JMO
I run mostly water in our dagenham dustbins / alfas and they don't run hot.
It sounds more like pressurizing in the expansion tank / radiator.
Anti freeze makes the water less able to expel heat than straight water. The Anti freeze does stop corroding of aluminium bits, but only for the guaranteed time of the anti freeze (eg the inhibitors in it last 2 - 5 years before corrosion starts).
I've been through this with our Ford V8 for last few months. Ive used K-seal in the coolant system to stop the pressure of the cylinders from going into the water system - causing a rise in pressure.
I tested ours by borrowing mates pressure testing kit, you take off rad cap / expansion bottle cap and connect a pressure gauge where cap was. As you rev the engine you should see about 0.5 - 1 bar of pressure. If it goes above 1 bar then the system is pressurizing.
I don't want to be a panic merchant, just giving you the solution to our problem.
Cheers
Kevin