Where did you see this 20 deg C spec?

 

Edjack it can be found in the owners manual

 

You are correct, sir! Shame on me for not looking!

 

The correct procedure demands that the engine is cool.

The level should be just below the max mark at around 20C. However, this does not mean that the temperature has to be around 20C when you check the level.

 

Well to get accurate level it required to be at the specified temperature. If it was plain water, going from 20C to 0C means about ~0,2L decrease in volume (That is with 12L coolant capacity, which is what the V8 has, I'm not sure about the I6). I don't have the thermal expansion coefficient for coolant and I'm too lazy to google it, but it should be in the same neighborhood. The bottom line is, if your a bit low on coolant when checking it at 30F don't top it up, because you'll have too much coolant.

 

You are only off by an order of magnitude. The volume will decrease by about 0,02L (less than a shot glass).

 

I always run mine a bit low, the stick 3/4" below the top.
Less pressure build up in the system.
Been doing this for 3-4 years with no issues, just a lower pressure reading in the gauge I installed in the radiator.

 

That is good approximation. I will do the same. I could not find thermal coefficient of expansion of coolant.

 

Pressure gauge installed in the radiator? DIY here or details in a old thread available? Peaks my interest.

 

pressure gauge in cooling system



I'm not sure I see the value in a pressure gauge on the cooling system unless one want's to monitor/detect a faulty radiator cap, aka pressure relief valve. A flowmeter might make more sense.....detect that coolant fluid flow and monitor the water pump's performance; but this is a more expensive and bit more complex an install than a pressure gauge

 

how to determine correct coolant level when that "reddish" stick is broken.mine is in the middle of the black coolant tank.

 

Coolant level at middle of tank is where it should be.

http://www.bimmerfest.com/forums/showthread.php?t=681851

 

JimLev posted pressure gauge readings in this thread...
- How to modify the cooling system expansion tank 2 bar cap to 1.2 bar to vent at a lower pressure (1)
See also:
- What is the proper coolant level bobber stick height (1)
And ...
- How the expansion tank works (1)