Two questions,

One, is there any reason why some coolant bottles are shaped in this way?

enter image description here

Two, if this coolant bottle was placed on its side such as in the image below for example would coolant still circulate with the return pipe submerged under water? In other words is there any reason why the coolant return is placed at the top of the bottle.

Don't panic I’m not getting any wild ideas of placing my expansion bottle on its side it is for a different project I am building to cool a series of GPU's (not related to cars) however the cooling system will be the same to that of a car as the pump will be a centrifugal impeller and the system will be pressurised.

enter image description here

Interested in all input to this subject thank you all for your time.

Please excuse the poor drawing in paint but i don't have time to draw something extravigant in CAD. one last thing the cap will be above coolant level to release excess pressure.


1 Answer 1


This particular bottle is knows as a degas bottle. The reason it has a strange shape is two fold. First, the bottle needs to fit somewhere and the shape helps that. Second and more important is that these degas bottles hold pressure. The shape reinforces the bottle so that it does not explode.

In cooling systems with degas bottles the coolant does not circulate through the bottle. The engine feed line connects to the lowest part of the engine and the "return" line connects to the highest point in the engine. This helps to fill the engine with coolant. As coolant is added to the bottle it flows to the lowest point in the engine. The air then escapes out the highest point in the engine.

Your plan will work with only one stipulation. These degas tanks tend to have separators inside. If the feed and return sides have a separator that is higher than the cap the system may overflow. A practical test may be in order. Here is another crappy picture as an example.

Another crappy picture

  • 2
    See i.sstatic.net/rZvTo.jpg Commented Feb 2, 2016 at 18:25
  • @LynnCrumbling That's awesome :-)
    – vini_i
    Commented Feb 2, 2016 at 21:32
  • that drawing is amazing. +1 Where did you learn that kind of precision? Commented Feb 4, 2016 at 0:42
  • .....fantastic drawing +1 from me too. :-)
    – Ppoggio
    Commented Feb 4, 2016 at 5:28
  • 1
    It's now in the national gallery for a limited showing. i.sstatic.net/rZvTo.jpg Commented Feb 11, 2016 at 18:02

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