I just got home from a miserable trip from NW Oregon to Calif. The misery was the result of my 98 disco overheating on the freeway. I have never had any issues with overheating before on my disco but when i got inland where the weather is warm and climbed a long hill on the freeway I suddenly saw the temp. gauge climb fast! I turned on the heaters and fired up the fan and was able to keep the temp from going into the red for a while but I finally had to pull over and watch the poor old rover hiss and steam and do a complete overheat! After it cooled down enough to open the refill tank, i was able to scrounge up enough water to fill it up again. I ran the engine with the cap off the fill tank to 'burp' it but never saw any bubbles.
I limped to Calif. and pulled out the thermostat but it still wanted to get too hot every time i climbed a hill. I was able to keep it out of the red by running the heater full blast and made it back home. The weather is generally cool here on the coast and we normally have the heater turned all the way over to the hot setting so i don't know how long this potential for overheating has been there. I suspect a clogged radiator.

I see on old overheating threads that you never bleed the system with the engine running. aside from parking on an incline- how do you bleed it??

 

remove cap on bottle, remove cap on radiator, pass front wheel on a curb or ramp, fill system, wait for warm up( probly gonna loose fluid when it opens) top off, install plug in radiator, level vehicle, top off bottle and install cap

sounds like your clutch fan is not working or clogged rad, or blown hg or a combination whens the last time you flushed the system?

on some vehicles, with no stat the water can run through too fast to cool and with just water or coolant that is not mixed 50/50 you can have problems

 

Thanks for the tips Tom. Clutch fan was replaced last year and seems ok to me. I suspect a clogged radiator.

here the heck is the drain plug on this radiator?

another puzzling thing is the fill instructions. It says on the fill tank ' fill to level when cold"

I assume it means fill to the top of the tank? But that leaves no room for expansion.
those Brits!

 

Here's another question - the clutch fan runs when you first start up the engine making a noticeable whirring sound and then disengages at high RPM. But there is a heat sensitive coil on it and shouldn't it engage again when/if the darn thing gets too hot? I never hear the whirring sound when this thing starts to get hot. Seems to me that would help to cool it back down?

 

there is no drain plug remove lower hose from rad

fill with funnel at the small plug on top of rad or with that plug removed reinstal after burping, full cold is like half way in the resivoir or just below, coolant does flow through it

the loud sound is the clutch fan and it should not be heard at highway speeds or there is a problem with it, idling or driving slow/ traffic yes

do not trust the dash gauge, 9 o'clock or lower is ok, just above 9 o' clock is overheat
use a scanner or buy an ultragauge

some have also reported that while their water pump was not leaking the steel impellor was all ate up on it from non service

 

There are several things you should check.

1. Viscous clutch - spin and release when truck is warmed up, engine off. Should spin, but only part of a turn. If it freewheels, the fluid is gone, swap over is 2000 Chevy Express van, 4.3 liter, w/o AC - about $60

2. Radiator clogged - it is a horizontal row radiator - lower rows are prone to fill up with scale and crud. You can test the temp with an IR thermometer, top to bottom in a vertical line, on the fins. If lower fins colder by 10F then blockage has begun. A small rad shop can un-solder a side tank, rod out the calcium, and flush it, usually $70 or so. New rad is $700 in copper, $235 in alauminum with plastic tanks.

3. Install a thermostat, don't drive without it, it allows coolant to stay in the radiator long enough to get cooled. A 180F stat is a good match. Spring end goes in the block for noobies. My 97 does 183-187 with one.

4. The heat gauge is not real precise. Use a scanner or Ultra Gauge to monitor temp from the OBDII port.

5. The fan blades should suck air from radiator toward block. So a paper towel should be held against radiator by air flow. Including the AC fans when on.

From your info, I would really look at the radiator. It just can't keep up with the heat load.

I bleed by pulling out the radiator top plug (if still plastic buy brass replacement) with truck pointed up hill from a small ditch or hill, with left front up.

 

You state to put left front wheel up to bleed the sys but that would put the fill point lower than the left side of the radiator. Seems like that would hold air that way. Asking for clarification because I did a flush, installed a genuine land rover therm w/jiggle ball at 12o'clock position and still will run hot if I get in any kind of traffic. I am in Florida and it is hot as hell here right now so that doesn't help matters any.

 

You be right, I was backwards, it is the same side as the radiator plug.

Get rid of the Rover thermostat and get a 180F one. If radiator is compromised, it will read more than 10F difference top to bottom on the fins, when warmed up. Enough sludge, and it even keeps hotest air off the fan clutch, which never comes back to full power when needed.

If it won't cool slow, look at clutch, radiator, themostat, and if fans are keeping a sheet of paper sucked against grille.

At the moment mine will make 183-187 on the roadway, even in 95 F; but at idle will reach 207, 221 on a hot day. And that is with a 180 stat. My radiator is sick.

BTW, the stat determines how cold you run. The engine load, and the rest of the cooling system detemine how hot it will get, radiator being a big part of the program. A sludged radiator is just like a lot of guys at places I have worked, it looks normal, but only does half a job, because of what is inside between the ears (well, mounting ears on the radiator).