help me on this one cooling issue

would seem that the oil cooler is not right yet. Probably would say it's a head issue, but since the oil cooler was last work done the odds kinda point in that direction.

 

Permission to thank and speak freely sir?
At a bit of a loose but I would associate the color with fuel in coolant, that should still seperate to top, or any mix coolant, it comes that color.
Would expect oil in radiator from the oil cooler since oil pressure is usually higher than coolant pressure.
In looking for cause of coolant in oil I wound start with trouble shooting flow chart. That is a Detroit 11.1 right? I thank it starts water pump, liner o-rings. Take the pan off and check those.
Never saw anything mentioned cause one the run hot also.
Air compressor has coolant, oil, and could put air in cooling system( equals over heating ).
The soot idea? With coolant in oil? Pin hole about 40% of the way down a liner?
Does the color of coolant in the jar go to normal with time?

 

Engine temp will vary,depending where your measuring water temp,its only an estimate,certain parts will be hotter than others.
Antifreeze and water mixture concentration,will change the temp.
Make sure you use distilled water when mixing antifreeze,dont use tap water.
As long as your below boil,and not losing coolant,dont worry about it.
Easy to contaminate cooling system,while doing engine work,if in doubt,flush the system,and start from scratch.

 

Oil floats.

So "black on bottom" can't be oil. Probably sludge that has been building in the coolant system for years and got loosened by the recent work.

 

You are correct about the water pump weep hole. Saw one stopped up once getting coolant in oil. I believe your engine also has 6 plastic plugs down the drivers side. The passages go to the middle of the liner o-rings. If the upper o-rings go bad coolant should leak out there instead of going to the pan. Cracked injector sleeve? A little fuel, a little compression in coolant?

 

My opinion,, i think he has a head gasket issue all along. Althou not a bad idea to change out a 22 year old oil cooler. But my money is on the head gasket .

 

Just a thought, but is there a chance that the coolant that was put in after the oil cooler was replaced was a different type? I know that the extended life red stuff does not play well with the green, and can plug up radiator cores. What has me wondering this is trying to come up with what the black gunk on the bottom is that could be heavier than coolant.