1998 Chevy Blazer 4 wheel drive

It ended up being my transfer case was bad. Had to pay 1200 for a used one. Sorry I didnt explain myself well. I just posted another inquiry on here, would you possibly have an answer to that question.

Engine Cooling problem
1989 Chevy Blazer 6 cyl Four Wheel Drive Automatic 119000 miles

My engine temp gage said it was running about 225 and it usually runs about 190, and hot on my vehicle is in the 250's. Anyway, I checked my overflow tank and it was empty then checked my radiator and it also was low. Had to add a gallon on water and some coolant to the overflow and radiator. Does this mean that I have a leak or a water pump problem or is it common in vehicles to have to add fluid. I had my oil changed in March and I am assuming they also check my fluid levels on the coolant. And it wasn't a problem then. After adding the water and coolent I then took the vehicle out and drove about 25 miles and the temp stayed around 190. Are there gages that a mechanic can hook up to tell if there is a leak?
Can anyone let me know what you think.

Thanks
rhonda

I actually did put cardboard under the vehicle yesterday and ait had very little dripping on it but today when I went to my neigbors house about a half mile away and pulled into her driveway it was dripping pretty good but it stopped after it sat there for 5 or so minutes. I touched it with my hand but it felt mainly like water with not much of an odor to it if any. I then drove it home and it dripped again on the cardboard after parking it. I would say it was the size of a dinner plate. I had to add a little water earlier today to the overflow tank cause it had went down some from last night. The engine didnt overheat when I was driving it but I didnt drive it that much either. Yesterday I drove it about 70 miles and it didnt overheat after I added the water and coolant, But there is an obvious leak, so do you think I should still do the pressurized thing you talked about. The nearest mechanic is 90 miles from me and I hope that I can make it that far. I suppose I will have to keep stopping and adding fluid. I just hope that it is a leak and not something else that is major. I will let you know what I find out, do you have any more ideas as to the above stuff I mentioned.
Thanks,

Rhonda