Is this serious? Or did I do something stupid?

[littleredrooster]

steve_bmw said:

I think you've missed the point of my first post, the only reason water will blow out of the expansion tank is if its super heated with combustion gasses from a failed head gasket, over filled or a massive airlock.

Utter drivel.

If the running water temperature inside the block is 110 degC, releasing the pressure by taking the cap off will mean that the water will spontaneously boil and come out to atmosphere.

Why do you think cooling systems are pressurised?

[redstu]

My Passat used to lose water and I couldn't spot where it was going.

It was only when the car was in for a cambelt change that VW noticed a tiny leak in the radiator. Changed the rad and no more leaks. I cant remember the rate of loss but it was less than you have, possibly a litre every 2000 miles.

[Ozzie Osmond]

steve_bmw said:

I think you've missed the point of my first post, the only reason water will blow out of the expansion tank is if its super heated with combustion gasses from a failed head gasket, over filled or a massive airlock.

This isn't right. See littleredrooster's post (above) and also my post on the previous page.

Water in a hot cooling system is above its normal boiling point of 100 Celsius but does not actually boil because the cooling system is pressurised. As soon as pressure is released ALL of the water boils, including the water inside the engine, and scalding risk ensues.

In the old days radiator caps used to release with a quarter turn, leading to a serious risk of scalding. These days the cap tends to be on a long thread so that pressure releases more slowly. However, care is still advised.

[steve_bmw]

littleredrooster said:

Utter drivel.

If the running water temperature inside the block is 110 degC, releasing the pressure by taking the cap off will mean that the water will spontaneously boil and come out to atmosphere.

Why do you think cooling systems are pressurised?

So tell me why after an hour of driving I can remove my cap and no water boils out of my expansion tank? Is there something wrong with my car?

[littleredrooster]

steve_bmw said:

So tell me why after an hour of driving I can remove my cap and no water boils out of my expansion tank? Is there something wrong with my car?

Ergo the water inside your block is less than 100 degC. Most/many cars aren't, and removing the pressure cap is a highly dangerous thing to do.

[steve_bmw]

littleredrooster said:

steve_bmw said:

So tell me why after an hour of driving I can remove my cap and no water boils out of my expansion tank? Is there something wrong with my car?

Ergo the water inside your block is less than 100 degC. Most/many cars aren't, and removing the pressure cap is a highly dangerous thing to do.

Ok I'm with you, so my cooling system is working fine then, under what circumstances would cause the water to get so hot it boils out of the tank when I remove the cap?

[bearman68]

TurboBlue said:

When the HG went on my E39 the bill was £1,300 (incl. VAT).

I did a 325 HG on a customers car, with a new rad, water pump, thermostat for £650, and made about £20 for 40 odd hours work Duhhhhhh, not doing that again. Going to charge £1300 next time.

[Herman Toothrot]

This has been said many times already it'll always boil over if you open it when at running temp EXCEPT if its an overflow type setup like I said old mx5's have. I.e. the overflow is on the other side of the pressure cap. I don't know if your BMW has that or not maybe it does you need someone who understands and is familiar with them really. No cars I've owned other than the mx5 had that setup.

Most cars, the expansion tank is under pressure and doubles as a swirl pot and its very dangerous to open the cap unless the cars had plenty of time too cool down.

Edited by Herman Toothrot on Wednesday 31st July 23:15

[Ozzie Osmond]

steve_bmw said:

So tell me why after an hour of driving I can remove my cap and no water boils out of my expansion tank? Is there something wrong with my car?

It depends where you've been driving. After an hour round town I'd expect the cooling system to be right up to temp and fully pressurised, especially in summer. If you were cruising on a motorway the water in the radiator may stay quite cool, especially in winter.

The cooling system contains a thermostat. Contrary to popular belief the thermostat doesn't adjust the temperature of the coolant, it simply opens when the coolant in the engine starts to get too hot - and closes again once a new batch of cold coolant is detected. Obviously if all the coolant is up to full temperature the thermostst stays open all the time.

One of the typical signs of thermostat failure is seeing the temperature gauge fall below "normal" on the motorway. In other words, the coolant in the engine is being let out before it's got to normal temperature. (Note: thermostats are generally designed to fail in the "open" position to prevent overheating.)

[Benj1984]

I'm a technician with 12 years experience, depending on the type of cooling system, you can slowly undo the cap when the coolant is hot.

In a cooling system with an expansion tank, not a direct rad cap found on jap cars, the coolant in the bottle won't be as hot as the coolant circulating around the engine will be. Also, a cooling system has coolant in it, the boiling point of coolant is higher than water. Most modern systems will not boil over. You will get a release of pressure and the caps off. No drama. I have done this hundreds of times on all makes models. Only today I replaced an engine, blead the coolant, road tested it for 8 miles, back in the workshop idled it to get it fully hot with high speed fan cutting in i removed the cap with the engine running. Small release of pressure. I'm still alive.

