KV6 Top Hose Pressure

MGtom91 · 18th June 2021, 18:51

On my 2.5 KV6, did a full coolant drain, heater matrix flush (cold passenger side vents), new thermostat kit and expansion tank cap from DMGRS.

Coolant refilled and bled, unblocked the coolant bleed ports on both manifolds as they were blocked, heaters nice and toasty both sides and temp rises normal until fan kicks in. Top and bottom rad hoses both hot when stationary as normal.

I noticed something that is concerning me when I was bleeding system. Followed the official bleed procedure to the letter, lifting tank up etc and ran system with cap off until around 82 degrees, at which point coolant started to rise up the tank so I screwed the cap on. At this point the top and bottom rad hoses were red hot but I could still squeeze them easily. As soon as the cap went on, both hoses started to pressurise and after about 5 min, both hoses are solid and cannot be squeezed (they don't bulge, just rock solid) and feels like they are over pressurising. Don't know if I'm being paranoid??

Could this be trapped air, would the hoses visibly bulge if there was too much pressure, would the cap vent any excess pressure whether steam or trapped air before the hoses explode ?

No excess pressure left when taking cap off once cooled down and coolant level is on max below the fins of the tank.

How hard do your rad hoses get at normal operating pressure, should they be as soft as they are to squeeze before the cooling system starts heating up and pressurising ?

T-Cut · 19th June 2021, 07:25

Hello Tom, the cooling system is designed to run under pressure. This is created primarily by water vapour due the increase in temperature of the coolant. Trapped air in the system will also contribute but the bleeding ritual should take tare of that. The header tank cap/pressure cap is designed to limit the running pressure to about 22psi. This means all the hoses in the system will be pumped up to this sort of pressure when the engine is hot. If the temprature raises the vapour pressure above 22psi (due to an overheat event) the pressure cap will vent off the excess. So, a hose pressurised to 20psi or so feels pretty hard.

If the pressure cap is new and it doesn't release any pressure when the engine's hot and ticking over, I doubt there's much to worry about. The standard pressure cap is marked '140'. This signifies 140 kiloPascals release pressure and equates to around 1.5Bar or 22 psi.

TC

18th June 2021, 18:51	#1
MGtom91 Regular poster MG ZT KV6 (160) Join Date: Feb 2018 Location: Solihull Posts: 36 Thanks: 0 Thanked 6 Times in 6 Posts	KV6 Top Hose Pressure On my 2.5 KV6, did a full coolant drain, heater matrix flush (cold passenger side vents), new thermostat kit and expansion tank cap from DMGRS. Coolant refilled and bled, unblocked the coolant bleed ports on both manifolds as they were blocked, heaters nice and toasty both sides and temp rises normal until fan kicks in. Top and bottom rad hoses both hot when stationary as normal. I noticed something that is concerning me when I was bleeding system. Followed the official bleed procedure to the letter, lifting tank up etc and ran system with cap off until around 82 degrees, at which point coolant started to rise up the tank so I screwed the cap on. At this point the top and bottom rad hoses were red hot but I could still squeeze them easily. As soon as the cap went on, both hoses started to pressurise and after about 5 min, both hoses are solid and cannot be squeezed (they don't bulge, just rock solid) and feels like they are over pressurising. Don't know if I'm being paranoid?? Could this be trapped air, would the hoses visibly bulge if there was too much pressure, would the cap vent any excess pressure whether steam or trapped air before the hoses explode ? No excess pressure left when taking cap off once cooled down and coolant level is on max below the fins of the tank. How hard do your rad hoses get at normal operating pressure, should they be as soft as they are to squeeze before the cooling system starts heating up and pressurising ?

19th June 2021, 07:25	#2
T-Cut This is my second home Rover75 and Mreg Corsa. Join Date: Nov 2006 Location: Sumweer onat mote o'dust (Sagin) Posts: 21,753 Thanks: 341 Thanked 3,660 Times in 2,924 Posts	Hello Tom, the cooling system is designed to run under pressure. This is created primarily by water vapour due the increase in temperature of the coolant. Trapped air in the system will also contribute but the bleeding ritual should take tare of that. The header tank cap/pressure cap is designed to limit the running pressure to about 22psi. This means all the hoses in the system will be pumped up to this sort of pressure when the engine is hot. If the temprature raises the vapour pressure above 22psi (due to an overheat event) the pressure cap will vent off the excess. So, a hose pressurised to 20psi or so feels pretty hard. If the pressure cap is new and it doesn't release any pressure when the engine's hot and ticking over, I doubt there's much to worry about. The standard pressure cap is marked '140'. This signifies 140 kiloPascals release pressure and equates to around 1.5Bar or 22 psi. TC Last edited by T-Cut; 19th June 2021 at 07:30..