I was thinking of doing this at the inlet of the heater matrix.
Or add a 180 degree 5/8”/16mm OD aluminum pipe from the inlet to outlet coolant hoses to complete the coolant flow of the cooling system.

 

Quick update, I no longer have a hiss noise when removing the cap after truck has been sitting overnight. Still have a waterfall sound but seems less noisy than before. I am also still losing a little bit of coolant. I pressure tested the system for 30 mins at 20psi and the gauge didn’t budge and no coolant found any where externally. Checked the back of the block with an inspection camera. No coolant in my oil and I pulled the 7 and 8 plugs to check for steam cleaning. Both looked normal other than a little oil burning in #7 (sandy white ash on the strap).

 

yup tried bleeding more air, still got the issue but im not losing coolant, could be like suggested a heater core thats a bit pluged but i have lots of heat,
kinda bothers me i will get to this one day, i dont want to flush the core as i just put in fresh coolant

 

buy a vacuum filler or go to a shop and have them vacuum fill the coolant. probably would be better to buy one yourself as I'm sure shop rate for an hour or two and the filler would be about the same, or add up to be worth buying for the next time you need to refill the coolant.

 

tempting but I don’t think air is the issue I think it’s something else. I’ve never had trouble bleeding air from a disco

 

I actually did both. Had a shop flush and refill the system for me but they couldn’t get all the air out. I had them stop since the rate was high and the coolant system was no longer “stock” with the inline mod and no bleed screw. I then purchased an airlift system and did a drain refill in my garage with the same result. Still waterfall sound after all that. After replacing the coolant bottle cap now the waterfall sound is much less and I now only hear the sound for the first few minutes and it’s gone for the rest of the drive. If the engine cools back down the cycle repeats.

 

really weird. You have a 2004. Did the 04 have anything different from the rest ? This is a weird mystery My old 04 and my 03 never had this problem with oem cooling system and after I got the inline mod.
my 03 had the waterfall sound for maybe 10 min after I did a coolant change but always bled the air out itself never heard it again
I’m going to research this issue more

 

So trying to do process of elimination

bought a new rad cap Stant 10231 old style 16 psi for a 97 Chevy 5.7

the allisport cap is much heavy duty the spring is way bigger and heavy on the allisport not sure what the psi is

drove this morning waterfall sound still there right around 170 when thermostat starts opening and flow is moving


the one thing I notice about the allisport tank vs the oem tank is that the level on the allisport tank stays near the top

where the level on the oem tank would correct itself near middle and even lower with the inline thermostat


so now I’m thinking if the heater core is a bit plugged at one spot and the flow starts happening when tstat is opening the water pump can be pulling more coolant then it’s feeding on the one spot of the clog causing the sound.

i will have to dive into this more in the next few weeks as I still have a parts truck to strip

 

Nope. The 04 was completely stock when I got it. Only engine modifications I have are, in-line tstat, PCV mod and a snorkel. My cooling system is brand new except for the 5 year old Niesens radiator the PO installed and the heater core which is probably original.

 

I'm about to replace some of my lower coolant hoses, so I'm going to have to do some draining. How do y'all handle flushing the heater core?