Two years ago replaced heater core, after market part. Recently had to again replace core becuase of leak. This time when the core was replaced I noticed that a glaze of oil covering the core and the box. I am not totally sure that it is engine oil, but it has me concerned.

I do go through a quart of oil every 1400 to 1600 miles and I had to top off coolant resevior but I think this was related to the core leak. The previous core did have a foam covering surrounding the core edges, could this be a result of a reaction between foam and antifreeze. The oil found does not smell or feel like engine oil.

Any thoughts.

 

the oily residue is probably antifreeze. its a greasy steamy mess.

 

Or, if the truck has A/C, it might be the evaporator core leaking, and that is oil from the A/C system.

Smell it. If it smells pretty sweet, it's coolant.

 

That was my first thought.

 

A/c definitely not leaking, although I guess I cold go with the antifreeze making a mess because its been leaking for several months.

 

As far as smell there is none.