Have an ex-military tractor, hours unknown, serial number unknown, 

the tractor is living its best life on my farm last 3 years.  Had not checked coolant level in a while,  was moving the dozer back to the barn after using it for a Christmas display with Santa  out by the road. Noticed the engine temp going above normal.

added almost 5 gallons of coolant to top it off , left the cap off and ran the engine
getting bubbles coming out and have a mix of oil as well

No sign of increased oil level in the engine , have not tested or tried to drain the oil yet to check for water there.

with cap on the amount of pressure in the coolant system in low enough it not cause the pressure relief valve to discharge.

Of course I have gone to my dark place suspecting a blown head gasket. 

The engine fires right up and runs with good power 
The exhaust appears normal to me ,  that being mostly not visible unless loading it up.
It does use some oil, and has some blow by,   Engine compartment is dry , To me not bad for a 50 year old girl.

looking for ideas to check it out .