98 cadillac leaking coolant. live in arizona, hardly ever gets below freezing. internal repair too expensive. adding 50/50 dex cool often but also too expensive. my question: what if i simply add water without coolant mixture?
No. Coolant not only keeps the fluid from freezing, but it also helps keep it from boiling and it improves heat transfer. Using water is likely to cause overheating and further damage.
I suggest that the repair may be cheaper than ignoring it.
Also, water has no corrosion inhibitors. The aluminum in the engine will get eaten alive. And water has no water pump lubrication. You will destroy this car quickly if you run straight water in it. The repair will be the best option.
If it is an intake gasket leak, common with Death-cool, the repair may not be as bad as you think. Shop around some independent shops for a better answer. If it is a head gasket, it will only get worse, and either fix it or pitch it is the best answer I can give.