radiator and over flow question

[Stocker]

Originally Posted by purple gas

so, does that mean when the prerasure valve in the cap closes, and the "coolant" cools down there is a negative preasure, or in essence a vacume within the system?

Yup - so depending on how you visualize it, either the vacuum within the system sucks the coolant out of the overflow tank, or - when atmospheric pressure exceeds the pressure within the system, it (atmospheric pressure) pushes the coolant back into the radiator. Same difference.

[68LSS1]

Originally Posted by Stocker

Yup - so depending on how you visualize it, either the vacuum within the system sucks the coolant out of the overflow tank, or - when atmospheric pressure exceeds the pressure within the system, it (atmospheric pressure) pushes the coolant back into the radiator. Same difference.

Not the same difference. Atmospheric pressure has nothing to do with it. As a liquid is heated it expands which creates pressure. We release the pressure via the cap to the tank. There is a seperate part of the cap with a return or check valve that is held closed by this pressure. As the system cools it shrinks which creates a vacuum which draws fluid from the tank. I am not following you logic about what atmospheric pressure has to do with it. When you put a tire pressure gauge on a empty tire what does it read? Zero, no pressure. With your line of reasoning I would have 14.7 psi in the tire. Explain to me how atmospheric pressure has something to do with this, I could be wrong, have been before (once in this thread already ) and will be again.

[Goffer]

If I go with the 'Be Cool' recirculating catch can through Jeg's how are the lines hooked up?

[Stocker]

Originally Posted by 68LSS1

Explain to me how atmospheric pressure has something to do with this

It's simply the difference in pressures. Ignoring the cap for a moment, greater pressure in the radiator = coolant flow to the tank. Inversely, greater pressure in the tank (yes, from atmospheric pressure, which is greater at sea level than at high elevations) = coolant flow to the radiator. If the vacuum explanation works better for you, go with that. As to your tire pressure analogy, the gauge reads the pressure relative to atmospheric pressure.

[Southpa]

Heres an overflow bottle I installed years ago when I learned that the lower 1/4 of my rad was plugged. I didn't have the time (or the funds) to replace the rad til later. Temp was going as high as 260 deg. and she was puking massive amounts of coolant. OUCH! But that sure says something about the original 1970 350 in my truck, shes still holding her own!

Anyway, the bottle is from a 1982 camaro, it mounted nicely on the inner fender with 2 screws. See where the tube goes into the top of the bottle? That tube continues (as part of the bottle) down to the bottom. If you find that your coolant level in the rad is down a little every time you check then your system is not totally enclosed. Air is less dense than coolant so every time your engine cools down (and coolant volume contracts) you are sucking air back into the system. The cap on the bottle has to be vented or the bottle will get crushed when the coolant contracts (negative pressure in the bottle is less that atmos. pressure) and/or explode when the coolant expands (positive pressure in the bottle exceeds atmos. pressure).

Check under the truck for any signs of coolant dripping when you shut down after driving. Thats when temp and pressure is at its highest. If you do find a leak don't attempt to fix it until everything cools down. I've stripped hose clamps before and its not a pleasant experience when a hose pops off. Its messy and extremely dangerous. Check all your hose clamps/connections, make sure they are tight. And check the hose connection to your coolant bottle, look for cracks, pinholes etc. in the bottle.

Thats about all there is to it! An enclosed system that operates by the expansion and contraction of coolant.

[chickenwing]

Originally Posted by 68LSS1

... I am not following you logic about what atmospheric pressure has to do with it. When you put a tire pressure gauge on a empty tire what does it read? Zero, no pressure. With your line of reasoning I would have 14.7 psi in the tire. Explain to me how atmospheric pressure has something to do with this, I could be wrong, have been before (once in this thread already ) and will be again.

Actually there is 14.7psi in the tire. Everone drops of the G that should be at the end of PSI. G stands for gauge. A regular tire pressure gauge starts at 0 accounting for atmospheric pressure allready present. As far as the rest of the post... I still ain't figured it. There really is a check valve in a radiator cap?

68LSS1, I also think your tire pressure would increase with altitude. You fill a balloon at sea level it's x psi plus atmospheric. You go up in elevation the balloon is still x psi plus atmospheric where it was filled. The balloon will expand. In your above example the tire pressure would be 39.5 psig at altitude. Assuming calibrated/accurate gauges.