There is no theory. Your temps are fine.
what you're trying to do is maintain an lower temp when theres nothing wrong with the 200-208 temp.

You drive, temp drops. You idle, temp goes up a little and the fan kicks on.

Every car I've ever worked on does that.

The problem is when the temp gets too high. Then you have air, a clog in the thermostat holes, bad stat, lack of coolant, or the illustrious "clogged radiator" which almost never happens using green coolant.

 

the inline stat mod does make the system significantly easier to bleed, more like the GEMS and 14cux trucks.

 

Okay so now I am hearing a totally different story than before. It used to be that the OEM 180 degree stat would keep temps down at idle in the 190s. Now multiple people are chiming in saying, no, its fine that the truck gets to 206 (or higher at idle). There are people on the forum that would say that they don't see temps that high and you have air stuck in the system somewhere. Why otherwise would you see temps this high with the OEM soft spring when others don't? Or do you have a clogged heater core?

The "raise the bottle method" where you raise the res with the bleed T open is the one described in rave. Step 9 in the re-fill cooling system procedure says9. Raise the expansion tank approx. 20 cm (8 in)vertically, coolant will drain into the system.

With the inline mod I see temps at the very lowest go to 184. It makes the entire operating range way less in 90% of cases it is 188-193. Long periods of downhill get to 184. Why in the world would it go to 170s or 160s? Its a 180 degree stat. Meaning it closes at 180. Just like the poster above saying that once the stat is 100% open, its open, when it is 100% closed, it is closed. So we would expect to see the same exact temps under thermostat closed situations, which it sounds like we do.

Do you think the theory of drastic heat cycles reducing head gasket life is bull?

 

Actually I did some reading the RAVE and it looks like the temperatures raising at idle is not due to heat soak at all but it is by design of the original thermostat. This is not the way all cars work and this design means that there will be much higher swings in temperature, especially in off road conditions where you might be idling off and on for periods of time.

From Rave:By-pass flow valve

The by-pass flow valve is held closed by a light spring. It operates to further aid heater warm-up. When the main valve is closed and the engine speed is at idle, the coolant pump does not produce sufficient flow and pressure to open the valve. In this condition the valve prevents coolant circulating through the by-pass circuit and forces the coolant through the heater matrix only. This provides a higher flow of coolant through the heater matrix to improve passenger comfort in cold conditions.

Looks like at idle, the thermostat does not allow for coolant to flow through the engine as fast as It could. By design, this leads to temperature increases every time you stop the truck and let it idle. In my case, this was from 188-204/6/8 at every stoplight.

This explains why we all see the same temps when cruising (around 188) because the coolant pump is spinning fast enough to create enough pressure to open the OEM stat. The OEM stat needs 2 factors to open: heat and a significant amount of pressure (based on RPM). A regular stat in most cars just needs temp (and I assume some trivial amount of pressure to open the spring?) However with the OEM stat, you will always see temps at idle rise since the coolant is being bypassed to the heater core and reduced flow through the engine and radiator is present.

I am very curious on the people who report low idle temps (195-) with the OEM setup. Maybe they are better at bleeding? But many on this thread are saying it's actually not that hard.

Well, this is getting a little too internet argument like for me so I in summary I just want to present some facts and people can make their own conclusions. Maybe someone will find this thread when searching for thermostats, bleeding, inline thermostat mods, etc.. and it will help them. If you see any "facts" below please correct me so we can get a mini wiki of knowledge going on here that we all agree to be true.

Summary of Facts Regarding Land Rover Discovery 2 Cooling System

• There are many OEM style thermostats (including the ones that shipped with the trucks in the United States) that run too hot (up to 230f)
  • These should be replaced with a soft sprint / 180 degree stat. Land Rover makes a grey soft spring one or the Britpart 180 is a good choice
  • You should buy an ultraguge / scanguage to monitor temps because with the stock temp gauge, you won't know you are too hot until its too late.
• After converting to a OEM style 180 degree stat many forum posters report that the temps are around 188 when traveling, and up to 206 when idling
  • This temperature swing is because of the design of the factory thermostat where the coolant pump does not have enough pressure at idle to circulate flow fully
  • Many say that this is good enough and is in range and going beyond this level of cooling has no practical benefit.
  • Others say that 206+ is too high at Idle, but lower temps are available with the OEM setup on a 180 degree stat. You just need to bleed better or improve the cooling system
• A more extreme option is the inline thermostat mod
  • This mod (in my n=1 sample size) seems to keep the same lower range temperatures (184-188) but decrease the upper range temperatures (from 206 to 193).
  • Many on the forums say this is not needed and some might argue that it is "too cold" (I don't see how this Is possible since the min temps are the same)
  • This mod eliminates the "bypass" operation described up above and allows for full flow of coolant through the radiator at idle and decreases the idle temps.
  • Anecdotally this is easier to bleed, as all I did was lift the res, open the bleed T and fill it up. I topped off the next time I drove and that was it.

