I dont believe so, it just allows better flow past the thermostat.

 

Umm you are kind of proving my point here. The fact that the effective bleed solution requires a multi-day effort and parking on a steep incline to me means that an alternative solution is viable. I know no one here is arguing against the inline mod, but you have to admit people chiming in with "the OEM works for me" after doing some crazy bleed procedure, doesn't paint a full picture.

I do appreciate the discussion though. Thanks for the data and ideas.

 

I have 3 D2's and I've never had to perform a Gods Must be Crazy maneuver by winching it up a tree to get the air out of the system.



I do whatever repair is required to the cooling system, fill it, run up to temp (195F usually) shut it down, let it cool, top off coolant reservoir, then open bleed screw and fill from there. Then restart the engine and let it get up to temp. After that you should just be able to top it off at the reservoir, and the T and call it a day.

 

Seriously. Some of you are completely over exaggerating how difficult bleeding the cooling system is. I have done it on flat ground without issue.

 

Okay then what gives? Ive tried 4 different thermostats with the bleed proceudue described here:

1. Fill with res raised up above until coolant comes out the bleed T
2. lower the res, top up the T
3. Run the truck with the heat on
4. let it cool 100%, top of the T when stone cold
5. Repeat steps 3 and 4 every day for a week, with raising the front on a curb

Doing this multiple times with multiple stats (grey soft sprint, Lucky8 180, Britpart 180) always had idle temps up to 208. As soon as I installed the inline mod, the idle temps are 188-193.

So what's your theory? It either has to be a series of bad stats or its quite difficult to bleed. The truck obviously has no issues with the inline stat.

 

Depends on how long the idle times are and outside temps. It's not uncommon for temps to continue creeping up like that no matter what thermostat you are using when idling for extended amounts of time. Heat soak is a bitch on these. The water pump isn't spinning fast, neither is the fan and that heat doesn't have many spots to escape. I have used stock, 180, and as of last night even a 172 degree thermostat and have experienced temps climbing above 200 and even 217 at most no matter what on HOT days with long idle times. Thermostats only allow coolant to begin flowing through the radiator fully at a certain temp, so you will notice the cooling system working earlier or later as a result, but the design of the entire cooling system has its limits. I haven't tried an inline type yet, but would be willing to bet it isn't exempt from heat soak. Vehicles with electric fans don't have as much of an issue as the fans can turn on at a given temp and move a ton of air, where as an engine driven fan is limited in it's speed and volume of air it can move by engine RPM.

 

Yep that's the only real advantage of a properly configured efan with enough airflow/power. Most modern cars with efans = it spins at a normal RPM say while you're driving. Then when you stop at idle it goes off the temp sensor & will then spin the efan at a max speed which if configured properly is enough to keep it cool even at higher temps.

The fan clutch tries this but yep it's based off engine RPM more vs a temp sensor. However add on efan kits are not really on par with the OEM setups. As the controllers aren't wired into the ECU (to take account for HVAC use for example). The shroud has to be designed properly to still allow good air flow thru the radiator vs creating hot spots, and the fan without a shadow of a doubt needs to be most powerful you can get and the biggest. The 3rd party controllers also can fail leaving you totally dead on the side of the road.

I tried several efan kits for various 4x4's over the years Jeep/Hummer, and in the end the fan clutch setup was much much more reliable! On the Jeep/Hummer setup adding a puller efan like a D1/D2 config helped a lot. On our D2's the radiator is rather small so more rows would certainly help like a 4 row.

When you have trouble getting the air out you really need to inspect the heater core, radiator condition, or if all else fails remove the block plugs and see if you can get any kind of trapped crud out.

The other option is to put a vacuum kit on the cooling system to drain it, and then use it to reverse fill the cooling system = no trapped air. I've just never needed to use one.

 

I 100% agree with the theory you have proposed and it sounds good but it does not match with my experience. I totally agree with the idea that once the thermostat is 100% open, there is no "more open" but my experience does not line up with the idea that the bypass stat was fully open. With the OEM stat, I have sat on a highway full of snow with the temps in single digits and watched the truck climb up to 204, 206, 208.... and I turn it off while I was waiting for avalanche control up ahead to clear.

After the inline mod, I wanted to see how high the temps would get so I sat in my driveway, in the sun, about 80f outside, the AC on full blast for about 15 min and it actually went down from 193 to 188 after it reached some sort of equilibrium. I even turned off the AC to see if would make a difference since I think it spins a fan, and it didn't. There are a lot of posts with people who see 204-208 at idle after bleeding with the OEM stat and people just assume they must have air in the system. I really don't know what it is. Maybe with multiple directions for the coolant to go with the bypass style, not enough pressure / flow is sent to the top of the radiator to keep everything circulating quickly enough to keep it cool?

You'r "the thermostat is 100% open" theory suggests that the truck would run at around 200+ with no thermostat at all? Do you think that is true? I really don't know.

Water pump, radiator is new and block was just rebuilt 18 months / 10k miles ago so I don't think things are totally gummed up. Only thing that could be to blame I guess is the heater core.

All I know is I tired every trick in the book to bleed with the 180 stat and the temps wouldn't come down at idle, and I have seen a lot of posts a similar story. I remember one guy who had a brand new Turner motor and it kept overheating and he had to cancel taking his Disco on the trip.

It does seem like that some people have good luck with the OEM setup but I find it so reassuring to watch the temps stay low and not fluctuate too much. I drove about 2 hours to buy a Baja Rack (and another Disco attached to it) and it was crazy seeing the temps go from 188 cruising, to 190 at a stop light, then back to 188 when moving again. The fact that the temps are much more stable vs OEM (even for people who have lower temps that I did) suggest something funky is going on with the pressures/ flow.

It is an interesting problem.

 

Crazy?

You park on a steep hill and squeeze some hoses. Takes 15 minutes and I did it once in the last year.

There is another procedure which involves the bleed screw that takes awhile.

Then there's the raise the bottle method.

When I coast down hills my temps drop to the low 180's. With the inline mod, what do they drop too? 170's, 160's?

Its your truck, put whatever parts on it you want. I'm fine with my temps being the intended temps 190-206.
230,000+ miles and still going.

 

Too much time. You dont need to winch it up any tree, you just park it engine facing up a hill and let it run. Rev it, squeeze the hoses and the air comes right out. 15 minutes and you're done.

Or heres an even better idea.
When you drain your cooling system and you have to fill it back up, make sure the truck is high in the front and you wont have much air to begin with to even worry about.