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Discussion Starter · #1 ·
this thread will document my experience in the trial of a 1-bar radiator cap for the cooling system on my e46. i will document coolant temperatures, any noticable benefits, any noticable differences, etc.

the cooling system is presurized to 2-bar from the factory from BMW. a 1-bar cooling system will theoretically provide more reliable cooling system performance.

i will update this thread periodically. for those of you that have any questions, you can PM me or post in the thread. i work a lot and travel frequently for business, but i will update this thread as often as i can.

thank you,

bryce
 

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I thought our system ran at 1.5 bar but that the cap relieves pressure, if needed, when it builds above 2 bar...the limit of the cap.

It's a sealed system with a thermal expansion tank to buffer changes in pressure but the pressure increases when the car is running. I didn't take physics, but I'm confused a bit since I thought the system, at rest, would be at one atm. My initial thought in reading your post is that the car would relieve pressure when it's running.

How does a cap reduce the pressure at which the system runs without letting either air or coolant out?

Not arguing...just curious.
 

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Discussion Starter · #6 ·
from my limited understanding of how the e46 cooling system works, it's TWICE as pressurized as other mfg's cooling systems. it may be why the cooling systems fail and fail so "hard."

if you lower the internal pressure to 1 BAR instead of the 2 BAR OEM level, there won't be as much cooling system "headaches" or expansion tank explosions.


this is not intended to suppliment proper cooling system maintenance. SEE MANGO'S THREAD






this thread is simply an experiement by me and an un-named supplier. i will divulge the supplier when he gives me the go-ahead. at that point, this cap will be available to consumers.




my testing will include live monitoring of coolant temperatures, inspection of cooling system components, removal of cooling system components after sustained mileage, etc.



i hope this will benefit the e46 community as much as i believe it will. this could be a potential huge breakthrough in all the headaches associated with the e36 and e46 cooling systems. stay tuned for more details :)
 

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Reducing the pressure of the cooling system will reduce the boiling point of the coolant which in turn reduces the efficiency of the system.

Anyways, curious to see how this effects your operating temps under various conditions.
 

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So basically when the system is fully hot up to temp, when we loosen our caps that is why a lot of steam/hot air comes out. Wouldn't using this cap to lower the pressure force the water pump to work harder to move coolant around as it's not pressurized as it should be?
 

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So basically when the system is fully hot up to temp, when we loosen our caps that is why a lot of steam/hot air comes out. Wouldn't using this cap to lower the pressure force the water pump to work harder to move coolant around as it's not pressurized as it should be?
The water pump can only work at one speed since it is belt driven, unlike modern electrical pumps. It cannot compensate for the reduced cooling efficiency due to the reduced pressure.
 

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So basically when the system is fully hot up to temp, when we loosen our caps that is why a lot of steam/hot air comes out. Wouldn't using this cap to lower the pressure force the water pump to work harder to move coolant around as it's not pressurized as it should be?
No, the coolant system pressure has no bearing on how hard the water pump has to work when the system is sealed. The reason coolant spews out when you remove the radiator cap from a hot engine is because there is now a pressure differential between the pressurized fluid and the surrounding air pressure.

Cars use a pressurized system to raise the boiling point of the coolant. This in turn allows the car to run hotter (at a temperature regulated by the thermostat) for improved emissions, etc. Depending on how much margin is designed into the stock cap, one very likely outcome of this experiment is a coolant leak from the cap due to the thermostat allowing coolant temps to create more system pressure than the 1-bar cap will allow.
 

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Alrighty.


just for further discussion for the guys on the forum


http://www.carsdirect.com/car-repair/understanding-radiator-cap-pressure-ratings
Yup, that's what I thought. Lowering the pressure lowers the boiling point (as imolasix pointed out before me).

I'm not an engineer, but I can't see BMW making the pressure higher without good reason.

It's a neat idea and I'm in for results, but regardless of how it turns out it's not something I personally would do.
 

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If anyone can tell me the volume of the air in the expansion tank for the minimum and maximum fill levels (when cold), I can calculate the pressure range at which our cooling system operates. Very simple physics.

My guts are telling me 1 bar might be too low.
 

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Discussion Starter · #16 ·
If anyone can tell me the volume of the air in the expansion tank for the minimum and maximum fill levels (when cold), I can calculate the pressure range at which our cooling system operates. Very simple physics.

My guts are telling me 1 bar might be too low.
that may be true; i think the vendor is also exploring a 1.5 BAR cap to find a happy medium.
 

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A 1 bar cap will lower the boiling point of the coolant by about 43º F if i'm doing the math right. That's a big jump. You may throw things out of the range of expected inputs from the ECT sensor and other elements and cause issues.

I'm in for results. But 1 bar seems much too drastic.
 

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Has this supplier made caps for other cars aswell? If so do you know how those outcomes looked?
 

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This cap may work for casual driving, but what happens when you drive hard with it? You may get boiling coolant, which is totally ineffective at removing heat.
 
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