New guy has aux fan woes

[Jay 535i]

theres no clearence to do it inplace and theres no way to access the hole without removing the hose, i've tried to clear them with a pick or wire though the cap and it just doesn't get it

Alright. Thanks so much for your help and patience. I'll try this later and let you know how it goes.

Remember earlier I explained that when the thermostat opens, coolant comes spewing out the filler if the cap is off. If all that coolant isn't coming from the hose you'd have me drill out, where's it coming from? And how?

[Kalevera]

Alright. Thanks so much for your help and patience. I'll try this later and let you know how it goes.

Remember earlier I explained that when the thermostat opens, coolant comes spewing out the filler if the cap is off. If all that coolant isn't coming from the hose you'd have me drill out, where's it coming from? And how?

What's probably happening is the coolant is boiling in the water jacket and the pressure pushes it back up through the (larger) expansion tank hose, giving the volcano effect.

By the way, how do you know that the thermostat is opening?

best, whit

[Jay 535i]

What's probably happening is the coolant is boiling in the water jacket and the pressure pushes it back up through the (larger) expansion tank hose, giving the volcano effect.

By the way, how do you know that the thermostat is opening?

I assume the termostat is opening because the volacano, the heating of the rad top hose, and the needle reaching the half-way mark all happen at exactly the same time.

If the cause of the volcano, as you put it, is not somehow related to the opening of the thermostat, then this would seem like an awfully big coincidence. No?

On the other hand, if the volcano is somehow related to the opening of the thermostat, how would that work, exactly?

[Kalevera]

Jay

There are probably a couple of things going on with the car's cooling system.

Cooling systems work under pressure. The combination of antifreeze and water, when pressurized, have a higher boiling point than when not. Leaving the cap off of the expansion tank while a few gallons of coolant in the engine block and cylinder head start to cook means that the components of the mixture start to boil, especially if there's something wrong with flow, or the coolant's bad. As we know, boiling most liquids turns them into gasses. The gas has to go somewhere, so it starts to push coolant out of the expansion tank. This all makes sense if one of two things are happening: 1) the coolant isn't circulating, either through the radiator or through the block, or 2) the head gasket/cylinder head/block are somehow compromised (read: cracked).

Now, the thermostat in the M30 does one very crucial thing, and performs another task of lesser import. Primarily, it acts as the valve between the cylinder head and the radiator. When closed, no coolant from the radiator gets moved back into the block. The secondary task is one of manipulating a valve within the thermostat housing that directs coolant flow. While the thermostat's busy doing its thing, the water pump is happily uh....pumping...away: it picks up coolant from the water jacket and sends it right back to the thermostat housing. With a closed thermostat and (hopefully) a working expansion tank return line ('pisser"), some of that hot coolant gets pushed into the radiator via the upper radiator hose and back up to the expansion tank via the pisser. The rest gets circulated through the engine until the thermostat opens.

Because of the heat transfer through the liquid, the upper coolant hose will be as hot as the coolant in the engine is; it won't tell us anything about whether the thermostat is doing it's job. What will is the status of the lower radiator hose, which goes from being "cold" to "warm" as the thermostat opens, allowing the hot coolant to flow through the radiator, lose some of the heat, and flow back to the engine.

I've said it a few times before and I'll say it again: I don't think the thermostat's opening correctly, if at all.

Another thought: while probably not the only cause for its non-working state, having an inoperative tstat explains why the aux fan isn't powering on in overheating situations. The temp switch lives at the cold side of the radiator; without coolant flow, it doesn't know how hot the other side of the radiator is getting, and therefore won't turn on. It may be attributed to other issues (ballast resistor), but I'd suspect the coolant flow problem first.

Finally, here's a thread that detailed my experiences with this problem: http://www.bimmer.info/forum/showthread.php?t=9585

It's a lot of reading, but might help you out.

Good luck!

best, whit

[Jay 535i]

Jay

There are probably a couple of things going on with the car's cooling system...

Thanks a lot. That's really clear now.

I will try replacing the thermostat and see what happens.

What thermostat do I buy?

Do you have any tips/cautions about proper installation of the tstat that I won't get from the Bentley manual? I've taken note about what you've said regarding the O-ring.

BTW, when I said that the hot top rad hose indicated a working thermostat, I got that from the Bentley manual. Didn't make it up

[dacoyote]

Bentley isn't perfect...

better then Hayes but not perfect....

-Charles

[Jay 535i]

Well, I did as you guys said, and the overheating has stopped.

I jimmied open the crimped clamp on the hose, removed the overflow tank, and pulled the two apart. To be thorough I undid the other end of the hose at the rad, too. I cleaned everything out.

If there was anything lodged in there, I didn't see it, but there you go. Problem solved.

A million thanks to everyone who helped out.

'Til next time...