Bobert -

Chances are the crack (and dent?) happened some time ago and may have been seeping oil for some time, or the crack might have been "closed" so there wasn't much leakage. If that's the case, you should find where the tractor "marked its territory" wherever it sat while it was waiting for you to get around to givin' it some work to do, although it may not be much of a mark. If it was a slit type crack, like usually happens when there's a dent, it's also possible that a good bump on the front of the oil pan flexed things enough to open up an existing crack at the rear end and turn a "seeper" into a "gusher."

Also remember that the poor machine didn't stop when the crack/leak happened. It only stopped when the oil pump stopped picking up oil and you lost pressure. That's probably at least a quart down below the add line. Usually the pickup is still good down to at least a quart or sometimes two below the add line, to give some safety margin. You don't want to run it that way on purpose, 'cause with low oil you're more likely to be suckin' up sludge from the bottom of the pan.

(An ex-spouse found that her little Toyota would run 3.4 quarts below the add line without the light coming on, and you had to change the filter to make it take 4 on a change. She repeated the experiment several times. But that wasn't the only reason we parted company.)

By coincidence, this afternoon I wheeled into a truck stop and saw a pair of feet stickin' out from under a fairly new Ford F250 supercab. The young lady who was watching the feet was sort of cute, so I strolled over to see what was going on, and she asked if I had a jack they could borrow.

He had a fairly hefty bottle jack, but he was trying to lift a five-foot long gas tank back into place to get the bolts into the support straps, and the tank appeared to be at least half full. Looked like one of the 'tween the rails 48 gallon jobs. One jack just wasn't enough to lift it and balance it into position.

I dug my scissors jack out of the storage compartment and let them have at it. I watched for a little bit to see if they knew what they wuz doin' (she was, like I said, sort of cute) but when she noticed I was watchin', even though I wasn't droolin' or nothin', she crawled down unner the truck with her guy where I couldn't see nothin' so I decided to leave 'em with their problem (and my jack). They finished it up pretty quick, returned the jack, and drove off, with him all covered with grease and the two kids smilin' and wavin' like it sorta happened every day.

I never did get an explanation of how a main gas tank falls off yer truck in the middle of an Interstate truck stop 70 miles from the nearest town with a population of more than 3; but I guess there's some mysteries we're not s'posed to unnerstand.

JB-Weld seems to be good stuff. It's the only available thing I could find a while back that's rated good above about 120F, except for silcones that have no useful strength. They rate JB good to 500F (260 C). Your crankcase shouldn't ever be running over about 375F, although some of the engine types say 395F is safe where the oil comes out of the block. Anything hotter will be breaking the oil down pretty quick.

My guess would be that the injury is an old one, and today you just flexed the wound enough to knock the scab off.

John