I'm guessing that you have an air pocket somewhere in the system.  Gases
expand more than liquids when heated.  Differences in the coefficient of
thermal expansion between propylene glycol and ethylene glycol probably
would not be noticeable.

Larry A.

Jfp w/3 WBXs wrote:
>
> Hi List,
>
> Recently, for my next WBX coolant service, I decided to try Sierra
> phosphate-free coolant instead of my usual Autobahn @ 11 bucks a gallon.
> My question deals with the expansion characteristics of Sierra coolant. The
> Sierra coolant seems to expand 2 or 3 times what the Autobahn does. When
> cold the Autobahn starts at the minimum line on the expansion tank and rises
> to below the maximum line at full hot. The Sierra also starts at the min
> line but rises to well above the max line(into the screw cap area) at hot
> idle with the aux fan on. The cooling system is functioning properly and has
> been bled correctly. It seems that the Sierra coolant just expands much more
> than the previous Autobahn. Anyone have experience with the cold-to-hot
> expansion behavior of phosphate-free coolants.
>
> Regards,        John
>
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