Overheating M40 engine in traffic * NEARLY FIXED! *

[Ritz]

My daily driver has recently started to overheat in traffic after a good run. Temp gauge creeps v.close to red zone.

Have already replaced the viscous fan coupling but turns out that wasn't at fault. I stopped the car when it was overheating today and the viscous fan coupling stopped when I stuck a newspaper in the fan blades.

Turned the car off and put my hand close to the rad and it was cold! Could hear faint bubbling noise in engine bay too.

Water pump? Seems coolant not going through rad?

Thanks in advance.

[bss325i]

You should not be able to stop the viscous from turning when its hot. It should be engaged when hot.

[Brianmoooore]

Does the heater work properly? If it does, then I doubt if the pump is at fault.
More likely to be the thermostat.

[Brianmoooore]

You should not be able to stop the viscous from turning when its hot. It should be engaged when hot.

If the rad is cold, the viscous won't know that the car's overheating.

[Ritz]

You should not be able to stop the viscous from turning when its hot. It should be engaged when hot.

Yeah thats what I assumed so turns out the original coupling was fine. I fitted a new one few weeks ago and today I managed to stop it when the engine was hot. So clearly the rad isn't getting hot enough for the coupling to kick in.

[Ritz]

Does the heater work properly? If it does, then I doubt if the pump is at fault.
More likely to be the thermostat.

Heater does blow warm at full hot position. Never hot as before...

Looks like possibly thermostat next on my list...

[Brianmoooore]

If the heater performance is down, in spite of the engine being hotter than normal, then you may be right the first time. BMW M40 water pumps don't normally give trouble, apart from bearing failure and consequent leakage (or the other way around), but yours could have some poor quality aftermarket part fitted!

[bss325i]

You should not be able to stop the viscous from turning when its hot. It should be engaged when hot.

If the rad is cold, the viscous won't know that the car's overheating.

didn't read the bit about the rad being cold.

[Ritz]

If the heater performance is down, in spite of the engine being hotter than normal, then you may be right the first time.

Yeah I had the odd occasion on the motorway when it blew cool air in the fully hot position

BMW M40 water pumps don't normally give trouble, apart from bearing failure and consequent leakage (or the other way around), but yours could have some poor quality aftermarket part fitted!

Could well be true, the car has had 9 previous owners.
Do you think fitting a new BMW water pump AND thermostat at same time is a wise step?

[Ritz]

You should not be able to stop the viscous from turning when its hot. It should be engaged when hot.

If the rad is cold, the viscous won't know that the car's overheating.

didn't read the bit about the rad being cold.

Forgiven Barry lol

[Alex]

i'am having a similar problem my heater does not work even when the temp guage was above the 3/4 position once moving it goes back to the center, ive orderd a new viscous but the heater wont blow hot at all, it was a bit temprimental at first, blowing hot after a good 10 mins after car is at fully operating temp but now has packed in completely. when in traffic the other day on the a66 my temp guage was just about to go into the red so i put the heater to hot and speed 4 to try and cool the engine down but nothing but cold air

i checked my carpets and there not damp so hopefully nothing is leaking

[Brianmoooore]

Regarding the heater; another scenario is that the head gasket is beginning to fail at the back of the head, and combustion gasses in the coolant are causing partial airlocks.

[Alex]

thats what i was thinking, prehaps when it has overheated its wrecked the head gasket

[mr_dink]

thats what i was thinking, prehaps when it has overheated its wrecked the head gasket

OP hasn't mentioned overheating so a new thermostat and water pump should get it sorted.

Alex hate to say this but your problem sounds like the profile gasket..... How many miles is yours on and do you have any record of the profile gasket being changed?

[Alex]

thats what i was thinking, prehaps when it has overheated its wrecked the head gasket

OP hasn't mentioned overheating so a new thermostat and water pump should get it sorted.

Alex hate to say this but your problem sounds like the profile gasket..... How many miles is yours on and do you have any record of the profile gasket being changed?

133k and has proof of a top end rebuild with profile gasket done at the same time Cost £600 mileage 70k done in 2000

car still drives fine just overheats in traffic and heater no longer working

[Alex]

regarding what brain said, if the head gasket did go is it possible that bits could end up floating in the expansion tank as there is something bobbing around in there, i changed the coolant about month ago , i cannot really tell what it is as some silly previous owner thought it would be a good idea to paint the expansion tank black

[Ritz]

Just did a closer inspection today, the lower half of the rad is only warm when needle shows halfway, also the rad bottom hose (from thermostat housing) is warm but not hot.

Rad top hose hot and fairly hard as usual. I did top up coolant and water again which has helped a little. I also notice the coolant in the radiator expansion tank goes right down to the bottom and doesn't stay in the middle when cold (as indicated by the marking that says "COLD" "KALT" etc)

Any ideas?

[Ritz]

Ok. Replaced the thermostat this morning (thanks to Chris W for the part!).

Had trouble getting the water pump pulley off, damn nuts too tight! I could not get any force to undo them at all, any tips?

At this point I tried refilling coolant and starting it up. Let it run, thermostat opens properly but radiator still cold despite both left/right rad hoses hot and firm. And hence viscous coupling not kicking in due to being cold...

Looking like water pump at this stage unless anyone has other ideas? Anymore tips for getting the water pump pulley off? Have tried holding one nut with spanner then tried to undo other nut with same size spanner, no good.

