Thermo Syphon Cooling Question

[SteveM]

Since you folks are the pros at vintage compacts, I posted this here -

I have a 78 Kubota B6000E with thermo syphon cooling. Last night while mowing in cool temperatures, steam began blowing out the overflow valve. After a quick idle and shutdown, steam blew at high pressure for 2 minutes. After some time to cool, I inspected the radiator (no leaks, fan belt fine) and refilled with water. Tractor started and ran fine for 5 mins to get it back in the barn.

1) Could this have been caused by a low water level in the radiator? (havent checked level in a while)
2) What is the proper water/antifreeze mix for upstate ny winter use?

Thanks for your help!

 

[gbirky]

SteveM,
It could be that your water level was low. Did you make sure that air flow through the radiator was not blocked? Sometimes during heavy mowing - especially in dry weather, a layer of dust, dirt, grass clippings, etc. can build up on the radiator causing the tractor to overheat. It could also be that it is time to run some radiator/coolant system flush to get the inside of the radiator nice and clean. Other possible causes of overheating are a bad head gasket, or cracked head - but I'd try cleaning up the system good and running just water right now to see how that does.

As for antifreeze mix - that would depend on what temperature you want to protect it to. In very cold climates, I would run just water in the summer, and then put the required antifreeze/water mix in for the winter. The cooling system doesn't function with a mix of more than 40% antifreeze.

 

[Ozarker]

You didn't say if your temp warning light came on. If it didn't, and if it works properly, the problem could have been the radiator cap. Mine has to maintain 13psi (I think) of pressure and if the spring got weak it would boil over even tho the coolant wasn't really overheating.

Water boils at 210F at sea level. The higher you go, the lower the temperature at which water boils. That is why you have to boil water longer on high mountains to purify it than at sea level. because it is boiling at a lower temperature.

Conversely, putting water under higher pressure allows it to go to a higher temp before it begins to boil. That is why you never open a radiator that is hot. Water that isn't boiling will immediately begin to boil when the pressure is released if it is above the boiling temp for your elevation.

All that said........a bad radiator cap will make a radiator boil over even if it is not above operating temperature.

 

[roger_scotty]

Steve, those old thermosiphon systems need to be kept clean and full. What you describe sounds pretty standard and generally no harm is done if you shut it down while there is any coolant at all left in the system.
Yes, if the coolant gets below the level of the upper radiator hose then the tractor will overheat everytime. As you know, there isn't a pump to push the water into the radiator....so thermosiphon requires a continuous fluid path through the engine and radiator.
To make it run like new, here is what I do: Use a garden hose to backwash the outside of the radiator fins from the fan side, then uncrud the inside with a weak (about 25% strength) mixture of Prestone radiator flushing chemical. Run the motor with that flush in there just until the temperature comes up - maybe 10 minutes - and then shut it down, drain and repeatedly flush the system with clean water. A garden hose in the filler spout works with the draincock open works good for that.
Look at the radiator cap. If there is any doubt about it being the right one or if the lower gasket is shot, replace it with a STOCK OEM cap if you can get it. Otherwise a 14 psi type....give or take a psi. It has to seal well on the inner surface of the radiator neck. Most caps are the type where a spring pushes a rubber gasket down to make that seal an inch or two below the level of the cap. The spring itself is what unloads at the rated psi and lets the steam out the overflow. The upper seal right under the cap itself is less critical. Some caps don't even have a seal there.
Refill with about a 50/50 water/antifreeze mix. Thats what I use here in the Colorado mountains and is OK for summer and winter both. Best practice is to premix it and shake it up before you pour it in.

 

[SteveM]

Thanks! Re: Thermo Syphon Cooling Question

I cant say how much I appreciate all this help! I filled the radiator to the proper level with 100% water last night and ran with no incident for about 30 mins, so I do believe it was a coolant level problem. (how dumb can I be..) anyhow, I will now spend the forecasted rainy weekend happily flushing the radiator, which I had been wanting to do before winter anyways - thanks for the great instructions!

If I ever find a clean Yannie with loader in upstate NY, I will buy it and become a true member of this forum