Radiator Cap Question B7100

[ant126]

I have an old style Kubota B7100 HST. So I had been doing some brush hogging on a warm day recently for about an hour and a half when I saw a small amount of stream come out of the radiator overflow tube. I turned off the pto and drove the tractor for a minute and turned it off to let it cool down. I haven't done a lot of work in the heat with this tractor until now, but I keep the radiator pretty clean and that day was no exception radiator was fairly clean when it got warm. I checked coolant level after it cooled and it was maybe 1 cup low. I am guessing some steam had escaped before I had noticed it. No coolant leaks anywhere else on radiator, hoses, etc.

I read some posts on here and did some digging and didn't know how important the differences in radiator caps was. I have my parts manual so I checked and from what I can find using the parts number mine is supposed to be a 13 lb cap. I went back to my radiator cap and luckily the numbers had not completely worn off like almost everything else had, it clearly says 7lbs! I don't know for a fact that the radiator is original, but even if it is a replacement isn't it likely it would need a cap rated for higher pressure than 7lbs? Either way I ordered a 13 lb cap to give it a try. Is there any reason someone would purposefully put a lower pressure radiator cap on this tractor?

 

[ant126]

Update: In case it helps anyone else I found no reason someone would put a lower pressure cap on a system that works well and can handle higher pressure. I put the right radiator cap on the B7100 and used it for a few hours the other day works great, no leaks, no problems. I even used a laser thermometer multiple times on radiator hoses and found no temperatures out of the normal operating range.

 

[Dave_eng]

Does your rad have a working whistle?

Remember, there is no water pump. Thermosyphon system

Dave

 

[ant126]

Dave;

Yes, thanks I know it is a thermosiphon system. It does not have a whistle, I am sure it did at some point but it doesn't anymore. I like the B7100 a lot, it's a great little machine, but I am coming around to seeing that given the largeish acreage I am trying to manage I am going to put it on the market soon for something larger. I have a 4ft bushhog I mow with, but it takes so long going relatively slow to mow 20 acres with a 4ft bushhog it is just tough to stay ahead of it.

 

[dewders24]

The reason anyone would install a 6-7# radiator cap vs the typical 13-15# radiator cap would be to put less stress on a perhaps weakened or old and neglected radiator. The benefit of the few pounds of pressure is merely raising the boiling point by a few degrees. It does no harm to run a lower pressure, in fact if you would happen to spring a small leak, the lower system pressure will let you hang on to more coolant for a longer period of time. Also, the lower pressure puts less stress on water pumps, hoses, and gaskets in general...no matter what type of vehicle.