Thermosiphon system question

[procraftmike]

I added a coolant recovery bottle to my B7100 last summer, thinking that it would work like a conventional cooling system, where coolant would be drawn back into the radiator during cool down. That does not seem to be the case.

The radiator will shed some coolant into the reserve tank, but it does not seem to draw it back, during cool down. I checked the cap and it does have a vacuum valve on it, so I am thinking it should work.

Has anyone else added a recovery bottle to this type of system and had the same results? Anyone have any ideas why the system does not draw back the coolant during cool down? I have no coolant leaks anywhere. The radiator was cleaned and pressure checked last summer. All new radiator hoses as well.

Thanks!!

 

[85Hokie]

Mike,

I do not have the overflow bottle - but I will tell you this, IF you fill it too much, it will spit it out!

The first couple of times when I ran my 7100 - it would drip and slobber out some fluid, I kept placing it back in. After I while I realized that it wanted to be at a certain level - period. That level is roughly the top of the top "fin" - which is a good inch below the neck top, might be closer to 1 1/2"!!

As for the suction NOT drawing fluid back - does the tube run all the way to the bottom of the container? AND if so - it would have to suck a good deal of fluid BACK into the radiator for anything to be noticed - once cool, what is left in the hose would drip back into the container - especially if the container is lower than the radiator top.

 

[dandeman]

I've added overflow reservoirs on several long ago past cars.

The radiator cap needs two seals for this to work, one being the spring loaded rubber that seals the radiator to pressurize the system; which actually, it's the round metal disc in the center of that rubber that serves as a vacuum relief valve that allows air (or water from the overflow tube in a container of water) to come back in the cooling system as the engine cools down.

The other seal that needs to make is the "upper seal" in the cap (shown in the photo) sealing to the radiator neck and of course no air leaks anywhere in the upper part of the cooling system.

Also the large radiator hoses need to be rigid enough to not be collapsing when the slight vacuum is formed as the engine cools down. I've seen a number of engines use hoses on the intake side of the water pump that have a metal spring or other reinforcement to keep the suction of the water pump from collapsing the hose.. Some engines use these on all the large hoses in the cooling system. Look for a collapsed hose when it cools down.

 

[procraftmike]

Thanks Guys!!

Hokie, It does spit coolant out the tube if I fill it too much, but I would expect it to draw it back in, once it starts cooling down. Maybe with this system, it expels more coolant than a normal system and thus, is not able to draw it all back in. I have looked in the radiator after it cools and the coolant level is still above the top fin.

My coolant bottle is slightly lower than the top of the radiator. The hose comes out the bottom of the bottle. It's not possible to get the coolant bottle above the radiator and still keep it under the hood.

Dande, good information on the hose spring. I replaced the upper and lower hoses, so I know there is no spring in them to hold the shape. I am sure it doesn't take much of a change in hose diameter to make the system not pull all the coolant back. Maybe I will get a new radiator cap, since I do not know how old the one is that came with the tractor.

Thanks!!

 

[MikeyA]

There should have been a little "whistle" on the end of "overflow hose". That was the indicator when motor was getting too hot, it whistled!! All you had to do was stop, idle down for a minute or two, and it would cool off enough to continue working.
You would need a radiator cap that was meant for a surge tank application to work that way, but that defeats the warning system that B7100's use...at least that is how it worked on my 1994 B7100HST.