B7100 Leaking Coolant From Overflow

[Hdoilcan]

I have a B7100 hst that this past summer kept leaking the anti freeze coolant from the overflow. I壇 fill it back up and mow approximately 1 acre and it would loose about 20 oz. it just leaks from the overflow. Any idea why this would be happening?

 

[Thomas]

Some B7100HST radiator caps would make whistle noise if over heating...has yours.
Maybe the radiator cap needs to be replace or radiator fins are plug need good washing,also check radiator hose.

 

[J H Musser]

Just for comparison, I have a B 1700 purchased new in 1996 and after about 10 years the radiator core just couldn't cool as well. The engine temperature would heat up and then I would get the overflow you discussed. No matter how much hosing off or using compressed air I just couldn't get the radiator to work as good as when newer. Solution was to replace the radiator core. Easy fix and problem went away. Running the engine at high temp will cause unwanted problems and annoyance. Also a good time to consider replacing the radiator hoses. Hope this steers you to a solution. Good luck.

 

[ericm979]

The one time my B7100HST did that it was because the radiator and radiator screen needed cleaning. The whistle is on the overflow, it's telling you that the radiator is boiling over.
If it still happens with the radiator and screen clean so the air flow is not blocked, then there's a cooling system problem or a bad head gasket.

 

[sandyc]

Head gasket ?

 

[Coyote machine]

Depends on several things. How old is tractor, # hours on it - have you ever changed out the coolant since new?
Could be radiator/screen debris, rad core/low flow, head gasket defect allowing gases of combustion to blow by into coolant, thus overheating. Also defective rad cap/T-stat, etc. Give us more details about tractor, primary uses, stored in or outside etc.

 

[Hdoilcan]

The tractor is a 1993 with just over 800 hrs. The previous owner only used it to mow the lawn and that’s all I use it for. When I purchased it two yrs ago I changed all the fluids. I put approximately 40 hrs on it myself. The previous owners stored it in a garage. I store it in a run in type of barn.
As far as I remember there’s no debris blocking the radiator or anything like that. I’ll double check tomorrow to make sure.

 

[Gator6x4]

Head gasket ?

Yes internal combustion engines have head gaskets.

 

[Coyote machine]

With the age of the machine and # of hours on the clock, and seasonal use vs, everyday use, it's entirely possible that something has dried out, like a head gasket, radiator cap seal, etc.
I'd start by checking the obvious things; clogged screen and or radiator fins clogged. I don't know your specific tractor model, but it should have a fan belt and water pump. Check under the water pump to see if there is any evidence of coolant leaking out the weep hole and down the front of the engine. If there is a leak, it will usually be evident by being cleaner than the rest of the engine. Also check the fan belt for cracks, glazing of the contact sides, and tightness; 1/4 to 1/2" deflection between the top of the water pump and the alternator is sufficient.

Next, open the radiator cap, NOT the overflow tank cap, (assuming there is a cap on the actual radiator), and start the machine and let it run. What you're looking for is flow of coolant past the radiator neck, withOUT the coolant rising to the point of overflowing out the radiator's neck/opening. Let it run for some time and see what is happening at the neck. Do you see fairly rapid flow of coolant by the neck or is it not flowing at all, or very slowly. Over time does the coolant level rise and eventually overflow at the neck along with excessive bubbling of the coolant?
If there is low flow even with a helper slowly increasing the rpm's of the engine once it's reached near operating temp, one could suspect a faulty thermostat, or clogged or worn out radiator core. If you're seeing bubbling of coolant and overflow at the filler neck more likely a head gasket failure. If low to no flow of coolant, a water pump or clogged radiator.

Again based on age, a poorly functioning radiator could be a likely cause. Before doing anything else, report back your findings, and any questions.

As we move forward, you can if indicated, take your radiator to be checked and either flushed or recore it IF you have an all metal radiator. If it has plastic headers, it's toast- it cannot be repaired/recored.
Post back results....

 

[ericm979]

The B7100 uses a thermo siphon cooling system. There is no pump or thermostat. Hot water in the engine rises and moves into the radiator where it cools and sinks and goes back into the engine. This kind of system needs large hoses and big coolant passages.

A bad head gasket is the most likely culprit but there's other possibilities like a partially clogged radiator or hose. Does the fan turn like it should? Is the coolant in good condition and what Kubota recommend? If yours has the radiator screen (p/n 66204-51450) , is it clean? I periodially had to remove mine and use a brush to clean the dirt out of the small holes.