 

The "raise the bottle method" where you raise the res with the bleed T open is the one described in rave. Step 9 in the re-fill cooling system procedure says9. Raise the expansion tank approx. 20 cm (8 in)vertically, coolant will drain into the system.


never had a problem Doing it this way
only trick is when lifting bottle and pouring in coolant you need to add it in slow in intervals. That way air can escape better at a slower rate


by the way every disco is different as far as cooling goes. Different age and shape of rad fan tstat pump etc

keep the temps consistently below 205-210 your fine

 

I'm just joking with the Gods Must Be Crazy thing. If I was at a shop I'd just put a Coolant Vacuum Evac kit on the vehicle and call it a day no doubt the quickest way in the world. In my driveway/shop at home I'm not in a race (also SETX is as flat as a table). As I'm filling the LR with coolant I've always squeezed hoses to burp as much air out as possible (thing of habit now). By the time I'm cleaning up my tools, the LR is warmed up the first time. I turn it off, walk inside, wash my hands, get a drink, kiss the wife, maybe grab a bite to eat, then head back out for the final top off, and crank it back up. This time I check for any leaks, and once I'm satisfied = test drive time and done.

From my experience a lot of issues with gurgling from the heater core = a clogged or nearly clogged heater core (not all the time, but if the system doesn't show low on coolant or isn't loosing any I always check the core). When my 02 Kalahari started to gurgle around June several years ago I feared the worse lol (as it had 230K on it at the time). Checked the coolant level and it was fine. So I decided to add the clear pyrex tube to the system to see if I had air indeed circulating thru the cooling system and nada. Also the gurgling had gone away as quickly as it had started... Well I had driven 3hr to a friends party and while there a serious cold front came thru and the temps really really dropped. Well I left the party around 3AM and when I turned the heater on I was like WTH when it was stone cold. Then it hit me!! The gurgling wasn't from air, it was from the core being clogged. Being as OCD as I am when it comes to my LR's I just had to pull over and verify. Sure enough one heater hose was nice and warm while the other one was no where near as warm. Problem solved!! Got home crashed for a few hours, and then I set to work on the Kalahari. I very carefully cut off the old heater hoses (so I didn't damage the core). I put a garden hose on one of the inlets, and it it barely flowed out. So I reversed the flow and a huge ball of white snot blew out. I ran the hose in that direction until it ran clear. Then I put the hose on the other inlet and verified the flow was identical to the other one. I then ran into town for some 5/8 heater hose, cut it to fit and installed it (in/out does not matter as it's just a closed loop) and I went straight in/out vs cross em. Heater works flawless and that was nearly 3 years ago!

The one thing I did always like on the older RRC 3.9/4.2L engines = the tall metal tube that was inline of the heater hoses to get the air out of the system. I wish they had honestly left that on all the LR V8's.

 

Not exactly.

The original setup puts the thermostat on the cool side of the system, or the output of the radiator, with the T fitting dumping hot coolant onto the stat.

When you add the inline stat it puts the thermostat on the input or hot side of the radiator.

The temp sensor is reading the hot engine coolant, not the cooled coolant as it enters.

Youre basically making the engine like every other old American V8 that had a thermostat on the intake instead of how many foreign cars are designed.

I do get my temps low 190's with spikes to 201.

If you think rover techs at the stealerships sent out Rovers that didnt go to 206 you're crazy.

206 will not kill it and if you think there isnt pockets hotter than 180 with the inline you're crazy. It's only 180 at the sensor.

Does the inline make it run more steady? Sure but it's not the same type of system as was originally designed.

Modify away.

I'm just suggesting that running a rover with acceptable temps with original equipment isnt that hard.

 

On my 14th Disco, always do the inline mod. Temps usually range from high 170's to high 180's, low 180's on the highway. Removable for testing with no loss of coolant.

 

I’m firmly in the “inline” crowd. It’s simple and now my 4.6 Ltd D2 has similar engine operating temperatures to my D1. (184-194)

I did this after fighting overheating for years, especially off-road. With a brand new stock cooling system and the td5 genuine stat, it was easy to get my D2 to 230 degrees when off-road in low range. Now I don’t see anything over 200. Ever.

Theres pros and cons to this type of modification, but I sure don’t miss the “octopus” mess that is the Bosch D2 lower hose design.

 

Britpart 180F (78C Stamped one), and off road in TX in low range 188-209F tops. The 209F was sitting still at idle down in a creek bed. Get rolling in 2nd (manual mode engaged) and with higher RPM's 2200RPM range I was instantly at 188F. It's all about air flow, and we only have so much room for air to flow. Until someone makes a 4 row radiator, that will never really change.

I know for a fact D2's from the factory were running 220F and up. I had 2 03's and I'd sit at the beach idling or out on the trail and the thought of overheating never crossed my mind. However you could tell they ran hot as plug wires had a very short life, and a lot of loom under the hood died quickly. Yet with all that both my 03's got up to 160-189K and never had their HG's touched. 188-215F is perfectly fine operating range. The engine was tuned to run optimal at certain temps. You lower that temp to much and HP, MPG, and emissions will suffer.