Hi Extinct,
Got the inline kit, thanks for sending. I haven't had a chance to install yet. I had a question about this suggestion - I recommend running it one turn off of full tight to prevent building pressure and blowing hoses or radiator end tanks (frequent issue on 15+ year old hoses).
I thought with a pressurized cooling system you need to keep things tight and under certain psi to work correctly and the cap relieves excess pressure at 20 psi. On mine if there is any leak of any size I get a small amount of coolant out of the overflow tube. I keep a cup zip-tied under it so I can monitor if any coolant is being forced out. Without the cup it all evaporates on the chassis and you don't know if its leaking unless you see it. So far this works great as I have found three small leaks using this method including a small invisible crack in the reservoir tank. Once the leaks are fixed, overflow drips stop immediately. I think the cap/tube is designed to relieve any pressure over about 20psi. I might be wrong.

Not-a-inline question - I know over on another thread you mentioned using a speedi-sleeve. I am about to use one on my harmonic balancer for the front seal. My question is of you pressed it all they way down and left the flange on it. It's pretty narrow and only allows for a few mm either way to center under the seal.

Thanks in advance

 

So the recommendation on running the cap loose come from a couple things:

1. With a fully pressurized system, any flaw magnifies the serious of the potential leak. Over the years I have cracked caps, radiator end tanks, lower radiator hose wyes, blown hoses, had leaks come in under hose clamps, etc. The nature of the Disco cooling system is such that unless you are towing, pulling a grade, or in hot weather it won't overheat until it has no coolant left then of course it goes to 300 degrees in moments, blowing the HG in the process. Also if you have a high mile truck it accelerates the deterioration of the hg seal at the water passage. Yes, the cap is designed to relieve at 20 psi.
2. You cannot easily remove the cap hot once the system is pressurized. You will get a face full of coolant and burned badly. Learned the hard way.

The only benefit to the pressurized system is that it increases the boiling point by 20 degrees from 230 to 250. If a Disco every gets to 230 you already have bigger problems.

Running one turn loose has no other detrimental effects and places less stress on all the components, I run all my trucks that way (6 in the yard at the moment).

Re: speedi sleeve - you can leave the flange on if you want, no detrimental effect as long as you put the flange on facing the balancer of course.

 

Thanks for that and makes sense. As you said the pressurization does seem to magnify any small leak. That's what I have noticed. So keeping the cap backed off a turn does not act like a leak itself because of the way the reservoir is designed correct? In other words the cap/overflow chamber is not the same as the rest of the tank/system in terms of pressure. I keep meaning to take my old one apart to see how it works inside.

 

A slightly loose cap keeps the pressure from building as high, as Extinct stated this lowers the boiling point and your coolant will boil more quickly than a tight cap, but it has no practical negative effect because if you ever hit 230 on a Discovery you already has all the issues you'll get a 250.
Coolant shouldn't leak from the cap as it's at the top of the system and not in direct contact with collant unless the coolant is boiling and if it's boiling you already have an issue.

Even in the care case of a cap leak that's better than blowing a hose and bumping coolant so fast you can't respond.

 

Exactly this. You will get no leaks with the loose cap as long as the system is healthy.

 

Got the thermostat installed. Went pretty easy. At first go it went up to 210 and I shut it down. The coolant tank level did not move at all. Tested the thermostat and had a beer. I guessed airlock. I then poured coolant down the hose that goes into the manifold off the the thermostat until it ran out. Reinstalled and left the radiator hose unclamped from the housing but on. Started the truck and let air out of the hose until it appeared more coolant was coming from the bleeder hole in the t stat. Hooked all back up and now works well. I haven't seen over 190 yet. Takes forever just to get to 180. So far the temp actually drops at idle vs go up. Nice work Extinct!

 

I guess SETX is just HOT.... With inline I'll still reach 207F cruising down the road at 80MPH. It was around 80F but humid. Later that evening on the ride back it was 190F.

 

Hate to say it but I think you have a problem somewhere else. Made multiple road trips last summer in my 00 with 250k, always held 100 degrees over ambient no problem at 75 mph. Had one of the guys last summer with a brand new radiator that was bad, it was only after he ran the system with no thermostat at all installed that he finally realized he had a bad radiator - put a new on in and instantly went down to 100 degrees over ambient.

 

Everything else is in excellent shape, new water pump, new hoses, fan clutch is working properly HD unit, no coolant loss, no excess pressure on hoses, radiator is clean n clear, heater core is flushed and flows fine. With OEM setup I never saw past 215F in the hottest summer months off road or stuck in traffic (206-209F was the average). This was across 3 D2's with 180F thermostats when they all had the same setup. Now with the inline when it's cooler weather outside it takes forever for the 02 to get up to temp, and it wouldn't pass 184-188F no matter what the speed. Now that it's warmer out and humid as can be (concrete is sweating like crazy) as it's been going from cool to hot like it just can't make up it's mind I am seeing a constant temp of 207F at 80MPH. Once you slow down to the sweet spot which I have found out to be 55-65MPH temps (on all D2's regardless of inline or OEM setup) will drop to under 200F quickly. Then if you cruise with hardly any throttle input say 40MPH it'll go down to 188F.

Since switching to the inline setup I have driven the same trip/route for several weeks now. Same exact results without a single spike or fluctuation. If there was a problem it would not stay consistent like that. You've also got to remember the 02 D2 has a TF Bumper with a Warn winch installed, along with the TF lower skid plate which angles up into the TF bumper. We all know the D2 has a tiny radiator surface area, and blocking it with an aftermarket bumper, a winch, and a skid plate = will change the air flow a lot vs a stock setup.

For example I crank her up, and it if I leave it with the HVAC on full blast at idle it will sit at 195F for an hour. Hit the road say at 1:30PM once again with the HVAC on full blast (road temps are at their highest) merge out onto I-10 at cruise with traffic which is usually 75-80MPH and temps will go 195-200-207F, slow down on the exit ramp and it'll get back down to 195F sitting in traffic. Now fast forward to 5:30-6:30PM, same exact trip in reverse (headed home) on the same road, same speed, same amount of traffic, and it won't go above 190F. That tells me it's not the vehicle but the ambient temps outside. Now I can jump into my 99 D2 with the 180F Grey OEM LR Thermostat, cruise at the same time, and return at the same time and it'll top out at 204-206F on the way there, and 193-195F on the way back. However with the OEM setup I can not sit at idle for long because it will climb. D2 #3 the 04 with SAI sets a P0126 fault constantly with a 180F OEM style setup. It will cruise at nearly identical temps as the 99 D2, and once again if you sit at idle it will eventually climb. The inline setup can handle idling MUCH MUCH MUCH better vs the OEM setup.

 

Ok, did not realize your bumper setup was affecting the airflow. That explains it. I did notice about a 5 degree temperature drop on mine with the Saudi grille, running that now. I run electric fans on my winch truck with a thermostatic control on it, never sees the high side of 195, the fans come on at 190. In mild weather the fans don't come on going down the highway.