I have now installed a new 180f stat with no holes. it is now getting up to operating temp at a steady pace as it should but I have verified that Savannah Buzz is exactly right about having some sort of bleed hole or (jiggle device) in the stat and here is why.
The distance between the block and the stat are important for the initial warm up, after the stat opens the first time it doesn't matter were the stat is located, but if it is to far away from the block the water from the block to the stat is much cooler then the water in the block and the hot water coming out of the block has to push through the cold water in the hose to the stat. So the engine temp might be 200f but at the stat it might be 170f. So the engine is getting much hotter then it needs to before the stat opens, when it first warms up.
I will be making some small changes to this mod to get the stat as close as possible to the block and running a 190f stat with a jiggle device.

I will post pics when I am done. and put this one to rest.

 

My t-stat is right on the engine, I run a 195, my engine temp spikes around 210-215 before the t-stat opens.
That is jumping on the highway a mile after starting the truck.
If I just stay in the city and keep my speed under 45mph then it spikes around 200.

No matter what you will get temp spikes until all of the coolant is hot.

 

Keep in mind you are using a digital thermostat (the engine coolant sensor) to measure a mechanical device. The mechanical thermostat will have varying time response. Like Spike says, the first time from a cold start will be a lot higher than what happens as you cruise the highway. Once rolling when warmed up mine will stay within 3 degrees on level ground (we have lots of that around me).

What kind of temps do you get now with the 180, and any more codes?

 

the 180 with no holes was great after it warmed up, it was very consistent at 177-184 and stayed there. it never jumped after it was warm and it never broke 186. However it would reach temps of 225 before opening at start up. when the 225 coolant hit the radiator it would smoke for a second until the electric fan kicked on (which is controlled solely by the temp in the radiator.)

Here is what my problem was, I did not like the location of the stat housing on the original write up so I installed it in the center of the two clips that hold the upper radiator hose to the top of the fan shroud for a cleaner look, and it looked great! But, the distance from the engine was to great, and 225 just scares me.

So I have now placed the stat as close to the engine as possible with allowing room for the Glow Shift Bleeder between the outlet at the engine and the stat. I have also installed a 190f stat with a factory valve in it to release air and cold coolant. (same thing as drilling one small hole in it.) And it is working great! However I think a 190 stat without a hole would work just fine and heat up the engine quicker but would probably reach temps around 210-215 before opening. I will post pics when I figure out how????? so you guys can see the install with part references for the parts I used. I am running a consistent 188-193 after all the coolant is warm. it will spike to 204 and down to 184 until it is all warm but I am very happy with the results.

I could tell a difference in how the truck preformed at 177-184 with the 180 stat and just decided it was to cold. It runs great in the low 190's.

I will post pic's maybe this weekend, I took photos with my Iphone an am not sure how to get them on here, so help with that would be great.

 

Posting pics are easy, especially with the iPhone.
Download the free Photobcuket app, open a free Photobucket.com account, upload your pics.

Scroll over the pic you want and click on the "img code", then paste it in the post you want.



If posting multiple pics put a space or 2 between them.

 

here was the set up I liked the most, as far as looks


only thing I didn't like as far as look was the to much extra slack on the hose clamps, I will be getting smaller ones. This was the setup were the stat was to far away from the block, causing high temps before opening up at start up.

And


I have since bought a new upper fan shroud because as you can see I had already butchered this one before I figured out I did not need to cut it at all. I will post pick of my current set up in my next post.

 

That first pic looks good. Looks like something out of Battlestar Galactica.

 

this is what I have ended up with,

 

My driving is always between 25-35 , 99% of the time here in south florida and I have an ultra gauge ... it shows (slow) residential speeds (which is ALL south florida on the cost side) my 03 DII sits around 203-206.6% and occasionally sitting at traffic goes to 210.2 on the ultra gauge ... never overheating or light from the LR gauge just sits in middle.... anyway.. Ive started driving in 3rd gear instead of D.This keeps my temps at 199-201 while moving and still sitting still at inter coastal bridge for 4 minute or at long traffic light it sits can go to 210 but never higher... usually 206.6-208deg if setting long time.... I did notice a tiny seepage around upper USA driver side radiator under hose but will look closer.. just sitting drip not dripping as I can see but will look closer... anyway are temps normal? I have a new radiator ready to go ( well low milage Im having pressure tested but looks good and 64k miles on it from a parting out disco...

 

The spec for the thermostat is starts to open at 180, fully open at 204F. That about the same (15 - 20 degree spread) for most wax ball (that's what's inside) thermostats. Rover should turn on the electric fan at 212F, and back off when you drop to 202F. So Rover design is happy below 204. The low speed crawl also makes for less heat being blown away, and you running in lower gear increases the water pump speed slightly, making up for the slow "air flow" speed.

But, if it is as much cooling as system will produce in your driving environment now, what about in August?

On a D1, the electric fans run whenever the AC is turned on, which is a help in slow speed. You could consider an electric fan, or a bypass switch to force yours on when you want it. Of course, you could consider an electric fan to replace the one operated by the serpantine belt.

There are also various other sized fans that will attach to your same fan clutch, and various fan clutch units that will attach to you water pump thread. The fan clutch decides at what temp it will bring increased power to the fan. If the radiator, or the tranny cooler / oil cooler, or the AC condenser is full of dirt, mud, leaves, plastic bags, etc., airflow is blocked to radiator, and if blocked in the center it will keep the fan clutch from reacting to higher radiator temps.

Your fan clutch could also be bad. A good rule of thumb is that it should make some "roar" when cold start in the morning, as silicone has settled to one side and it should come on fully engaged. As it warms up and spins the silicone around, the clutch decouples to about 20 % power, gets quieter. At higher temp, it comes back up to a higher power. When warmed up, engine off, spin ran by hand and release. Should not go a full revolution, if it freewheels the clutch should be replaced. About $50 and very DIY, write up in tech section.

A good clean radiator that is not full of Dexcool sludge will keep temps lower. If you have a used radiator, an indy shop can test it, and hot flush out the gunk, pretty cheap. If you put green coolant in a used radiator with Dexcool sludge already inside, you are working against the system.

BP Utah has a water pump that has a larger bronze impeller. Like you operating at higher rpm, the bigger impeller moves more water. The water pump in a Disco is about 2.6 gallons of flow per minute at 1000 rpm, so that is about the whole cooling system thru the pump each minute.

If you replace your thermostat please go with oem, many tales of after market ones that won't open at right time. The stat has little metering holes in the top that mix hot coolant with cold to make stat open. If they are clogged, temp for operation moves up.

The Purple Ice or Water Wetter products can increase cooling somewhat, may even see a difference at low speeds. I've seen it work on some of my old John Deere diesels.

Interesting problem you have, almost all low speed driving, like taxi cab or delivery service.

Pix of Dexcool sludge, thermostat holes, wore out water pump.