I've got a stock radiator on the way from salvage. Got a pretty decent price, so long as it's in the condition they said it was. I don't think I'll do any chrome on it though. I just want to get her up and running. I'd like to eventually get the engine bay looking nice and clean, but I've got pretty far to go before I start getting into the beautification phase. Right now I'm still in the 'undo all the previous owner's mistakes and neglect' phase.

 

I thought your problem wasn't leaking, but overheating.
Worst case you may have just bought someone's problem radiator as it could be totally clogged inside, caused their engine to overheat and so they junked their Rover.

Definitely take it to a radiator shop and have it flow tested.
Did you ever look in to a recore? I had mine done for $260 with a heavy duty core and never had any overheating issues after.

 

Here is another for not buying the salvage one. I took mine off and had it backflushed and flow tested. They said it was fine, but took to another shop that did it right and there is partial blockage.

98roverguy bought a radiator from https://www.performanceradiator.com/ and has had good luck with it..

 

Ideally I would have sprung for a new radiator. But I just can't justify the cost right now. I weighted the risks, and decided that the cost savings was well worth the potential risk. I had the unit checked out, then flushed it with water and alcohol again when I got it home. I also cleaned up the temp sensors, and made sure all the hoses were nice and clear. Removed the reservoir and cleaned it out as well. Then, with system put back together, did another flush with water while running at temp for about 10 minutes.

None of this has helped.

I have to admit I'm a little lost at this point. No coolant loss, no white smoke, no water in oil or vice versa. The only odd thing I notice(other than the temperature not staying down) is that no matter how much I try and bleed the system after filling, it seems to keep gurgling from the heater. Also, if you just start the truck and idle it, the heat doesn't seem to work, even at operating temp. I gave it a little gas and held it around 1300 rpm for a minute or so, and the heater began working.
I went looking for the vacuum operated switch that routes hot coolant to the heater core, but it's not where the rave shows it to be.
Not sure where to go from here.

 

Bad water pump.
The impeller is not spinning fast enough to move coolant through the engine and you are overheating because of this.

 

The other thing to check is your belt routing, it can easily be put on wrong but look correct, if it is on wrong the water pump will turn the wrong way and the alternator will not fully charge the battery.
Check the tech section for proper belt routing.

 

The belt is good. Any theories on how a bad water pump would cause this? I mean it's not just straight overheating. It oscillates. Even with the motor operating at a steady state, the temps just keep rising, then falling. The system operates where it's supposed to, but it has these little excursions, then settles back down again. If I drive it, the temps rise higher. If I continue driving it, more and more time will accumulate between oscillations, until it starts to appear stabilized. But that's after like 30-45 minutes, and I've only pushed it that far once.
I considered changing the pump on principle, but I just couldn't picture it causing this sort of thing, and it was a little pricey for trial-and-error.

 

You can get a water pump for under $100 with the gasket, '96-'04 take the same water pump.
The impeller on the OEM water pumps is pressed onto the shaft and can start to slip overtime.
So the impeller can be spinning at the correct speed one min and less than that the next.

If the radiator is good, the t-stat is good and the head gaskets are good and the coolant temp sensor is good what else can it be?
Have you tried to drive it without a t-stat to see if you get the same type of temp spikes?

 

I haven't tried it without the thermostat. I only get a few hours a week to dink around with it, if I'm lucky. So I'm doing good just to get the basic repairs done.
I've got a water pump on the way, so I guess I'll toss that dart and hope it hits the target. I have my doubts about it, but like you said Spike, what else can it be?
Even though I haven't noticed any disappearing coolant or any of the other tell-tale signs, I'm mentally preparing myself for the head gasket debacle. Another forum search produced a guy who was having similar issues, and did all the similar fixes, only to wind up with a cracked head.
I'm crossing my fingers, though, as I really can't afford the time or money to get into fixing that sort of problem.
I have to say I'm feeling the SpencerFitch vibe a little on this. I just got this thing at the end of July, and I've already spent more time with it down for maintenance than any other vehicle I've ever owned. I probably didn't get 100 miles on the thing before this crap started happening. No warning signs or anything. Ran great, looked great, and then "POOF!" Mysteriously busted truck. Awesome.

 

Sorry to hear that you are having such a tough time with the Disco. Was the previous owner having the same issues or do you know?

From what I have seen on this forum, it seems to be pretty common to buy an older DI and then Discover all kinds of horrors that may not have been noted prior to buying it.