK etc etc and of course there is then coolant loss so I topped it up ( about a litre) and ..... the guage goes off the top and fan doesn't cut in ( as rad seems cool )
Reckon there must be air trapped somewhere.
Interestingly this months Car Mechanics tested pressure drainer/fillers ( Sealy was best buy) as they say there are often problems and well worth using one............ I've never had any before in 25 years. arrgghh !
I need to get the technique as I wish to descale and then degrease system, each time will need a refill, then I can add new antifreeze and forget for a few years !

17-02-09, 10:55 AM	#2
mikes2 4 ring whore! Classic Audi Club Member Join Date: Nov 2007 Location: Polmont Posts: 2,617	got a spare tank with no sender but there's no threads on it. I had something similar on my quattro after refilling the system - the low water warning would flash instantly. I topped up with more G12+ and left it 24 hrs and it recovered and it's been fine since. Double check the plug isn't loose __________________ 1991 90 quattro 20v sport 1991 90 quattro

17-02-09, 11:11 AM	#4
Martc Black Coupe Collector Classic Audi Club Member Join Date: Feb 2008 Location: Towcestershiresheer Posts: 2,934	Did you do this to ensure you don't have an airlock? Slide the heater colntrol to hot. Remove the bleed screw from the top of the radiator. Remove the 3 screws holding the expansion tank and lift it up as far as the hoses will allow whilst topping it up until coolant flows out through the bleed hole in the rad. Replace bleed screw Lower and replace expansion tank. __________________ 95 UrS6 87 Coupe Quattro

17-02-09, 12:26 PM	#6
Martc Black Coupe Collector Classic Audi Club Member Join Date: Feb 2008 Location: Towcestershiresheer Posts: 2,934	The reason you lift up the header tank is because its at the same height as the bleed screw, so you need the added height to push the air out of the system.The purpose of the bleed screw at the top is to ensure there is no air trapped at the top of the engine block. Not sure if the DZ had a bleed screw on its original radiator (again I don't know if you have an original rad either which may not have one) How far down the block is the temp sensor, if its way down the block then you could have air in there? __________________ 95 UrS6 87 Coupe Quattro

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17-02-09, 11:07 AM	#3
ChrisG Senior Member Classic Audi Club Member Join Date: Dec 2007 Location: Bracknell, Berks. Posts: 1,465	OK, I'll recheck the plug later It's sat overnight, currently SORN so I cannot take it out for a run to check it out, just sitting outside the garage idling away is not quite the same ! Thanks Mikes2

17-02-09, 11:27 AM	#5
ChrisG Senior Member Classic Audi Club Member Join Date: Dec 2007 Location: Bracknell, Berks. Posts: 1,465	done the heater thing, it's a DZ engine and no rad bleed but loosened the block temp sender, no air. Not done the header bottle thing but shouldn't need to with no air in system?? Can but try ! Thanks.

17-02-09, 01:22 PM	#7
ChrisG Senior Member Classic Audi Club Member Join Date: Dec 2007 Location: Bracknell, Berks. Posts: 1,465	Yes I understand the physics !! Original rad replaced three years ago, no bleed on the new one ( I'll check the old one as I kept it even though it leaked.... yes sad - but you never know when a pattern is required.... how sad !! ) The temp sender ( works the guage ) is almost the highest part of the engine, alongside the rocker cover.

17-02-09, 07:22 PM	#8
vag80 Senior Member Classic Audi Club Member Join Date: Oct 2008 Location: Bracknell Posts: 1,967	Are all the hoses and rad hot to touch? My 80 took ages to bleed through as it has no bleed screw. I loosened the bottom hose and pumped the to hose which helped pump the coolant round and also put heater on hot and held the revs at 2500rpm

20-02-09, 10:44 PM	#9
vag80 Senior Member Classic Audi Club Member Join Date: Oct 2008 Location: Bracknell Posts: 1,967	Chris did you sort out your coolant problem

21-02-09, 10:09 AM	#10
ChrisG Senior Member Classic Audi Club Member Join Date: Dec 2007 Location: Bracknell, Berks. Posts: 1,465	yes and no ! I suspected the thermostat( new ! ) may have been faulty so I put back the old one, the guage then sat in the middle ( usual position) and fan cut in and out. I took off the bottle to try and see if the sender was OK etc etc and of course there is then coolant loss so I topped it up ( about a litre) and ..... the guage goes off the top and fan doesn't cut in ( as rad seems cool ) Reckon there must be air trapped somewhere. Interestingly this months Car Mechanics tested pressure drainer/fillers ( Sealy was best buy) as they say there are often problems and well worth using one............ I've never had any before in 25 years. arrgghh ! I need to get the technique as I wish to descale and then degrease system, each time will need a refill, then I can add new antifreeze and forget for a few years !