In terms of freeze protection propylene glycol would work just as well, in
fact better, than ethylene glycol if mixed in the proper proportion. The
"problem" with the pink propylene glycol is that it does not contain
anti-corrosion / anti-scaling additives that the green ethylene glycol does.
If you could find propylene glycol that was specifically formulated for use
in engines it would probably be OK. Most is sold for freeze protection in
RV and cottage water systems where its non-toxic property is needed.
As for changing antifreeze, the glycol does not degrade, it is the additives
which are used up over time. You can confirm this by having the freeze
point of your cooling system checked. If you constantly add water you will
eventually dilute the glycol too much and then it would need a change. The
additives would also be diluted this way. I imagine the long-life
antifreeze has more additive or a more stable type but if you frequently add
water you may negate this advantage.

"Jeff Morris" wrote in message
...
I'm in the middle of changing the antifreeze in my Yanmar 2GM20FC engines
and am
curious if I should change type.

I've been using Ethylene Glycol, following the advice of a Yanmar mechanic
who
said using Propylene Glycol would void my warranty. I've never been able
to
verify that, and I'm now long out of warranty so I'm wondering if its time
to
switch to the more environmentally friendly Propylene. I also think that
using
the easy to dispose propylene would encourage me to change more
frequently.

Secondly, if I do change, do I have to flush out all of the old, or is it
sufficient to just drain it?

TIA, Jeff