How does the Oil Cooler Work?
 

Long story short, brand new re manufactured block and heads after two minutes of running started to leak oil into the coolant, after pressure testing at the radiator it leaks out of the oil drain plug/pan.
The person who rebuilt the engine asked if i had an oil cooler and I don't.

Can the cap that is in there cause the oil to flow into the coolant?
Or do I have a bad engine?
It ran for about two minutes before we shut it off and didn't have time to warm up, never mind overheat.

A pro mechanic put it all together. Just wondering if he should double check that before we send the block back.

Could be as simple as a bad gasket could be a head or intake gasket.

Could be a cracked head or intake manifold.

Any place you have oil and coolant passages

Could have mixed a coolant and oil line :welder:

The oil cooler works just like a radiator, but uses the engine coolent instead of air.
It is possible (Not common since made of stainless material) that one of the water galleries has corroded through.
The seals going bad in the cooler would only cause a mess on the floor.

I would say bad headgasket.

Since I didn't have an oil cooler, is that just a plug to oil, or do both oil and coolant have a place where they might be blending??

It's just a plug. The coolant lines aren't in your oil pan. They're external on the engine for the oil cooler.

Sounds like your mechanic had trouble during assembly.

*If you have an oil cooler they're external.