[Brianmoooore]

Had trouble getting the water pump pulley off, damn nuts too tight! I could not get any force to undo them at all, any tips?

Put the fan belt back on. Tight.

[Ritz]

Put the fan belt back on. Tight.

Might try that. But I even put two spanners in, one holding one nut, the other trying to undo nut opposite?

Everything is back in place, I will need to dismantle again. Trouble is I need the car next couple of days. Am I risking a lot by driving it more until I get it fixed?

[Ilkorin]

Sounds exactly like a problem I had with my old car, turned out the water pump had failed...

if the hoses are getting really hot and the rad is warm only very close to the hoses, it's likely there is no flow through the system... the bottom hose attached to the thermostat will also be hot if it's the pump and not so hot if it's the thermostat.

summary: water pump is dead

If you've got a new pump, a quick thwack with a hammer on the spanner gets those water pump bolts off quite effectively....but use that as a last resort because you could shear a bolt...

[Ritz]

summary: water pump is dead

If you've got a new pump, a quick thwack with a hammer on the spanner gets those water pump bolts off quite effectively....but use that as a last resort because you could shear a bolt...

I have a good second hand water pump, just a matter of getting those nuts off now. The pulley nuts are my first problem, I guess I will have to see what the water pump nuts are like.

Thanks for tip

[Ritz]

Right, managed to get the pulley nuts off and eventually the old water pump. Fitted newer water pump, refilled the coolant and put everything back together, still overheating, needle getting into the red zone now...

Is there an air lock? I did undo the bleed screw at the top of the rad for a while before I saw steam come out. Rad hose from thermostat housing cold, and rad top hose warmish not getting hard.

Thermostat needle gets halfway and then into red very quickly.

Only thing I haven't changed is the radiator. Unless I am still missing something or I have screwed up somewhere during fixing the whole problem...now I'm clueless. Left the car too cool overnight, will try in the morning.

Any other ideas folks?

[Ritz]

Had trouble getting the water pump pulley off, damn nuts too tight! I could not get any force to undo them at all, any tips?

Put the fan belt back on. Tight.

Worked a treat Brian, thank you Sir!

[Brianmoooore]

Heater working?

[Ritz]

Heater working?

Only thing I haven't tried yet. What can I expect? What should I expect? My radiator is still cold too....

[mr_dink]

What procedure are you using to fill and bleed the system?

Possibly the rad isn't getting hot because there's no water in there?

You need to remove the bleed screw in the rad completely and keep filling until water comes out the hole and the bubbles stop.

[Ritz]

What procedure are you using to fill and bleed the system?

Possibly the rad isn't getting hot because there's no water in there?

You need to remove the bleed screw in the rad completely and keep filling until water comes out the hole and the bubbles stop.

Bled by removing rad bleed screw at bottom of the rad expansion tank.....and hose coming out of thermostat housing. I think I will bleed the whole system again in the morning and refill. Bound to be airlock somewhere too?

[Brianmoooore]

Bled by removing rad bleed screw at bottom of the rad expansion tank

Eh! That's the drain tap!!

[Ritz]

Bled by removing rad bleed screw at bottom of the rad expansion tank

Eh! That's the drain tap!!

I'm starting from scratch tomorrow morning. I think I'm loosing it!

Drain all coolant again, refill again and see what happens.

[ShakeyC]

Take your time and refill slowly, run the engine with only the expansion cap off and top it up as needed. Air will gulp itself out with few dabs of throttle and turn heater temp dial up and down to help bleed air out the heater matrix too.

[Brianmoooore]

Keep the heater temp dial at full hot, fan on position 2, top two sliders fully to the left, and the bottom slider fully to the right.
Monitor the heat coming from the floor outlets, and if noticeable heat doesn't appear after about a minute from cold, then you probably have an airlock.

[Mr_Dee]

Yeah this seems to be a common problem, but I have just lived with it for the past 2 years lol, but I am determined to get to the bottom of it after reading this thread, I have a 320i and it was always fine in the way of temperature, and it was while i was doing some work on it, car was stationary and engine off, I moved the fanbelt round by hand and heard some bubbling, and ever since then the car overheats in traffic, as I sit there the temp steadily goes up to the red, i put the heater on hot and max speed blower and that cools it back down, is just damn annoying in the summer ! lol, I have tried bleeding it more times than I care to mention (by the book), changed the viscous fan, thermostat, but am now thinking of fitting an electric fan, dont know, nightmare

[Brianmoooore]

E30's, in the UK climate, have masses of spare cooling capacity. Your car is faulty, and bodging in some electric fan won't help!
A car's cooling system only needs bleeding once (if done properly) - if it needs bleeding on a regular basis, then either the head gasket is leaking, or the small hose from the radiator to the coolant tank is blocked.
A replacement viscous coupling may be dud if it wasn't stored properly, or your water pump, if a cheap aftermarket version, may have rotor problems.
Radiators don't last forever either, but this isn't likely to be your problem if it doesn't overheat under load.

[Mr_Dee]

Yeah I know there is something wrong with it, just havent fathomed it out as yet, no it doesnt need bleeding on a regular basis sorry, I have only tried to bleed it on various occasions incase its got an air block causing the problem and maybe I hadnt bled it properley the past times, but I have done it by the book