Help! How do I bleed the coolant system?

[Cheapskate]

My car very nearly overheated today and when I stopped, the expansion tank looked like it was boiling and had overflowed. I've read about bleeding the coolant system to remove airlocks, but don't know how this is done.

Please tell me, I've got another 60 mile commute in the old girl tomorrow morning and the temperature gauge went off the scale today, I had to pull over and shut her off.

 

[Dusk]

Sounds like it might be blocked?

 

[bobbybok]

To bleed the air you must take the top off the header tank and run the engine with the heater on full blast till the cooling fan cuts in, this should push all the air out of the system and then put the cap back on, thats the way I do it anyway! Must say though this would only need to be done if the coolant has just been replaced, if the engine has started cooking out of the blue it maybe a bigger problem eg blown head gasket.

 

[sonic]

are you sure the thermostat hasn't seized shut, are the top and bottom hoses getting hot?

 

[Cheapskate]

This overheating is following a coolant change 200 miles ago. The thermostat seemed fine but I changed it anyways. I've only done about 300 miles in the car since I got it seems that its overheated during the previous owners time with the car, there were white deposits on the underside of the bonnet above the rad cap.

I get a gurgling noise from the heater matrix at the moment, and its had that gurgling noise throughout my short ownership. I've flushed the whole system twice now.

 

[bobbybok]

sounds more serious than trapped air! Heater matrix or head gasket.....wounder!!!

 

[Zephyr]

simiar what has been said but in my words...
1 - open radiator cap while engine is cool/cold NOT HOT WARNING else its gonna explode in ur face n u WILL GET BURNED!
2 - most likely u over heating cuz no water in engine u can c if the water is there or not if its not fill it up to top check coolant level then start engine
3 - turn on heat full fan on full n pay attention to c if it goes hot as it should
4 - let it run for abit dont need that long
5a - if its not over heating thats good
5b - if its over heating turn off b4 it gets worse
6 - turn it off
7 - is hot air blowing out? yes good if no then prob isnt enogh water in engine yet n check the radiator level again but again NOT when engine is roasting hot like i said it will explode but u can feel the top hose (hose leading into the radiator) if its getting warm or if its hot use it as a kinda indicator to how hot the water is
8 - most likely when u open cap again it look empty top it up to the rim again
9 - repeat until when u check cap the water level stays high n then that means u aint got air in no more but by this time u should get hot air blowing outta heater n temp stays in middle like it should but i would drive for day if i use car normally n it hopefully shouldnt over heat n then next morning check the level again

if doing this n it dont work u prob got a blockage or something worse but if so try this remove the bottom hose to radiator n then get like a hose n blast it down radiator to try get a blockage out if there is one then do what i said above n top it all up but after doing all this n it dont work then u prob got a serious problem n i say take it to a garage...
then let it cool down then its prob

 

[Cheapskate]

Right, it seems I've cured the overheating problem, by doing everything mentioned on here and more. The temperature is stable once more, but the expansion tank still bubbles after a drive, but its not overflowing now.

Does anyone else's expansion tank bubble?

 

[rlees85]

i dont think so, never noticed it, where does your temprature gauge rest when at normal running temprature? mines just a tiny bit under half-way round

 

[ollie240585]

Mines just under mid-point aswell

 

[Cheapskate]

Mines just under half way round as well now, but definitely bubbling. You can hear it from the drivers seat when you turn the engine off just bubbling away.