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24K views 104 replies 39 participants last post by  klax 
#1 ·
OK. new to BMW. Fine car. But it seems like cooling system issues are common.

I understand that plastic fails with age, and that is a likely cause of system failures.

But I can't help wondering if the design is also part of the problem.

Many (most???) cars use an overflow tank and a pressure relieve valve in the radiator cap. If the pressure gets too high, the excess fluid is directed to the overflow tank. When things cool down fluid is sucked back in from the tank.

It seems BMW uses a closed system with an "expansion" tank. I guess the idea is that the radiator will always stay filled with liquid - as it expands it compresses air in the expansion tank to make room. If somebody overfills the system there is not enough room, and something explodes. Exploding seems common here. I wonder if perhaps this is due to not leaving enough air in the expansion tank. Or maybe it is user error - if you fill above max you will likely have an explosion since the expanding fluid has no place to go.

So, anybody know why they designed it this way? Is there any over pressure release valve at all in the BMW system? If not, seems like a recipe for disaster.
 
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#5 ·
e46's expansion tank is also its overflow tank. There is an overflow valve built into the expansion tank. As long as you don't fill it up above the overflow tube, you should be fine. This level is higher than the maximum fill level specified on your ET. Just don't fill it up above that level.

The overall design of e46's cooling system is not the reason why those parts fail quicker than, say, Japanese cars. BMW engines run hotter than most other cars' engines (good for efficiency), which means your cooling parts have to work harder than most other cars'. Solution? Just be on top of your maintenance, and replace them before they break.
 
#7 ·
I assume the M3s dont have the big failures partly due to a better designed cooling system but mostly due to the owners taking better care of their cars due to the larger values of their cars and most are more likely to be enthusiasts.

This comes from a non m3 owner.
 
#8 ·
I think that cars used to have an overflow tank, but I suspect that most are now have pressurized expansion tanks. It reduces parts count, and so reduces cost. The cap on the expansion tank vents any excess pressure, and if overfilled will vent the excess coolant as well.

Both of my other cars (Lincolns) also have pressurized expansion tanks and no overflow. Unfortunately, they also have a similar failure rate for the tanks and other plastic cooling system parts. On the good side, they have failsafe cooling, so no engine damage if the cooling system fails.

I've had other cars with pressurized reservoirs that had seemly bullet proof cooling systems. Maybe they used better plastic?
 
#18 · (Edited)
My theory has been that the reason why they use plastic is because 1) its cheaper to make I bet and 2) they need parts on these cars to only survive the warrenty period. what happens when the warrenty is over for the second or third owner? they pay right out of pocket. i believe thats why some things on these cars have been designed the way they are
 
#19 ·
I have no gripes with our cooling system, who am i to question it's design anyways.

However I have been driving BMWs for 8 years, and the initial shock of maintaining them has long long passed.

Bottom line, the design of this system is rock solid when well maintained, all that is required of you is to maintain it, and do it correctly.
 
#29 ·
So first, I read that the M3 doesn't have the same set up as non-Ms but I'm not so sure about that. I know there's a hose crossing over to the ET that we don't have, but I think that's just the way it makes the same connection we have to the ET from the upper hose. Just a hose instead of it being incorporated into upper hose fitting.

My car's second ET lasted 9 years. 9 years...and probably a good 200K miles. The first ET was replaced after 2 years.

I do think ET's fail because of overfilling...and made a thread about that...forget the title...maybe 'plastic or human error'?

My window regulator on driver's door was original up until a year or two ago. They're not crappy parts...they're just susceptible to owners who are misinformed, ignorant, dirty, or busy! I think regulators probably fail more because of owners opening windows when they're frozen...or maybe had been closed a long time in the heat and got stuck. Combine that with lack of a preventive and sensual coating of gummi pflege...what do you expect?

Most cars don't have an ET like we do. Jaguar does I know...not sure who else, but not everyone at all.

Our expansion tank is a thermal expansion tank...like in your home's thermal expansion tank. In conventional systems, the extra fluid leaves to overflow tank and returns...as explained. In ours, the air in ET (maybe 2 cups of it) is what buffers, cushions, the system. Air compresses much easier than water, you know, but when coolant heats, it expands and needs a place to go. Don't give it the air, it will take out an ET.

Also, have to say it doesn't bother me having a system that will blow apart before the engine does. If it was as rock solid as it seems some of you want, you'd then be moving extra pressure to where? The head gasket. No thanks, I'd prefer just replacing ET please.

Don't go hating on BMW guys. Continue on like this and your penance will be severe!
 
#31 ·
My window regulator on driver's door was original up until a year or two ago. They're not crappy parts...they're just susceptible to owners who are misinformed, ignorant, dirty, or busy! I think regulators probably fail more because of owners opening windows when they're frozen...or maybe had been closed a long time in the heat and got stuck. Combine that with lack of a preventive and sensual coating of gummi pflege...what do you expect?
Pretty much every BMW since the mid 90s or so has been plagued with window regulator issues. To suggest that parts fail because they needed lubrication (jokingly or otherwise) pretty much confirms they are poorly-designed and/or poorly-made.
...the air in ET (maybe 2 cups of it) is what buffers, cushions, the system. Air compresses much easier than water, you know, but when coolant heats, it expands and needs a place to go. Don't give it the air, it will take out an ET.
...no. PV=nRT so temperature and pressure are directly proportional. And pressure is pressure, with or without the air in the system.
 
#43 · (Edited)
Pretty much every BMW since the mid 90s or so has been plagued with window regulator issues. To suggest that parts fail because they needed lubrication (jokingly or otherwise) pretty much confirms they are poorly-designed and/or poorly-made.

...no. PV=nRT so temperature and pressure are directly proportional. And pressure is pressure, with or without the air in the system.
Your last statement is true but misleading. If the system has no air (meaning it is a solid system, all water), then a small increase in temperature can create huge pressures. Water does change density with temperature a little bit. However water hardly changes density with pressure. If you heat a solid system, you will blow it up very quickly. For example, given constant volume, water at 1 atm and 25C heated to 40C will then be at 110 atm pressure. That is insane.:yikes: i.e. overfilling the cooling system WILL blow up your ET.
 
#33 · (Edited)
If you look at window regulators from German cars made in the 70s and early 80s, they're pretty indestructable. They'll last for decades before a motor or switch will usually fail first. As Icoleman said, the bean-counters have won and we're stuck with the current, cheaper design.

I've owned several older German cars (I keep them a long time) and have yet to experince a regulator failure until my E46 (two failures).
 
#37 ·
The biggest problem with the ET is that it is very complex, with internal components that mean it has to be hand assembled and bonded together. The failures are mostly due to failures in that bonding process, and the fact that early ET's did not have enough internal bracing in critical areas. I am sure that if they could do it over, they would. It is just too complex, and it relied too much on the integrity of that bonding agent. Even if they had made the pieces with an interlocking joint that was then bonded, it would have been better. Instead, they are bonding two flat surfaces, which is never ideal. I have a feeling that some vendor overstated the ability of their glue to hold these things together through thousands of heating and cooling cycles.
I have not looked at the tanks on the newer models, but I would hope that they have applied some lessons learned from the e46.
 
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