And please don't patronise me with the preventative maintenance about the cooling system on BMW's. you do not need to replace everything on the cooling system in one go. Preventative maintence is when you replace parts that are worn, or visably close to failure, not just everything on the car because somebody on a forum told you so.

[steve_bmw]

listen to this man he knows what he is on about.
It's hard work sometimes. Lol

[steve_bmw]

littleredrooster said:

Utter drivel.

If the running water temperature inside the block is 110 degC, releasing the pressure by taking the cap off will mean that the water will spontaneously boil and come out to atmosphere.

Why do you think cooling systems are pressurised?

Coolant has a boiling point of 113 degrees, in the BMW system there is 15 psi of pressure, this raises the boiling point of the coolant to 138 degrees, my water going round the engine is at 110 and it always has been as i have a tell tale sticker on the hose, so why would it boil?

[Sump]

Actually, just chuck some uv dye in the system. Then look where it has leaked.

[Mr2Mike]

Benj1984 said:

I'm a technician with 12 years experience, depending on the type of cooling system, you can slowly undo the cap when the coolant is hot.

In a cooling system with an expansion tank, not a direct rad cap found on jap cars, the coolant in the bottle won't be as hot as the coolant circulating around the engine will be. Also, a cooling system has coolant in it, the boiling point of coolant is higher than water. Most modern systems will not boil over. You will get a release of pressure and the caps off. No drama. I have done this hundreds of times on all makes models. Only today I replaced an engine, blead the coolant, road tested it for 8 miles, back in the workshop idled it to get it fully hot with high speed fan cutting in i removed the cap with the engine running. Small release of pressure. I'm still alive.

There have been enough people with serious burns from boiling coolant (including myself many years ago) that shows your assertions are absolutely incorrect. However, as I said, if it's an expansion tank rather than a header tank or radiator then it should be quite safe.

Benj1984 said:

And please don't patronise me with the preventative maintenance about the cooling system on BMW's. you do not need to replace everything on the cooling system in one go. Preventative maintence is when you replace parts that are worn, or visably close to failure, not just everything on the car because somebody on a forum told you so.

No one has said change it all at once, but the point with cooling systems is that you very often can't tell when components are on the verge of failure. Plenty of coolant hoses are well hidden, and you can see only a small part of the radiator core without a lot of dismantling. Odd how many BMW specialists sell a complete kit of cooling system components isn't it?

Please don't consider yourself patronised, just better informed now.

Edited by Mr2Mike on Thursday 1st August 08:03

[Mr2Mike]

steve_bmw said:

Coolant has a boiling point of 113 degrees, in the BMW system there is 15 psi of pressure, this raises the boiling point of the coolant to 138 degrees, my water going round the engine is at 110 and it always has been as i have a tell tale sticker on the hose, so why would it boil?

Because that's only the case with fresh coolant at the recommended mix. As it ages, or if it gets replaced with a weak mix, or if someone tops it up with water the extended boiling point is lowered.

[Leemcd]

For a car with 147k is it worth a huge repair bill?? i had an issue with a car losing water. The cure came in the form of K-Seal! (granted the car was an old shed) definitely worth a try if the car is heading for the scrap yard anyway..

[Ozzie Osmond]

Benj1984 said:

And please don't patronise me with the preventative maintenance about the cooling system on BMW's. you do not need to replace everything on the cooling system in one go. Preventative maintence is when you replace parts that are worn, or visably close to failure, not just everything on the car because somebody on a forum told you so.

All very well for you sitting in your garage waiting for cars to be presented for repair. For owners, these are the questions,

• how much does a thermostat cost?
• how much does a water pump cost?
• how much does coolant cost?
• how does the labour charge for doing all these jobs on separate occasions compare with doing them together?
• how inconvenient are multiple trips to the dealer?
• how inconvenient/expensive is breakdown recovery?
• what's the risk/cost of engine damage through coolant loss?

[Ozzie Osmond]

steve_bmw said:

my water going round the engine is at 110 and it always has been as I have a tell tale sticker on the hose, so why would it boil?

Enjoy the link,

http://www.youtube.com/watch?v=zuwuZhoKKak

Coolant in the block is often hottest AFTER the engine has been switched off because the water pump has stopped. Typically just the time when the driver opens the bonnet to check the coolant level.

[steve_bmw]

Ozzie Osmond said:

Enjoy the link,

http://www.youtube.com/watch?v=zuwuZhoKKak

Coolant in the block is often hottest AFTER the engine has been switched off because the water pump has stopped. Typically just the time when the driver opens the bonnet to check the coolant level.

That's a radiator cap, not the expansion cap, different system to a BMW.

[Benj1984]

Can't believe this is still being argued. As me and steve_bmw have said numerous times. It does depend on what cooling system you have. And the one on the BWM is fine to open. You obviously open the cap carefully and gradually, so that if there is a problem you can screw it back on. Same with a rad cap. I've opened them when they have been too hot, and water has boiled out, but I've opened them gradually, applying pressure so that when it boiled out it was for a split second and I had time to screw the cap back on. This stuff is bread and butter, and I can't believe I'm being sucked into an argument about it.