need some help from engine and boat guys

[plio7]

Ok here's the deal, I have a 1989 invader with a 3.7L engine with a closed cooling system (meaning I still run cooland with a heat exchanger)Couple weeks ago my oil went to milk....changed it and took it into a shop....shop calls says they ran it for 3 hours and can't find any signs of a leak, oil is still clean...this to the best of my knowledge is a very reputable shop that i have no reason to believe it BSing me .Any idea's

 

[Iron Horse Racing]

A few of questions....

Was the coolant level down?

Was the oil level high or just the wrong color?

Were you able to smell coolant in the oil?

Is it possible the motor was able to take in some water? ie oil filler cap off or loose, dipstick out of place....?

How did the motor run when you noticed this, ie working hard, over heated, over revved ?

 

[dtcat]

a relative had a problem with water coming into his engine ended up being a rusted through exhaust elbow this was on a 4.3

 

[TROLLCAT]

do you drain the lake water out of the manifolds and tthe heat xchanger every fall