Ditto what Rich P said. The Kriket II is worth it's weight in gold. I also get my fan clutch at carquest.
I take it you are changing the items on the 91 XJ not the 2001 XJ.
I am the type who changes radiator hoses, heater hoses, fan belts, and radiator cap every 4 years. I recommend you do the same. I use a goodyear belt, Dealer hoses and the cap that comes with me new pressure reservoir. your 91 is the "open" cooling system so no pressure bottle for you! I'd also install a new thermostat, I get that at the dealer also.
While I have the belt off I'd change the idle pulleies as a preventive measure, you know the one by the AC compressor. For my 88 XJ the "new" belt tension is 180-200 lbs. Put the kriket II on the section of belt between the idle pulley and the power steering pump, that the right location to take the measurement. For a used belt it is 140-160 lbs, used is a belt with more than 15 minutes of use.
Just do every job you can think of while you have the radiator out. Also use distilled water when refilling. It avoids problem and at 80 cents a gallon what 3-5 bucks to flush an fill with distilled. I also use the craigh method of refilling - point the XJ down hill if possible, pull the temp sensor out of the head, fill with coolant/water until it comes of out of the temp sensor hole, replace sensor.
I also found with just water in the block after flushing I'll pour in 6 quarts of full strength coolant then pour in water to bring it to full. It is published the cooling system capacity is 12 quarts. If you do it this way then you will have a 50/50 mix.
