Phil,
I used the Devil and had a the same problem. I flushed the cooling system 4 times to finally clear the gunk. The first 2 times I would get good amount of blue gel. By the 4th time it was clear. I also flushed the heater core. The key for me was to back flush the radiator with a garden hose from the bottom up. The trick is to wrap a small rag around the garden hose to seal around the radiator return. I also noticed a large amount of the gel gunk inside radiator on the top side. My theory is that gel is cloging the small radiator bleed pipe that goes to the expansion tank. I flushed the top radiator outlet with a nozzle of the garden hose then backwashed it from the bottom outlet. This is when I got the most gel gunk out. Also check the pressure cap on the expansion tank. I found a lot of gel had filled the grove between the two o-rings preventing the radiator from circulating through the bleed line. Make sure water is circulating back to the expansion tank through the bleed line. With the engine runnng you should see a steady stream flowing into the expansion tank. Once you get all the devil out you should be fine.

Let this be a warning to all Land Rover owners. Stay away from the devil..

 

Well, after a year of hit and miss frustration and Disco Mike on speed dial, I may have found the problem that has been giving me fits. I have been experiencing temp rise at idle. Not all the time and never up to the red, but to the top end of the white. My innova scanner showed as much as 215 and on occasion as high as 225. I got home from work tonight and pulled the thermostat, should have done it a year ago. There are 4 holes in the valve that diverts coolant to the heater core, well, three of the four holes were clogged closed with a sand-like grit. (I tried to attach photos, I hope they uploaded) No wonder the temp climbed at idle. I picked it clean, the stuff was really stuck in there. Once clean, I thoroughly flushed the thermostat and then decided to drill the holes a slight bit larger to see if it made any impact on the temp. Reassembled the thermostat, flushed the cooling system for about 30 minutes and buttoned it all up. Did my best to bleed the system and started her up. I let it idle for about 20 minutes, took the time to wash it while waiting. Then took it for a lively ride and let it idle another 20 minutes, so far, the temp gauge sat right at mid-line. Perfect. I will take it out for another drive tomorrow and see if, in fact, the problem has been resolved. I can't believe this darn issue was a clogged thermosat, but if it is fixed, it was a cheap repair, less the price of the innova, countless hours draining, filling, bleeding, scratching my head til it hurt and then some crying. Word to the wise, following a head gasket repair, replace the thermostat, drain and flush the cooling system, replace the thermostat, it is just a critical part of the system, if it is the slightest bit impaired, it can toast your engine. Thanks for all of the input and advice. I will post a postscript tomorrow. Meanwhile, our 2001 is still up in Salt Lake City getting an almost new 16,000 mile engine out of a 2002 rollover. It has been at the shop since March of this year. Replaced the head gaskets in March and the engine imploded 10 miles later. Have been searching out a new engine since. I bought a guaranted engine in June, sent it to Utah. When they check the heads, it had a slipped liner, engine toast. So I am now into this repair about $3800, don't tell my wife. I could have bought a new motor from Turner at that price. Still trying to get the money back from the guaranted motor......The shop should be done this week. I am heading to Utah next week and will get a chance to try it out, needless to say, I am having the mechanic put a new thermostat in it.......All the best. Phil

2000 DII 138,000 miles (head gaskets at 130,000)
2001 DII 92,000 miles (16k miles on the engine)

 

So far, so good. Took it for an agressive drive on the freeway followed by some around town driving and the needle stuck smack dap in the middle of the temp gauge. I will feel better in a week or so and no temp issues but it looks like it was in fact the clogged theromostat. Keep those fingers crossed. Phil

 

And I thought I was the only one staring at the gauges constantly.
I have this same issue. I would say about once or twice every 3 months or so the temp will rise while idling. This is even after a new water pump w/ gasket. I plan on switching to the green stuff very soon so I will pull the thermostat and check it.

 

Don't check thermostat, replace it, it is one of the cheapest things on a Rover, like $4 - $8. If you don't have a scanner your temp could be moving around a lot more than you think because the gauge gives the same reading ove a wide ange. Might want to check the fan clutch, radiator fins clogged with trash/mud, etc. Those are the cheap parts.

 

Pull the thermostat tomorrow, at a minimum, you will know if that is the source of your problem. Savannah Buzz, the thermostat on the DII is the heart pump style rather than the traditional style like most vehicles. Dealer will charge around 35 dollars. It is a bit of a pain to change, in large part because of the bleeding procedure. It usually takes me about three days to get all of the air out of the system. good luck, I am smiling everytime I drive this thing. The 911 hasn't been out of the garage all week. All the best. Phil

 

My bad, you are most correct. But even at $35, it is still one of the cheapest big impact items in the cooling system. And as you mention, the grief with remove / re-install makes new one a positive idea.

 

I hope you are using a scanner with live data to assess your temps and not just the factory temp gauge. My experience with the factory temp gauge is that it stays right in the middle over a huge range, from about 150-215 it never moves. I've never had the temp high enough to make the gauge move higher, but if you are already having issues the temp gauge is not the best best tool to assess engine temp.

 

I have changed the thermostat in the past so I know it is a small PITA. I just never guessed to look down in there good enough to see if those bypass holes where clogged or not.
I have also been looking into the in-line thermo mod. I see alot of mixed reviews on this though. I live in the deep dirty south so the heater core warm up is not an issue for me. I know that mod cured alot of peoples overheating issues though...

 

I was leaning towards the inline mod if the problem continued. Looks like the issue for mine is resolved. I used an innova 3130 and monitored the temps after the headgaskets were changed and I had the idle temp increase. I sent it up to college with the kids that were driving our 2001. It is still in that truck. I wish I had it down here right now. While driving the temp was very much in the acceptable range, although it was still several degrees higher than my 2001. At idle, it used to climb to 208 and on occasion up to 215 and on a couple of occasions up to 225. That is why I have been so concerned with the temp issue, didn't want to replace the engine. The temp gauge did move rather quickly up when the temp climbed. I can't tell you what a relief it is to have this matter behind me. Now if the engine that is going in the 2001 works out, the Land Rovers will be resolved, at least for the short term. All the best, Phil

2000 DII 139k miles
2001 DII 92k miles (getting a new motor with 16k miles on it)