E30 Zone

Hi guys, my 316i m40 is overheating over the last few days,im thinking theres an airlock in the cooling system but how can i free it?? any ideas??

Unless you have recently drained and refilled the cooling system, it's not an airlock.
What are the FULL symptoms of your problem?

could be viscous clutch (not sure if M40 has this), thermostat, all sorts. As Brian says, need more info....

I Changed the thermostat about 1 month ago so yes the cooling system has been drained and refilled.This also happened 6 months ago when i changed the cam belt as i had to take rad out to get at belt but anyway she's still overheating,when driving slow or fast she still overheats,turned the heating on and sometimes it blows out cold air and sometimes hot air but its blowing out hot air at the moment,when she blows out cold air she tends to overheat that being the heater control turned to full heat

Have you tried to bleed the coolant system from the bleed screw?

yes tried bleeding from the bleed screw and nothing came out the nut was completely dry

Sounds like it needs topping up and more bleeding. What's the level like in the expansion tank?
Someone else would probably be better to give the particular procedure than me.
I've managed it not too long ago--something with having the heater controls at the right setting and continue topping up (whilst running) until there's liquid running all the way around. I'd have to look it up again to be certain. Parking with the nose up a slope helps (puts the gas vent at the high point--gases such as air tend to rise in fluid such as water/coolant).
(I also did a quick thrash round the block to dislodge any bubbles, but be careful not to overheat it doing this--not officially recommended!!)

try pulling a plug lead off???
should run at 3/4 on the guage then. also doubles the bhp! improves the mpg by 1/4. and get admiering glances from the people having to follow you at 20mph.

lloydp wrote:gases such as air tend to rise in fluid such as water/coolant.

Fill the coolant bottle to the top, loosen the hose clip on the pipe that goes to the top heater stub pipe on the bulkhead, pull it off, just clear of the stub, so that any air in there can come out along with some coolant. Push the hose back on and tighten the clip.
This will have cleared the airlock, but if it happens again, you have a head gasket problem, with combustion gasses getting into the coolant jacket.

im in a very similar boat....changed radiator as it was leaking, now she will run fine for a long while, however after being stuck in traffic for some time she will boil over....coolant is bled fine with a hot heater etc...strongly suspecting HG..new engine excuse time!

JungleGus wrote:im in a very similar boat....changed radiator as it was leaking, now she will run fine for a long while, however after being stuck in traffic for some time she will boil over....coolant is bled fine with a hot heater etc...strongly suspecting HG..new engine excuse time!

Change the viscous fan coupling ASAP, or you soon will have a head gasket problem!

if all that fails take the water pump out and have a look to see if the blades are fixed properly on it i had this problem before it would dlow hot and cold didnt think it would be the water pump as it was brand new but took it out and the blades where just spinning on the shaft

she seems fine now over the past 24hrs temp gauge is below half,blowing out hot air,do i still need to change viscous coupling?she did seem to use alot of water but now is fine,so wat was the problem,cos alll i did was fill up expansion tank and primed top hose

Aido wrote:she seems fine now over the past 24hrs temp gauge is below half,blowing out hot air,do i still need to change viscous coupling?she did seem to use alot of water but now is fine,so wat was the problem,cos alll i did was fill up expansion tank and primed top hose

The problem seems to have been incorrect filling and bleeding procedure after the cooling system was drained.
You won't need to change the viscous coupling unless the temperature gauge moves towards the red sector when travelling slowly or stopped with the engine running.