It will idle all day long without overheating. I was running the cap one turn loose, but I tightened it the other day after checking for any air in the system.

 

The only component that is not new is the heater core

 

You most likely have a radiator issue. i have had customers put brand new radiators in that were clogged. You can check this by removing the thermostat element from the housing and go for a drive. If it gets hot on the highway with no thermostat then it is the radiator. Getting hot idling and highway is thermostat. Getting hot idling only is clutch fan.

 

Extinct, I've seen you advocate this before. What's the basis for recommending it, other than avoiding cooling system leaks that would manifest themselves if the system was operating at pressure? The system is designed to operate pressurized. Seems like a band-aid.

 

If I recall correctly, and he will correct me if I'm wrong: Loosening the cap lets a little pressure off an older over-taxed cooling system. At 1/2 turn loose it's only going to boil over at 230° at which point you're already hosed..... So why not save a little pressure?

 

We all know from experience that as DIsco engines get hotter, the probability of blown hg and warping the heads go up. This is mostly because the aluminum becomes more ductile with temperature and the pressures inside the cylinders goes up and depending on what is going on so does the potential for the cooling system pressure. Also as temperatures go up the plastic and rubber in the system gets more ductile, so the probability of those failing if the system is under pressure also increases. So lets keep that in mind during this discussion

The basis is my considered analysis of the benefits versus the potential negatives of running pressurized system versus an unpressurized system.

On the benefits side of a pressurized system:

1. it raises the boiling point of the coolant from 228 degrees to 268 degrees. However, this is only a benefit if the engine is going to be operated long term at a temperature of greater than 228 degrees. I have the unfortunate experience of operating a Disco engine in the 230 degree range for short periods of time without blowing the HG (due to not running the cap full tight). However I doubt very seriously you could operate a Disco engine much hotter than that for any significant period of time without blowing the hg. So if I have a pressurized system, I can operate at say 250 for an extended period of time. At 268, the coolant will boil and the pressure will increase in the cooling system, hopefully opening the pressure relief valve in the cap and allowing the pressure to escape before another component fails. If we continue operating with whatever is causing our system to run at 268 degrees we will eventually boil the coolant away, however assuming we have a full cooling system that will mean boiling off around 2 gallons of anti-freeze.

If you can think of any other benefits of a pressurized system feel free to add them here. I suspect pressurized systems came in to being when cooling systems were metal and ethylene glycol coolants that boiled at 228 degrees were not a thing yet.

On the negatives side for a pressurized cooling system:
1. System pressure is more likely to crack any non-metal components. I have cracked or blown hoses, radiator end tanks, coolant bottles, and lower wye fittings. I have even seen a factory thermostat split in to two during an overheat (not my truck).
2. System pressure is more likely push coolant out from under spring type hose clamps or push hoses off of the connected fitting even with a screw type clamp.
3. System pressure is more likely to blow the headgasket when operating at higher temperatures, either interior or exterior blows.
4. System pressure will force coolant past the seal keeping coolant out of the water pump bearing once the bearing begins to wear a little, we see that as water out of the weep hole but it hastens the demise of the water pump bearing.
5. If the system is running with the pressure cap full tight, and an overheat condition occurs to cause the coolant to boil, pressures will quickly rise to a level that will exceed the pressure caps ability to relieve. Causing 1-4 to definitely occur.

On the positives for a non-pressurized cooling system:
1. None of the negatives for pressured numbers 1-4. Quite simply it becomes almost impossible for any of the non-metal components to fail.
2. Lower boiling point of 228 degrees. What this means is if you do have a truck running hot, it will start boiling the coolant at 228 degrees. Boiling water absorbs 540 times as much heat as it takes to raise it one degree, so once we reach that temperature a tremendous amount of energy is being dissipated. Further, much like a pot of boiling water on a stove cannot exceed 210 degrees until the pot is empty of water, an engine full of coolant cannot exceed the boiling temperature of the coolant until it is empty. This means that the engine temperature cannot physically exceed 228 degrees. This is a much more survivable temperature for a Disco engine. If you operated it for a long period of time at temperature it would eventually boil the coolant away, but that would take a long time, likely hours.
3. Coolant can be easily added even with the engine running at temperature by removing the cap and adding coolant without fear of a coolant eruption.

On the negatives for a non pressurized cooling system:
1. See positives for a pressurized cooling system
2. Due to the design of the D2 cap and bottle neck, a small amount of splash overflow may occur and go out the overflow tube. I eliminate this by running a hose over the overflow tube up to the cowl area. Initially I ran it up under a pillar with the end poking out in the field of view so I could watch it but after watching it for more than a year I realized it never overflowed and I don't worry about it anymore.
3. Slight coolant loss due to evaporation. I consider this to be a cost of operation much like oil or fuel. Maybe a quart between oil changes? So about $1 for 5000 miles?

I have never blown a HG nor a plastic component once I started running non-pressurized, and I have pushed several to 230+ towing.

 

Update: The temps swing from 177-210 up and down. The temperature climbs up then back down continuously . It actually does this at idle and at highway speeds. So I guess that I need a new thermostat.

What can I use locally until I can get a high flow from you?

 

Have you removed the thermostat element from the housing? You can use any standard small block chevy thermostat, just need to drill 1/8 hole in it for bypass.

 

I haven’t removed it yet. Even though the temp swing is wild it still does not overheat. I will wait for the thermostat from you.

 

I don't think it is the thermostat element, they don't work that way. I suspect you have something else going on. The thermostat element opens and closes due to thermal expansion of a wax inside the element bulb. That wax expands and contracts with temperature. You engine including the coolant and motor oil and everything bolted to it has a lot of thermal mass and it cannot quickly change the temperature of all that mass. About the fastest it can happen is pulling a heavy load up a steep grade where you are basically full throttle for long periods of time. Or conversely coasting down a long grade after pulling the grade and you are out of the throttle for a long time. Even then, it goes up and down relatively slowly. If you are seeing quick swings you either have gas/air in the system at the sensor that is causing it to swing wildly or your sensor is going out. This is why many people myself included run external gauges that less susceptible to those sorts of swings. The factory sensor is in a location that if you have air in the system or a blown hg putting gas in the system it can read that as crazy temp spikes. Even if the temperature could change fast, the thermostat element doesn't move fast. You can see this with a test going from boiling water to cold running water, it still closes pretty slow and even after it woudl close it would take a while for the engine to heat back up all the coolant and motor oil and metal thermal mass.

Not that having a spare thermostat is not a good thing, it is, but I highly doubt a different one is going to change what you are seeing. Did I already send you one, or do you need me to? Did you email me? We get a lot everyday and not everyone emails or orders using their forum screen name (although some do).