Small Engines (Lawn Mowers, etc.): Compressed Crankcase ?, oil drain plug, oil chamber

Question
I have a craftsman 20hp lawntractor with snow blower attachment. The engine is a Kohler CV624 5578. After running for about 5 minutes, the oil drain plug start to leak a lot of oil. I checked the oil level and it was within min/man. I let it cool for about 10 minutes, started it up and a ran it for a couple of minutes. When I removed the dipstick cap there was a fairly loud hissing noise.

Any ideas what might cause this ?

Thanks
MK  

Answer
Dear Mark,

I'd check these points first.
1> How hot did the oil temp seem after running for 5 minutes.
2.  Was the oil drain plug torqued to the maufacturer's specs.?
3. What was the colour of the engine oil? Did it look kind of burnt?

When was the last time an oil change [and new oil filter] was done?  
I'm unsure re: the hissing noise when you "opened the dipstick."
Where do you think this hissing came from?  It would be very unusual to have a build up of so much pressure in the oil chamber, but then you never know.

Hope this helps.

Howard

Engines run at very high temperatures.