Your E-mail asked about flushing at/where the thermostat is at-yes, but you will need to remove it first. If you think the thermostat is froze open (does it take a long time to warm up?). If you think it is froze then it is easy to replace. Install the new thermostat with the spring part going into the cylinder head, do NOT over tighten the bolts(156 inch pounds)- you can need to use a inch pound torgue wrench (unless you have been wrenching a long time and know the "feel" . Use a new gasket, scrape the old one off completely off block and housing. install the new thermostat with the small hole at the 12-o-clock position. use black silicon sealer on the cyl head and housing -so it will definitely seal the gasket. Now that it is flushed out-you can use what ever antifreeze you want. If you buy in undiluted-mix use only with DISTILLED water ( $.89 at Wal-Mart)--- (NOT water from your facet), unless you want to be doing this again. This information is for a 4.0L 6 cyl. 10.5 qts of MIXED coolant and DISTILLED water at a 50/50 ratio . Or you can just buy the pre-mixed stuff, its just more expensive that way. FWIW I use the prestone green stuff and change it with the same every 3 yrs. don't mix different brands. If you want to use another-OK, keep using the same stuff. I'm out of breath!