When I got the 6.0 in, I didn't have any coolant, so we just put straight tap water in. It's been like this for about 2.5 months. How bad is this? I know I need to flush it before it gets cold anyways.

 

Tap water has alot of minerals in it that will scale along with rust the coolant passages not to mention there is no "lubrication" for the water pump. If you used a few bottles of Water Wetter, you would be somewhat O.K. however still run the potential for scale and corroding the passages. Personally, I would dump the Tap water ASAP to avoid further corrosion. If you were only using Tap water temporarily (such as to drive to the auto parts store to pick up some glycol) you might be O.K.

 

+1
Flush it and add coolant.

 

I use tap water every summer. Never had any issues. I do have an aluminum block though.

 

even worse. The oxides that will form and corrode passages will cause you troubles later. Aluminum oxides are no better.

 

so my engine is screwed?

What problems will present in the future?

 

no not scewed, just drain and add the proper coolant. Tap water has minerals in it which will solidify and eventually corrode and clog the passages not to mention it has no corrosion preventive chemicals to rust also forms and solidifies. If you have no access to coolant add distilled water but never tap water.

 

your saying to fill with 100% coolant?

 

if it comes pre-mixed. otherwise follow the instructions on the label

 

A 50/50 mix of engine coolant and distilled water is a good rule of thumb...I usually get the pre-mixed stuff myself...