I've had a problem over the years with the coolant becoming rusty and rust depositing in the coolant overflow reservoir. I use distilled water and Barrs Antirust/Waterpump Lubricant or a similar antirust from NAPA. I don't use antifreeze since I live in Florida. The antirust manufacturers say that this is OK.

Is there maybe a special antifreeze that might be a better antirust agent?

Also I notice that when opened cold, the radiator is not full to the very top, even with a new radiator cap and overflow reservoir at the full mark. I'm wondering if there may be a tiny head gasket leak allowing a small amount of exhaust gas into the coolant with resultant rusting from it's chemical action.

Any info would be appreciated.

 

I work at a Hyundai dealer in Florida and we always use the Hyundai coolant part number 00232-19010, I would not suggest anything else.

 

= mistake #1

Deionized/distilled water promotes rusting

= mistake #2

Antifreeze is way more than just that. It cleans, lubricates, prevents cavitation & rust if used in the right concentration. Prefabricated water/antifreeze mixtures (as is the Hyundai coolant mentioned above) are the best/easiest, yet a little more expensive solution over mixing the components yourself.

 

I would agree. Straight distilled water is not good. Buying the 50/50 pre-mix or using equal parts 100% antifreeze and distilled water is the best option. Like was said above, quality antifreeze isn't just to prevent the coolant from freezing.