Cold weather operations

[flyined]

My partner on Long Island, NY put our J-3 on skis and went for a flight in very cold weather yesterday. He told me that after his hour long flight while taxying in, the engine stopped. Oil was seen coming out around the filler cap and the tach drive cable. When he got the plane into our heated hangar a 7" cylinder of ice slid out of the breather tube. Apparently pressure built up enough to cause the oil leakage.
Can any of you cold weather flyers tell us how to prevent this from happening again?

 

[cubdriver2]

 

[J3 Driver]

 

[soyAnarchisto]