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Discussion Starter #1
Anyone have a lower pressure release upgrade on their e60? Originally, the expansion tank cap is rated at 2.0 bar which is around 29 psi. There is a G.A.S solutions cap rated at 1.2 bar which, supposedly, helps prolong the life of cooling components, especially the plastic parts and weak points and also helps avoid larger or even catastrophic failures.

My question is; Is it safe to install a 1.2 bar cap on the system that BMW "designed" to run at 2.0 bar?
 

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I don't think it's a good idea .. Because the lower the pressure , the lower the boiling point .. if your concerned about failures , a cracked expanding tank for instance . It's better to just run the coolant at the minimum level . Thus creating more space in the ET for expanding coolant ..
 

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Under the lift arms
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been hearing this for like 20 years..

the problem is not the exploding cooling system.. The problem is that your cooling system needs replacement

and i strongly suggest yielding to my advice..

replace it all together at the same time

every plastic part is brittle and ready to crumble and you will see when you start taking it apart,

Replace at least the major components together (all the hoes, the aux pump the tank)

it will nickle and dime you for years to come if you do not..

it was the same way with the m62tu in the 540, same story different chassis
 

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Under the lift arms
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and if your really gun hoe about it,

after you replace your cooling system, you can switch to evens water-less coolant... (zero pressure system)

BUT doing so now.. on a old cooling system is a really good way to throw away 100$ worth of coolant
 

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If you have gone to the low temperature thermostat with your v8, then you can use the 1.2 bar cap with now problem. The 2 bars of pressure is.not needed as the engine is running something like 15-18*C cooler at operating temperature.
 

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02/2012 X5 35d M57Y CPO 99K miles NOKIAN WR G3 12K miles
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The efficiency of an internal combustion engine is fixed (to some decimal places) by its design. Its inefficiency is in heat rate that must be removed by the cooling system at the design operating temperature.
 

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Discussion Starter #7
The boiling point of water at 2.0 bar is around 120 degrees C. At 1.2 it's around 105 degrees C. A 50/50 mixture of HOAT (blue) coolant boils at 108 degrees C at 1.2 bar. The pressure build up never reaches 2.0 bar unless there is something wrong, however, the pressure also never reaches 1.2 bar, unless you are at higher altitude. Wouldn't that mean that there is some or more than some science behind the design of the 1.2 bar coolant cap?
 

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The point Doug is making is that a heat engine's efficiency is directly related to the operating temperature. So, the designers are paying particular attention to the operating temperature of the engine, part of which is moving the boiling point up a bit using a pressurized system.

Now, the car's computer has no way of knowing you put in a lower pressure cap and will not compensate properly for it's use. The cap is normally closed and that means the closed cooling system is operating at something less than 2 bar. By putting in a lower pressure cap, you are just going to lose coolant sooner when the temperature rises above 1.2 bar due to temperature fluctuations.
 
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