pressure relief or faulty drain plug?

[bfoote]

I have an Allis Chalmers 5050, and was working it yesterday moving blocks of firewood. I loaded a lot of blocks into the bucket, and the tractor was working a bit, but I only moved three loads, and then called it quits. When I was going to park the tractor, I noticed a steady stream of antifreeze coming out of the drain plug on the lower radiator hose. Its a drain plug, and it has a nut which bolts it on the lower radiator arm. I quickly looked at my temp guage before shutting off the tractor, and it was not showing the tractor running hot? I shut off the tractor, and the antifreeze was starting to slow down coming out of the drain plug, so I thought that removing the radiator cap would take the remaining pressure away, but when I removed the cap, the stream started coming out full stream again. I replaced the cap, the fluid stopped coming after a minute or so, maybe a half gallon came out. Now I'm questioning whether this is a faulty plug, or is there a pressure relief valve built into this? Thanks in advance...

 

[BeeferMan]

If it leaked worse whe you loosened the cap, then I'd have to say it's a leak as that's when there would be *no* pressure in the system.

Now the leak could be due to a bad pressure relief valve, but I've never seen a pressure relief valve on a cooling system (other than the cap itself), and anyway, a pressure relief should *not* be on the bottom of the system (where it would bleed fluid), it should at the *top* (where it would bleed air)

Long story short - sounds like you have a bad plug...