318i M40 Cooling issues...

Tue Dec 12, 2006 8:28 pm

Overheats at idle/standstill but fine at speed.

New Fan Coupling - still overheats.
New Water Pump - still overheats.
Endless coolant replacement and bleeding - still overheats.

I am now about to replace the thermostat and pray.

Questions:
1) Does the thermostat housing (not the thermostat) need a gasket when refitting?

2) If it's none of the above - why is it still overheating? Only thing left is radiator. Car is a 94 all original but not moving and it's starting to get a bit much. Any help at all is appreciated.

Tue Dec 12, 2006 8:40 pm

If it doesn't look like it's had a new rad it would certainly be my next move. In fact, it would be regardless.

Tue Dec 12, 2006 9:53 pm

i've just chainged my thermostat and ther was no gasket in hte box so at the most all you need is some instant gasket applied to the mating surface and it should be good til you need to replace it again.
on mine i had a bolckage just inside the thermo housing. hope this helps mate.

Tue Dec 12, 2006 10:38 pm

stitch-626 wrote:i've just chainged my thermostat and ther was no gasket in hte box so at the most all you need is some instant gasket applied to the mating surface and it should be good til you need to replace it again.
on mine i had a bolckage just inside the thermo housing. hope this helps mate.

IIRC, gasket on a M40 is an O ring, as is the water pump gasket as well.

Tue Dec 12, 2006 10:41 pm

He's right - unsurprisingly.

Tue Dec 12, 2006 11:33 pm

Brian, is that relevant to the thermostat 'housing' and not the thermostat itself as stitch-626 pointed out? I know there is an O-ring for the actual thermostat but does the housing mate to the block with some kind of gasket/sealant?

Also, if it's not the thermostat causing the grief after this, what would the next step - new rad as Chris-W suggests? Heater matrix? Flush all hoses?

Cheers all.

Tue Dec 12, 2006 11:52 pm

Just the O ring is all that's required.
E30 rads should be replaced at about 100,000 miles, but I would expect a scaled up rad to cause cooling problems under load rather than at idle.
Are you sure your viscous coupling is working, even if it is new? They can be damaged by incorrect storage.
Heater matrix won't be the problem - there's no flow through it anyway when the heater temp control is full cold.
Where does the temp gauge get to at idle? Can you hear the viscous lock up? Should really roar if you rev the engine when it's locked.

Wed Dec 13, 2006 7:22 pm

I switch the engine off before it get's to the red.

The fan coupling seems strong and visibly spins faster and harder than the tired old one - BWW OEM part too.

Just waiting on a set of those strange housing bolts that are threaded only at the very end to get it done.

The car has done over 100K, not sure if the rad has been changed. It has been topped up a lot with tap (hard?) water and not enough coolant additive I think and this shows in the form of limescale in some areas but not loads. I wonder if in the engine coolant channels there are areas narrow enough to trap it?

One clue - I did notice that coolant is NOT flowing from the top of the rad into the main hose feeding the engine.

But like I said, can't be the rad as it works fine when moving.

Thu Dec 14, 2006 8:11 am

I 'think' I have a spare rad, in pretty good condition, that I changed un-necessarily, that you could try out ?

I'm in N.W London area, so drop me a PM if you want to give that a go as well.

Wed Dec 20, 2006 3:28 pm

Cheers Bharat.

So I got everything sorted, put the new thermostat in, checked all the other new parts (Fan Coupling/Water Pump/Belts) are fitted properly etc.

Start the engine and the temp guage creeps slowly up between halfway and red after about 5 mins then kind of hangs there.
The heater is on full blast but no hot air coming through

very odd.

I went to bleed the coolant (again) and can see steam coming from the top of the rad area near the bleed screw but NOT the bleed screw itself

When I open the bleed screw, shit loads of steam comes out and just keeps coming out - no liquid.

Temp guage still at the same point - no hot air to the interior.

Am totally, utterly confused now as I've changed everything but the rad

Wed Dec 20, 2006 8:51 pm

Royalratch wrote:.

Start the engine and the temp guage creeps slowly up between halfway and red after about 5 mins then kind of hangs there.
The heater is on full blast but no hot air coming through -+

Temp guage still at the same point - no hot air to the interior.

Have never known this happen on a M40, but it's very common on M20s and can happen on M50s as well. It is important that when you fill the cooling system that the car is level or up at the front. Never facing downhill.
The cause is an air lock at the back of the head, and will cause no output from the heater, overheating, and a possible cracked head.
To release the airlock fill the header tank to the top, undo the clips where the heater hoses connect to the bulkhead, and pull the hoses just off the spigots so that the air, along with a little coolant, can escape.

Wed Dec 20, 2006 11:41 pm

Cheers Brian - you have possibly saved me so much grief.

Just out of interest, did I just change the water pump, belts, fan clutch and thermostat for no reason?!?

Wed Dec 20, 2006 11:52 pm

All good service items, so no harm done.
If the heater has worked before, this is not the basic problem. It's either airlocked or its not. I've never known any BMW airlock while in use.
Are you sure this car is actually overheating? or is it just the gauge says it is? Check the brass nut on the back od the cluster behind the temp gauge is tight before you try much more.

Thu Dec 21, 2006 12:05 am

It is overheating for sure as steam starts coming out the bonnet.

Since I changed everything and bled it, less steam comes out but still 'a bit'. Oh, and the temp doesn't climb as fast but still does creep.

There used to be hot air flow inside but now it's cold even if the engine is hot and it's set on full heat.

If I release the airlock as you describe and it still overheats, do you think it's a blocked/knackered radiator?

Thu Dec 21, 2006 4:39 pm

Okay, I wnet to the car today and started it up. After all night and half the day at just above freezing the engine went upto middle in minutes. That can't be right?!:mad:

Still no heat coming through to the interior, though both radiotor hoses and one of the bulkhead/matrix hoses are hot/warm.

There is steam coming out of the radiator.

My guess is, the rad is blocked, thus the whole system is just full of standing water just getting boiled.

The steam is a cracked rad trying to release pressure.

I'm going to change the rad and if it stil overheats then I truly am stumped.

Sun Dec 24, 2006 8:31 pm

Is it the rad then?

Sun Dec 24, 2006 8:46 pm

Royalratch wrote:. After all night and half the day at just above freezing the engine went upto middle in minutes.

Still no heat coming through to the interior, though both radiotor hoses and one of the bulkhead/matrix hoses are hot/warm..

Standard symptoms of an airlock in the head.
If the rad is cracked it needs changing anyway, as the system can't reach operating pressure, and is bound to lose water.