Cooling system lesson (1 Viewer)

[Mongolman]

Can anyone give me a lesson on how the expantion tank in the cooling system is supposed to work. I have an RJ77 with a 22R engine and the other night when the engine had cooled down the top radiator hose was collapsed because of vacum in the system. I took the Rad cap off and it sucked in a bunch of air and went back to normal.

I know that when pressure builds up the spring in the cap is compressed and coolent flows through the overflow into the expantion tank. But how does it get back into the rad after the engine cools down? I am thinking that if there is negative pressure in the system it will keep the rad cap firmly sealed and not allow coolent back into the rad which explains what I saw. Is this correct or am I missing something?

Thanks
Marlow

 

[roscoFJ73]

Can anyone give me a lesson on how the expantion tank in the cooling system is supposed to work. I have an RJ77 with a 22R engine and the other night when the engine had cooled down the top radiator hose was collapsed because of vacum in the system. I took the Rad cap off and it sucked in a bunch of air and went back to normal.

I know that when pressure builds up the spring in the cap is compressed and coolent flows through the overflow into the expantion tank. But how does it get back into the rad after the engine cools down? I am thinking that if there is negative pressure in the system it will keep the rad cap firmly sealed and not allow coolant back into the rad which explains what I saw. Is this correct or am I missing something?

Thanks
Marlow

Hi Marlow .
I think the vacuum must pull the sprung seal down enough to suck the excess coolant back into the radiator.
In fact extra coolant should be added to the bottle when needed ,rather than the radiator. Thats why the coolant bottle has the high/low marks.
I check both of mine a couple of times a week and the coolant level is high when warm and lower when cooled so it must be going somewhere

Ive read that removing the radiator cap should only be done when necessary as it allows air in and disrupts the expansion and contraction cycle.
After you have removed the cap it will take a few days for the cycle to get back to normal

 

[David*BJ70]

Ive read that removing the radiator cap should only be done when necessary as it allows air in and disrupts the expansion and contraction cycle.
After you have removed the cap it will take a few days for the cycle to get back to normal

Mmmmm..... interesting.

Never thought about that...

 

[matt 105]

Gday.
Firstly, It should only take 1 cycle from cold to hot to cold to purge the over flow hose.
But to your problem, - have you changed the radiator cap recently?
In a recovery cap, in simple terms, the metal disk (about 5/8" 16mm across), in the center of the cap is the return valve. You should be able to pull this off the rubber seal with your finger nails - its a very week spring.
If your cap checks OK, make sure the overflow hose is not blocked.
Hope this helps

Matt

 

[Mongolman]

Yes I have just recently changed the cap. I will look closer at the cap and check the hose.

Thanks for the help

 

[matt 105]

well
what did you find?

 

[Mongolman]

I did not realize there was another valve that let the fluid back in as well as the main spring. I wanted a new cap because I had a small leak (just a dribble)from around the hard, old rubber washer on the old cap. When I bought the new one I ended up buying a cheap chinese knock off that did not have the return valve. I knew it wasn't OME because the metal was thinner but it did look good with the right color sticker on the top. This is typical of the parts we can get here because there are few places to buy from (I guess for $5 I should have known). There is a toyota dealer (I'm not sure if it is factory sponsered or not) but the parts there are incredibly expensive. So I went back to the original cap which I kept and will see if I can change the rubber gasket.

Thanks for the lesson