E34 540 cooling problem

[The T Boy]

A month ago the top radiator hose blew off after I had been stuck in heavy traffic for about half an hour. Assuming that it was just a poorly tightened clip I reattached the hose to the radiator outlet, tightened the clip right up and refilled the system.

All was well until this morning when, stuck in the mother of all tailbacks for half an hour, the hose ceremoniously detached itself in another explosion of steam.

I've reattached it and tightened it up again but there must be something else causing this to happen. I can understand pressure building up as the temperature rises but thought that should be normal and the system should cope. There can't be a major problem with the cooling system as if there was then surely the problem would occur if stationary for 5 minutes or so.

Does anyone have any ideas about what could be wrong?

T

[mmm-five]

There's a few things that could cause this...

1) Reduced capacity of hoses due to build up of sludge/silt on hose walls (due to not flushing the system and using tap water instead of distilled water)

2) Silt & sludge in valves, pumps, etc (check water pump, aux water pump and heater valves for blockages/damage)

3) Pusher fan (in front of radiator) not working, missing, etc.

[The T Boy]

The cooling fans seem to be working fine so I guess a full system flush and desludge is on the cards.

How does this work to actually reduce the pressure in the system? I'm not doubting your advice - just like to understand the cause and effect of such problems for future use.

T

[The old fella]

make sure you are getting a good flow of coolant around the system,
the coolant tank has a small inlet pipe just below the cap,this is the return (and bleed) for the rad,
These can block up and prevent a good flow back into the tank.

Also when you refill the car with coolant, switch the heater on to full and run the engine at around 3-4000 revs until the heater system is blowing hot, that takes all of the air out of the heater system.

You didn't mention if the temp gauge was showing hot?

Another thing, the necks of the rad top hoses have a nasty habit of breaking of leaving only about 1-1.5 cm
of neck to clamp your hose to, Its not enough to hold the hose securely.

Graham

[The T Boy]

The temp gauge just started to move past the middle point when it went pop this time but was in the middle last time. Normally the gauge gets to the middle and stays put, it never runs above this which is why I don't think there is a general problem with the system.

Maybe the problem is the heater then as it never blows really hot through the floor vents. The face vent you can turn up and it gets hot as do the window ones. At first I thought this lack of real heat was a problem but then read the manual and other opinions on the web which indicated that the heating system regulated the cabin temperature rather than just heating it up. I thought that explained why the fans never seemed to blow red hot air out but the post above indicates that at full setting they should be blowing hot.

Does the return / bleed hose get blocked just at the filler tank end or do both ends need checking?

T

[mmm-five]

The T Boy said:

The cooling fans seem to be working fine so I guess a full system flush and desludge is on the cards.

How does this work to actually reduce the pressure in the system? I'm not doubting your advice - just like to understand the cause and effect of such problems for future use.

T

As the temp rises, the prssure will increase, and eventually something gives.

In each of these cases it's the reduced flow that equals higher temp, which gives higher pressure.

[The T Boy]

mmm-five said:

As the temp rises, the prssure will increase, and eventually something gives.

In each of these cases it's the reduced flow that equals higher temp, which gives higher pressure.

Thanks So provided the temp stays in the normal range there will never be enough pressure to blow the hose off. This makes a lot of sense.

I was worried that for some random reason my cooling system was creating too much pressure.

[mmm-five]

The T Boy said:

mmm-five said:

As the temp rises, the prssure will increase, and eventually something gives.

In each of these cases it's the reduced flow that equals higher temp, which gives higher pressure.

Thanks So provided the temp stays in the normal range there will never be enough pressure to blow the hose off. This makes a lot of sense.

I was worried that for some random reason my cooling system was creating too much pressure.

Assuming the thermostat/temp gauge is reporting the temp properly.

[Talkwrench]

May be worth checking/replacing the expansion tank cap. There was a recall on a lot of BMW's around that time due to the wrong pressure cap being fitted. It usually ends up blowing the expansion tank or deforming the radiator when the engine gets too hot. Its just a thought - and worth checking.

[B'stard Child]

I wouldn't trust the guage to indicate anything at all - if the dash is anything like my 740 and middle of the guage is reached at 80 Deg C and the temp on the OBC keeps going till it sits at 112-114 deg C

I was horried that it runs so hot but on researching the subject it is quite normal

What I wouldn't trust the guage to do is indicate if it's running hotter than it should as it just apears to be a display based on a timer from a cold start rather than any real temp indicator

JM2pW

Edited by B'stard Child on Wednesday 9th January 20:24

[The T Boy]

Well I took the top hose off and the radiator neck has broken off leaving only about an inch left. The break is clean and the broken bit is still inside the hose so I didn't notice that anything was wrong when I originally reattached it.

It looks worryingly like the neck is an integral part of the radiator though so presumably that means I need a whole new one. Nice.

I'll also get onto BMW tomorrow to find out whether I've got the right filler cap then have a desludging session at the weekend.

Thanks for all the advice.

T

[Talkwrench]

The T Boy said:

Well I took the top hose off and the radiator neck has broken off leaving only about an inch left. The break is clean and the broken bit is still inside the hose so I didn't notice that anything was wrong when I originally reattached it.

It looks worryingly like the neck is an integral part of the radiator though so presumably that means I need a whole new one. Nice.

I'll also get onto BMW tomorrow to find out whether I've got the right filler cap then have a desludging session at the weekend.

Thanks for all the advice.

T

A very common weakness in the radiator top hose connector, Im afraid!
The engines are not particularly prone to sludging up so a good flush should shift any silt that is present. A new rad will obviously be nice and clean.
Don't go near BMW for a radiator by the way. My local radiator specialist (Northern Radiators) is quoting around £120 for a new Behr radiator.

[The T Boy]

I dread to think what BMW would charge. £95+VAT from Swedish and French so the cost isn't too bad.

Anyone know whether the radiator will slide out easily or is it a front-off job?

[Talkwrench]

Easy, slide out job!

[The T Boy]

Talkwrench said:

Easy, slide out job!

You've now idea how much this has cheered me up. : I had visions of my car in pieces on the garage floor for 3 weeks with the missus constantly asking why this 2 hour job was taking so long.

[The old fella]

Normally the blockage is in the expansion tank, When you have fitted the rad and bled all the air that you can Pull the return pipe off of the tank and make sure you have a nice flow of coolant.
Then put it back on to make sure the coolant is flowing into the tank, it's a very common prob for these to block up.
Graham