The reservior is just about empty in the video, so it can not be coming from the reservior itself. It has to be coming from the return line from throttle body heater, since it enters the cap area at the overflow tube area. You're basically, pumping anti-freeze out of the system. Get what you're saying about needing to turn it a full turn...to get the sensation that it is a little loose. Normally, do the one turn to loosen...then tighten it about 3/4 of the way, stopping before it gets that "tight-feeling"...which leaves it about a quarter turn loose. That's what works for me.

 

I run mine one full 360 degree turn from full tight to intentionally prevent the system from building any pressure. Over the years I have split hoses, radiator end tanks, reservoirs, thermostat Y's, and had hoses start leaking out from under the clamp. All bad on a long drive as then your coolant is on the ground, not in the engine. In addition a pressured cooling system increases the probability your head gaskets will leak if you do have an overheat. I have seen gaskets blown to the outside, water pump gaskets blown, and front cover gaskets blown, none of which can happen in an unpressurized system.

The only advantage to a pressurized system is that it increases the boiling temperature from around 220 to about 250. If a disco ever gets to 220 you already have some pretty big problems and 250 with pressure is going to make it much worse.

Unpressurized does also help vent any combustion gases on the off chance you have a small hg leak - prolongs your ability to drive it. If you pressurize and blow a hose of your day is over in like 5 minutes.

You can bypass the throttle body heater as long as you don't live in the great white north, I think everyone in the lower 48 does with no problems. You should be fine in the Los Padres National Forest.

Advance Auto rents the pressure tester, that is an excellent tool for finding your leaks.

 

Please keep in mind that the boiling temperature reduces with altitude. At 10,000 ft altitude by about 20 deg. F, since the ambient air pressure is lower there. This is true for both, non-pressurized and pressurized (since the pressure relief valve works relative to ambient air pressure ) systems, but a non-pressurized system leaves you a way lower margin at high altitudes.

 

Solid point. With some rare exceptions elevation has the benefit of also dropping the ambient air temperature such that the cooling system works better. I used to live and wheel in the Sierra's and in/around Flagstaff and even in the summer at 10k feet the ambient was around 70. I assume there could be locations in sourther AZ or the middle east where that is not the case.

 

I’m not a scientist but the drop in air temp with altitude is because it has lost density. Thinner air won’t absorb the heat from your radiator as readily as more dense air, which I suspect more or less cancels the positive effect of the cooler air.

 

Thanks everyone - I'm only at 3,000 ft elevation and the highest peak here is about 4000'. I'm in no position to go anywhere near 10,000'. I drive down to about sea level and back up pretty regularly (life has been irregular since last March).

I've noticed the oil level dropping slowly since I changed the oil about 1-2 months ago. I checked the oil plug bolt, which has a washer and I checked the oil filter, which I tightened by hand, but it seems fine. The other day, I started the engine with the hood open and didn't see it pumping out like the other time. I topped up the level beforehand as well and I keep coolant in the car.

It's been about 4 years or so and I haven't changed the coolant (going to need to learn how or take it to a shop because I don't want to have to dispose of the coolant and they'd probably better equipped to handle that. I just don't know if that's a waste if there are other issues. I'm not sure what the first step here should be, but I'm hoping it's not a major problem... I'm worried that putting pressure through the cooling system could damage things, but I guess if they're on their way out, that's going to happen anyway and better know sooner than later.

I could replace the expansion tank since it looks pretty yellow and could be problematic. Are the genuine parts the best or are there any aftermarket parts that might do a better job?

Do you recommend that I flush the coolant and try again with new fluid? I know people say not to use anything red. I've been adding generic green fluid and that's what was put in there when my brother had the radiator and hoses replaced about 5 years ago.

I don't know what to do first - flush coolant and replace? Extinct's thermostat modification? I was hoping to deal with my power steering pump, but this is much more important, so I wouldn't mind work on that project next instead. Pressurize system and check for leaks? Then, replace expansion tank?

 

3,000 ft is not a big problem. In Colorado or California the situation is different (there are paved roads up to 14,000 feet).

 

Yeah I'm in California, I meant the highest peak in my immediate area is 4000'. I'm not going up higher than I have to anytime soon. I've got to figure out what's wrong here.

 

Exactly right, but what we're talking about is the offset. We know that the discoverys cooling system is capable of holding about a 100 degree temperature difference from Ambient at sea level. So if you go up to 10,000 ft and the density of the air drops reducing the radiator efficiency but at the same time the temperature of the air drops increasing the radiator efficiency the the two effects basically cancel each other out and you wind up at the same place you started except with a lower boiling point. So I guess if you're working your disco hard at 10000 ft maybe you should tighten the cap so that you've got a pressurized system, but then again I don't ever let mine get close to 200 degrees

 

What do you guys recommend?