Coolant top off

[philo_beddoe]

Should the coolant be right up at top off when you open rad cap on a cold engine? Also, why does upper rad hose collapse as engine cools? Then of course it goes back to normal at start up.

[1967KaiserM715]

Any overflow tank?

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[bd]

With coolant recovery systems the radiator should remain full to its very tippy-top (no air).  Coolant is added to the recovery bottle to maintain the level between the ADD and FULL COLD marks.  If there are no leaks in the 1/4" tube connecting the radiator to the recovery bottle, and the recovery bottle isn't empty, either the radiator cap is faulty or it's the wrong style.

[philo_beddoe]

I have an overflow tank. Its at the "full" line, couple inches from the bottom. I guess im good.

[bd]

...why does upper rad hose collapse as engine cools? Then of course it goes back to normal at start up.

...either the radiator cap is faulty or it's the wrong style [cap].

I have an overflow tank. Its at the "full" line, couple inches from the bottom. I guess im good.

 

The coolant level maybe okay, but the upper hose collapsing is probably due to the radiator cap vent valve not opening when it should to allow the coolant free return from the recovery bottle back into the radiator.  Either that or the vent in the coolant recovery tank cap is blocked.  A kinked recovery tank hose is another possibility.

[philo_beddoe]

I got the rad cap from VileZambonie, i think its an oem cap. Those caps have a vent valve? I thought it was a sealed system.

[bd]

Closed system radiator caps have a pressure limiting valve that prevents excess pressure buildup from coolant expansion in the radiator (the pressure rating embossed on the cap), but they also have a second valve (a check valve) that normally closes under pressure, and then opens as cooling system pressure drops below barometric causing a suction to develop from coolant contraction.  That check valve allows coolant to return from the recovery bottle back into the radiator.  The migration of coolant back and forth is what makes it a "closed system" and maintains an air-free cooling system.  If you remove the cap while the engine is cold and just look at it, I think you will begin to see how it works. 

Well, if the check valve sticks closed, or there is a blockage in the line between the radiator and the recovery bottle, or the recovery bottle is not properly vented to atmosphere, coolant will not return to the cooling system as it cools and the radiator hose can collapse.  As long as your engine is not overheating or losing coolant, and the radiator remains completely full to the neck, the upper hose collapse is not a major concern.  But, at least now you understand why.

[philo_beddoe]

The upper rad hose started collapsing after i installed the new heater core. The old core leaked. I will check that recovery for blockages and make sure the recovery hose is good.  Thanks

My rad cap seals well, the old one had no rebber seal, so vile gave me an oem one which seals good. Is my cap fine?

How much psi should the cap be?

[Irish_Alley]

my guess is the hose collapse due to air in the system. much like if you put a half open warm bottle of soda in the fridge once it cools the air will be denser than it was so it collapses. do you fill it while its running?

think generally speaking the psi should be 12-15

[philo_beddoe]

No, i filled while cold, engine not running. And yah, i looked up some oem caps, most were 15 psi. I'll check my cap and reservoir hose anyway. For the record, im not having any problems at all.  I just never seen a rad hose go flat as the engine cools.

Oh, and some of those true oem nos caps are like $40-200!!! I read the new ac delco rad caps are cheap made in india junk, with a paper gasket. How lame is that.

[zieg85]

Your cap sounds bad.  You should top it off while the engine is idling and at operating temp with the cap off through the entire time.  After that is done make sure the overflow reservoir is to the cold mark.  You should be good to go then with a good cap.  I never use anything more than a 12 psi with no AC.  My $.02.  My preference is Stant FWIW

[philo_beddoe]

I'll give it a go first thing in the morning. I'll change out caps and top off like you stated.

[Irish_Alley]

i wouldnt fill with engine at operating temp due to when you release the pressure via unscrewing the cap it will spray you. the purpose of a rad cap is to increase the temp before the water will boil. normally 50/50 will boil about 223° with each PSI of pressure the boiling point increases by more than 2°s so now that 223° boiling point is now around 255°and 260°. if the pressure builds up to over 15 psi the pressure release will open allowing the coolant into the overflow. since this just started happening once you changed the heater core i would think you have air trapped and this air condensing once the engine cools and the only part of the system that will give is the upper hose and i think im wrong on this. cause once the engine cools the cap should have a second relief valve that acts on vacuum and allow the coolant to refill the rad

[philo_beddoe]

Ok, this guy is saying the same thing.  "Vacuum"

https://www.yourmechanic.com/article/what-is-a-collapsed-hose

[zieg85]

i wouldnt fill with engine at operating temp due to when you release the pressure via unscrewing the cap it will spray you. the purpose of a rad cap is to increase the temp before the water will boil. normally 50/50 will boil about 223° with each PSI of pressure the boiling point increases by more than 2°s so now that 223° boiling point is now around 255°and 260°. if the pressure builds up to over 15 psi the pressure release will open allowing the coolant into the overflow. since this just started happening once you changed the heater core i would think you have air trapped and this air condensing once the engine cools and the only part of the system that will give is the upper hose and i think im wrong on this. cause once the engine cools the cap should have a second relief valve that acts on vacuum and allow the coolant to refill the rad

No taking the cap off when hot.  I said when cold take the cap off and let it heat up to normal operating temp, then top off.  All the air should come out and you should see a nice circulation of the coolant if it is a couple of inches low.  Top it off then put the cap back on.