Read the label on your coolant - if it's premixed with water (it will say so,) you won't need to add any. If it's not, cut it about 1:1 with water that has either been distilled or reverse osmosis filtered (the R/O process takes less energy, and has roughly the same net effect.) Never use tap water in the cooling system or in the battery!
If you can find Water Wetter, get a bottle and you'll dump it in with your coolant. It's a "surfactant," and will reduce surface tension of the coolant (making for more intimate contact between the casting and the coolant, and between the radiator surface and the coolant; and therefore more effective heat transfer. I would not recommend this if I didn't use it myself, and I've been using it in every vehicle I've owned for a number of years...)
It is advised that you change your thermostat as well. Conventional thermostats are considered 'failed' after a single overheat episode (240* or higher,) and most people don't change their radiators on a whim.
Before you install the new thermostat, put it on your workbench. Get out your drill motor, chuck up a 1/8" or so drill bit, and drill two holes in the flange. They need to be 180* apart, and fairly close to the poppet valve (so inward on the flange, not toward the outside edge.) Install with one hole at 12:00 and the other at 6:00 - this makes your system able to purge air from behind the thermostat on its own.
Do this whether you have the "closed" (1990-earlier) or "open" (1991-up) system. If it's "closed," burping the air from it manually is a pain. If it's open, it just burps itself that much faster. Either way, if you get a compression leak into the water jacket, the compressed gas can escape from behind the thermostat and escape the system entirely.
Some other helpful little things you can do?
- Replace the hardware that holds the top of the mechanical fan shroud and the top of the electric fan assembly. The OEM stuff is some whacked ISO size (M3?) - you can usually find 1/4"-20 clip nuts and 1/4"-20 thumbscrews at your local harware store. You may have to enlarge the holes in the plastic slightly to pass the 1/4" screws, but you now won't need to find your 6m/m wrench, and can source new hardware easily (just get a few more 1/4"-20 thumbscrews. I use 1/4"-20x1".) Every time I have to remove the fan on an XJ that I'm servicing for the first time, I check to see if I can replace the hardware out of my hardware box. If I have the stuff, it goes in. Since I usually end up servicing that vehicle a good deal as it goes down the road (even if it's not mine...) I've just saved myself plenty of time in digging for that 6m/m socket I can never find, and making sure I don't lose those screws! I've not lost a clip nut yet, but I really don't want to lose one of the OEM ones. The 1/4"-20 ones I keep around anyhow.
- A bit of light silicone lubricant smeared inside the last 1/4" or so of the hoses will help them go on, help them, seal, and help them come off nexxt time. Don't use petroleum jelly - it isn't silicone lubricant, and is mildly antagonistic to the elastomer used to make "rubber" hoses. Silicone lubricant should be findable at your local hardware store - if you can't find it, use white lithium grease (it's based on a lithium soap, and not a petroleum product. Therefore, not antagonistic. I've used both.)
- If you can't get your old hoses off, you can slit them lengthwise with a new blade and push them sidewise (so the cut gets stretched,) that usually works neatly. Don't push so hard you score the nipple - it's either stamped brass (radiator) or aluminum (water pump/thermostat housing.) Why buy trouble when you get plenty for free?
- If it hasn't already been done for you, replace those OEM "spring wire" clamps with proper worm drive clamps. Tighten the clamp until the hose material just comes level with the drive grooves in the band, or the band just starts to dig into the hose. Check in 2-3 days for leakage, tighten PRN. If it's just a drip, usually 1/4 to 1/2-turn will do. No point in getting stupid - you want to seal the hose, not cut it.
- While you've got the radiator out, put a stream nozzle on your hose and blast out the aircon condenser fins from the engine side. Get the crud out - it makes the system more efficient.
That's all I can think of for the moment. You typically need 2-3 gallons of coolant for the radiator job (you can find the actual system capacity in the Tech section of my site.)
COOLANT DISPOSAL: There are usually a couple of methods available to you -
1) Take it to a radiator service shop. They'll usually take it for free - they've got a truck that comes around to filter the stuff, mix in a new additive package, and it gets put in bulk drums. Recycled on-site, it becomes their new supply.
2) Check with your local water company. In many cities, you're allowed to dump a certain amount of quite a few fluids you don't expect down the drain over the course of a month. For instance, SJWC sez a gallon of coolant a month is acceptable (although they don't advertise the fact.) They just want to limit it so you don't overload the purification system (although Autoland, last I checked, is still taking the stuff. They're up on De La Cruz, near the airport. I've been able to take in 5-10 gallons at a whack there, and they've taken it for free.) I only use the drain if I'm doing a "small" job - like replacing a thermostat (I only lose a few pints) or changing a RENIX coolant tank (pinch off the hoses, and you only lose about a quart in the tank proper.)
