Odd radiator behaviour!!

[Kennedy]

Thanks dom.....I get the same results from the cap supplied with new radiator as I do with cap from old radiator

I saw the post re combustion gas tester...might try the litmus test first

What is doing my head in is the fact that I released the pressure when it was cold and then it developed more pressure over 4-5 hours while just sitting in shed!!!

Checked overflow level this evening...it is still sitting at 12mm higher so doesn't seem to be sucking it back as it cools....BUT.....radiator is still full ????

[dom14]

Thanks dom.....I get the same results from the cap supplied with new radiator as I do with cap from old radiator

I saw the post re combustion gas tester...might try the litmus test first

What is doing my head in is the fact that I released the pressure when it was cold and then it developed more pressure over 4-5 hours while just sitting in shed!!!

Checked overflow level this evening...it is still sitting at 12mm higher so doesn't seem to be sucking it back as it cools....BUT.....radiator is still full ????

Yeah, the sucking back from overflow tank is not always perfect IMO, as it depends on the proper function of the radiator cap & outside temperature. Coolant system can develop tiny bit of cavitation inside the coolant passages due to water pump activity and uneven distribution of heat at the start up. Unless coolant blows out of cold radiator when you open the radiator cap, I don't think it's a critical issue. If you can confirm there's no combustion gas in that gas that blows out of the radiator, I probably wouldn't worry about it.
Also, definitely check the quality of the coolant, 'cos if the coolant is acidic for whatever the reason, it will most certainly produce gas inside the coolant passages by reacting with the metal. Some cavitation is ok IMO 'cos as you know, when the water boils there's always bubble forming out of water/coolant. It's the excess cavitation we need to worry about, 'cos that means either the head gasket/head is stuffed or coolant is bad.
Remember though, if you use the simple coke bottle gadget as I did to burp the coolant system or monitor excess cavitation/combustion gas leak, you need to plug the hose that goes from the radiator cap to the coolant overflow tank, otherwise coolant and air from the coolant system goes into the overflow tank and you won't be able to see whether there's anything wrong with it.

[Kennedy]

Thanks dom...I'll have a go at making the 'burper' when I get a chance and perhaps get it on a dyno next time I'm in the big smoke.

As I said earlier ...."What is doing my head in is the fact that I released the pressure when it was cold and then it developed more pressure over 4-5 hours while just sitting in shed!!!"

[dom14]

Thanks dom...I'll have a go at making the 'burper' when I get a chance and perhaps get it on a dyno next time I'm in the big smoke.

As I said earlier ...."What is doing my head in is the fact that I released the pressure when it was cold and then it developed more pressure over 4-5 hours while just sitting in shed!!!"

Yeah I can't explain that with a possible theory off the top of my head right now, but if you say it happens, then it needs some investigation.
I suspect some kinda coolant reaction with the metal inside the coolant galleries or it could simply be the air bubbles trapped deep inside the engine block gradually surfacing to the radiator top when it's cold. If there's no combustion gas in the coolant, I wouldn't worry about it.

I've seen some guys using a plain plastic bottle with the right size bottle neck shoved into the radiator cap hole to perfectly air tight it, without having to build the simple gadget as in my video. That might worth a try if you have few different size plastic bottles hanging around in the rubbish bins, etc.

[dom14]

Another thing you can check is to see whether you have any 90 degree joints(T joints) in the cooling system.
I've been told it's better to replace them with Y joints to reduce cavitation.

[dom14]

I've seen some guys using a plain plastic bottle with the right size bottle neck shoved into the radiator cap hole to perfectly air tight it, without having to build the simple gadget as in my video. That might worth a try if you have few different size plastic bottles hanging around in the rubbish bins, etc.

You can wrap the plastic bottle neck with stick tape or a piece of bicycle tube and then screw the bottle into the radiator cap hole.

[Kennedy]

Thanks dom, I will check it out

[Wizard52]

Do you have correct cap on overflow bottle as they are different.
When I installed new all alloy radiator, I did not notice the original cap was faulty in that rubber seal was folded under and did not seal. After noticing the fault, I swapped caps around and then coolant would not return from overflow bottle until I bought a new cap for radiator and returned overflow cap to correct place.
No problems since.
It is remarkable how the new radiator sucks the heat out and keeps temps down in recent 40+ temps even under load.

[threedogs]

Another thing you can check is to see whether you have any 90 degree joints(T joints) in the cooling system.
I've been told it's better to replace them with Y joints to reduce cavitation.

that is for gas systems mainly,