When I removed the oil pan of my ‘78 L82 to replace the rear main seal, I discovered the coolant was leaking internally into the oil pan (see picture). I suspect intake gasket but would like other opinions. I obviously need to fix this problem. 

I don't see anything in that pic that indicates coolant in the oil....might just be my old fart eyeholes. I also do not see any indication that that engine has been run with any coolant in the oil. That being said, if you see coolant, it had to come from somewhere. Has this engine been sitting for some time without being run? If so, then it is possible the intake gasket(s) are leaking at the rear, and coolant is seeping down into the oil pan.

Joel Adams
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While the coolant crossover in the intake manifold gasket is usually what contributes to coolant in the oil. Mine happened to be different in that it had several micro cracks a fraction of an inch long between the three and five lifters in the block.

One way to check for coolant in the oil is to look at the underside of the fill cap. If it has a emulsified or jelly like substance on it then that was probably because of coolant in the oil that is condensing out on the backside of the cap.

1973 L-82 4 spd

Thanks for the quick reply and input. Since this engine has all the correct numbers for my 78 Pace Car I hope it is not cracks in the block. Either way I will need to pull the intake to do an inspection. How did you resolve your issue?
Jon

Boynton Beach FL

Joel, thanks for your valuable input. Here are a few more details. 
I have had the car for about a year and drive it on short Sunday afternoon rides frequently. I check the level of the coolant frequently (By taking off the radiator cap) and it has always been full. Before I pulled the pan I drained the oil that was in the car when I purchased it. It was dirty indicating it had been in there for a while but no sign of excessive coolant. Although, their was a very small amount of fluid that was not oil (about a tee spoon).

if you look closely at the picture there are two green drops of fluid. One coming off the bearing cap bolt and one coming off the rear flat surface of the block. Although not in the picture there was a drop of coolant out of the hole the oil pump shaft goes into. That is where the fluid leaking off the bolt came from. 
Jon

Boynton Beach FL

My machinist had three ways that he said could be used to repair the very tiny cracks. One was to drill a hole at the end of one of the cracks & tapping for a small plug and epoxy it in and then move over about three quarters of the diameter of the plug and drill and tap another hole and epoxy on another plug. Continue this process to the end of the crack.

The second method was to weld it. Welding cast iron can be problematic.

The third method which I opted for was to V the crack and repair it with J-B Weld.  Don't forget that these cracks in my block were microscopic and were not really visible without pressurizing the block and spraying with something like simple green and look for the bubbles. I don't remember exactly but the cracks were probably less than a 1/4 inch long and there was only two or three of them.

1973 L-82 4 spd