Need to replace viscous clutch, possibly radiator and heater core. Some questions...
 

Okay so I can breathe a sigh of relief, my block test and pressure test came back negative. No exhaust gas in the cooling system, no leaking anywhere.

Next step? Viscous clutch (which I know is bad) and possibly radiator. The previous owner used dex-cool and didn't suck all the air out of the system, so who knows what kind of sediment was formed and clogged the parts.

The heater, even under overheat conditions, does very little to heat the cabin, so I'm thinking it's clogged. The radiator is probably just as bad.

What year clutch will fit on my 1998 discovery? Is there something better than stock (i.e. a DII clutch/fan combo, etc?) that will have even more cooling capacity? Same goes for the radiator.

As for the heater core, how do I get to it and how difficult is it to replace? Should I replace the hoses and whatnot too?

Thanks and hopefully I'll have a reliable LR again very soon!

Here is what I would do, drain the system and remove the thermostat.
Stick your garden hose into the t-stat opening and back flush the block with water, once it comes out clear then do the same thing with the radiator.
Then remove your heater hoses and do the same thing to the heater core.
Also flush your coolant reservoir.
Now put it all back together and fill it with water, bleed the cooling system of any air and then drive it for a day or two, use the heater once and awhile too.
Then drain and see how dirty it is, if it does not come out clean or next to clean do this again.
Do not drive it for more than a 100 miles or so with just water in it as one of the things that engine coolant does is lubricate the water pump bearings.
Once that is done replace all of your coolant hoses, heater lines too.
Atlanticbritish.com sells hose hits, replace all of your clamps and your t-stat and gasket too.
After that is all done then we will see if you need a new radiator and heater core.
As for the fan clutch, I have been told that www.motorcarsltd.com has the best prices on them.
That is what I would do before buying a $600 radiator.
I have never replaced a heater core on a Disco but I have on my wifes Volvo with duel zone HVAC and it was a 2 hour job.

http://www.discoweb.org/forums/showp...9&postcount=15
If Spike's hints don't work, take your radiator to a good radiator shop and have it rodded. They can probably tell if it will work with just that. One risk is that the sediment is clogging the hole that have rotted in it, and cleaning it out inside will let it leak.
If it's too worn for being rodded, if the tanks are good you can have it recored.

Replacing the heater core is a bitch. You have to completely remove the dash. Some people claim they could do it without removing the dash, but I couldn't see how when doing mine. Replace the two heater pipes that pass through the firewall too. You don't want to have to do the job twice. I assembled the pipes and heater core before installing and pressure tested it with a garden hose. I didn't want to have to pull it all apart again if it leaked.
I'd allow a long day to do the job start to finish.

People have reported you do not have to remove the whole dash to replace the heater core. Between taking out the glove box and pulling down the liner from under the dash you supposedly have enough room to get it out and in.

If you have air in your system, your heater core will not do a good job even under a overheated condition. Air loves to get trapped in the heater core. I dealt with this when I did my heads. It took me a few bleeds and toying with the heater core hoses to get all the air out. Before you think you need to replace your heater core, bleed, bleed and bleed to make sure you have all the air out. I have personally not seen anyone on this forum replace their heater core because it's not heating the cabin. They replace it because its leaking. How many miles? The heater core is something you do not want to mess with if you don't have too.

I actually replaced mine because I was replacing the two pipes going to it (one rotted off), and there was no way I wanted to do that job twice, if it started leaking later.
I did drive it for over a year with the heater taken out of the coolant loop.

Is there a more efficient/more powerful fan/clutch combo? I swear I saw a DI with a DII fan and boy did that thing move air!

I dont know if a DII fan will fit a DI, but with a properly working DI cooling system with its 3 core radiator (DII is a 2 core) the truck will not overheat no matter what you do.
If you want to move more air then use a HD fan clutch, it will turn the fan on at a lower engine temp.
But keep in mind the more you use the clutch fan the less your MPG will be.

I had to replace the water pump on my '97 and already had a water pump with the fan attached from a '98 Range Rover. ( I believe this is the same as DII's) Water pump fit and fan did work but I had to permanently take off the removable fan shroud because the fan was a larger diameter. This is the fan where the blades are connected with an outer ring unlike the DI's open fan blades.

Let me add that although the water pump fit the engine, I'm not sure if it actually is the same one for a DI. Since the new fan was already attached to the water pump I'm not totally sure that the new fan would bolt up to a DI' water pump. That would be the one question I would still have.

Is there any way to test the cooling/flow efficiency of the radiator before I drop $400 on an new one? I really can't decide if it's just the viscous clutch not engaging or if I really do need a whole new radiator... :(