A4 Coolant Bleeding

Hello, i replaced my temp sender today on my 1.9tdi 90bhp, not thinking it would suddenly gush out all of my cars coolant...woops

I basically want to know how to bleed the system, i've put in about 3 litres of water/antifreeze mix, and cant get anymore in, initially it started slowly draining in with air bubbles being released. I then ran the car around for a bit and it doesn't exceed 90degrees, and the coolant level hasn't changed, so does that mean its ok and its self bleeding? or is there a procedure, everything i read doesn't seem to answer my question very well.

Also, what is this g12 coolant? do i really need to use it?

I need to know fairly quickly, as i would like to use the car this evening!

Thanks, Paul

in the centre of hte bulkhead just below screen level there are two coolant pipes that enter through the bulkhead to the heater matrix. undo/loosen the clip from one of these (sorry i forget which) and partially slide the pipe off the stub of heater matrix. before the pipe comes off completely you should see a small (circa 2mm dia) hole.

as you fill the system, keep squeezing all the flexible pipes in the circuit to dislodge any trapped air, as fluid begins to flow from the bleed hole on the stub, loosen the clip again and slide the pipe back onto the stub, and tighten the clip.

there is a bleed hole on one of the pipes to the heater (near the ecu). you have to undo this pipe and half pull it off so that water can escape through the hole. warm the engine up fully and when water starts to come out the bleed hole put the pipe back on quickly.

it is also a good idea to remove the header tank and lift it as high as you can with the pipes still connected (best to have someone else holding it up and filling while you look after the bleed hole). once the heater pipe is back on and secured, refit the header tank and fill as necessary.

this should ensure that you have no air locks as the heater pipe is the highest part of the system, and the idea behind lifting the header tank is to get it higher than the bleed hole.

ha ha beat me to it darkhorse

i missed the tip about the header tank though, so its all good.

Wow, thanks alot you guys i will go try it now :)

has anybody a clue as to what coolant i can use? i've seen alot of people refer to g12 but i'm not sure if i really need it? i don't want to bust any seals using incorrect fluid

i think the only stuff you'll get away with is either g11 or g12, and i think audi have stopped the g11 stuff (although i might be wrong here)

what i do know is that getting the right stufff from audi is strongly advised as if you put any old stuff from halfords in you risk turning the glycol to jelly (literally) and clogging up the whole system.

buying straight from audi will only cost a fraction more anyway.

Ok i will get some asap, however that leaves me stuck for the weekend...so will it be ok to run with regular antifreeze for the weekend? then a full flush out of the system along with fresh g12?

I bled the system, it all seems fine, heater works as normal and my temp gauge sticks to 90. I only put in approx 3-4 litres, and i seem to remember it having a 6-7litre system, so either its not full or there was some g12 still in there somewhere?

Thanks alot for your help so far, i'm very grateful

i wouldn't like to say it would be ok to mix them even for a short period of time as i don't know how long it would take for the reaction that turns it to jelly to take place (although as a rule of thumb adding heat to a chemical reaction only makes it faster), i'd say you're better off running a more diluted g12 fluid mix (ie just fill up with as much water as is needed) than risking putting any generic antifreeze in.

as for how much the system holds in total i couldn't say for sure. and whats left in the system will depend on where you drained it from? to get the system totally empty i'd drain from the thermostat housing as this is where the two coolant paths converge, draining from anywhere else means you may fully drain only one part of the system.

just re-read the first post, if you drained from temp sender position there will still be alot of coolant left in the system, not a bad thing if you a temporarily running a diluted mix...