Russolini

Hello to all, and thank you in advance for any advice given. I have a 1996 Cherokee Sport, with 238,000 miles on it, I bought it 10 years ago with 98,000 on it. It has been the most reliable vehicle I've ever owned. The heater control valve blew up while driving(2nd time, so wasn't shocked), but was close to home and made it just as temp gauge was going almost to red. I replaced that this morning, careful to run the lines correctly. Topped off temporarily with distilled water as I had no coolant, (my girlfriends wretched little Subaru drank it all).Turned it on and proceeded to check for leaks(none). Picked up tools, then poked my head in drivers window and was shocked to see temp gauge maxed out. It had not really been running long enough to even warm up by normal standards. I guessing the thermostat failed simultaneously, possibly. I've used the search function but did not come across specific info on the subject. It is my only vehicle so I am dead in the water, and hoping some more experienced folks might have some thoughts on the problem. Thanx again for any knowledge passed along.