engine o/heating , bottom rad pipe cold?

hi there all ,

PLEASE HELP ! ,

i had some serious overheating problems today and when i checked under the bonnet i had water bubbling in the system , water pipes were hard from pressure and noticed that the bottom rad hose was cold ? anyone know what this could be ?

thanks

i did have a leak......

water was boiling over and making pipes solid with air pressure , then few days later i noticed expansion tank crack but due to work and no time to fix it i just kept filling it up when low , fixed crack on the weekend , system was drianed and tank fixed but still getting same problems and noticed bottom hose was cold when engine was basicaly cooking , i think this was the cause for tank to crack under stress in the first place 

now thinking it could be water pump or thermostat or like you say it might just need a bleed ????

does anyone no which bleed screw i should open?

thanks again , cheers

bmw_lover wrote: i did have a leak...... water was boiling over and making pipes solid with air pressure , then few days later i noticed expansion tank crack but due to work and no time to fix it i just kept filling it up when low , fixed crack on the weekend , system was drianed and tank fixed but still getting same problems and noticed bottom hose was cold when engine was basicaly cooking , i think this was the cause for tank to crack under stress in the first place  now thinking it could be water pump or thermostat or like you say it might just need a bleed ???? does anyone no which bleed screw i should open? thanks again , cheers

I don't have much experience of working on BMWs, but usually, the first thing to check when overheating, apart from the obvious such as water levels, leaks and fan is coming on, is the the thermostat.  This is because it is usually easily accessible and secondly, cheap to replace.

I suggest that you drain the entire system and remove the thermostat.  Once this has been done, check the thermostat is working properly. 

Now the intention here isn't to find out whether the thermostat is serviceable or not, so that we can re-use it, rather the intention is to determine whether the thermostat is the cause of your problems so that we can discount everything else.

Place a garden hose in the various exposed hoses and flush them out with clean water.  Disconnect the bottom rad hose and flush out the rad as well.  Once you are satisfied that you've got all the grime out, start refitting the thermostat (make sure it is the correct one and that itopens at the right temp, this should be stamped on the base).

Mix the correct level of antifreeze with water.  this will not only raise the boiling point of the coolant, but also give you an idea of where leaks are coming from.

When pouring the water into the cooloant bottle/rad, do it slowly so as to avoid trapping air.  Once it's full, start the engine but keep the expansion cap off.  Keep an eye on the temps at all times, expecially top and bottom rad hoses. 

If you do encounter airlocks, you can use the bleed valves (if present), or just slightly disconnect the offending hose so that water runs out of it, to relase the air.

I think that is evrything.

One final thing is that, if your car is overheating in the way you descibe, you shouldn;t drive it until you've found the problm.  this is because only half of your engine is being cooled, whilst the other half wil bake slowly to death.

I have seen cylinder heads water channels literally melt, so mcuh so that the, it encroached into the cylinder chamber.  the engine literally bvecame a steam engine at that point!

Before you start replacing other items, you should make absolutely sure that there are no other air locks in the system.  Have you tried disconnecting the bottom hose and seeing if hot water runs through?

A worn water pump can cause this in theory, but I've never seen it happen before. 

You could replace the water pump and see how it helps, but whether you would want to depends on how easy it is to replace and the cost of doing so.

If it were me, and if after carrying out all the necessary checks, that would be my next move.

hi ,

today i left the old thermostat housing on (with old thermostat removed) then run a hose through the system in both directions , all was clear .

happy to see that rad was clear (loads a money).

then i fitted new thermostat (again) , topped up slowly with water + coolant till it came out of bleed screw and bled system for around 20 mins once warm squeezing hoses and using bleed screw to romove bubbles .

the rad and bottom hose were still cold at this point so thought i would leave to settle for a while then top up any coolant needed and take car out for a few miles to see if every thing ok.

temp was reading normal  and seemed ok , when i returned i thought it was ok BUT it was'nt.

engine was very hot along with top pipe , all pipes were solid with pressure , rad and bottom hose still cold ????????????????

the only thing i can now change is the water pump , if that dos'nt work then i will be very very puzzled , has i said in previous post rad and bottom hose were still cold even with thermostat missing (system clear) ?

many of you mention a airlock but its always rad and bottom hose that remain cold ??

could a water pump become so useless has to not sent coolant around system at all ?????

IM VERY CONFUSED , PLEASE HELP !!!!

if i bleed system for any longer it overheats real bad due to this problem

i also slowly filled system by disconecting top hose and filling till water came out where i disconected hose from making a complete cycle of water in system .

still same thing , boiling system , cold rad and bottom hose ????

hi ,

today i fitted a new water pump and tried bleeding system for a while but still need to bleed it some more tomorrow has i ran out of light.

i would just like to give you guys a run down of whats been done .

new thermostat

new water pump 

used hose to check if system clear of any blockages and water run freely through system ok

heating works ok

anyone know if rad should stay cold till thermostat opens ?

if rad and bottom hose still cold after a good bleed tomorrow i will be even more confused

wish me luck , i need it lol

ill let you know how i get on ! cheers