C15 issues. Running hot, possible oil in coolant.

Hey guys, I need some help. Truck is a 06 387 with a c15.

A month ago I noticed it running hot, so I poked around and found the radiator was leaking, replaced that. Truck still ran a little warmer than usual. Last week I had an exhaust manifold gasket go out, and A AFTER they put everything back together they decided to tell me there was oil in the coolant. I fought with them over many issues (unauthorized work done, bill way over estimate..) I also brought up that if there were issues Roth the coolant I should have been notified right away. After some back and forth they said it's possible the coolant was contaminated after it was drained, they don't know.

My oil level has gone down slightly, and I haven't noticed any oil in the reserve coolant. Normal exhaust, no leaks, etc.

When running normal the truck runs between 180 and 190 like normal, oil temp is 200. When the truck has to work even on a little bunny hill the temps both climb, oil gets to 230 at most, coolant gets to almost red line but never there. The fan kicks on and pulls them both down quickly.

I've also noticed a drop in fuel mileage. Not sure if that's related.

Any ideas? I'm thinking oil cooler, but I don't know enough about these cats to say, maybe this is signs of another issue?

 

Check for what exactly? It was inspected when I did the radiator, and I've rechecked all hoses since to make sure they're tight. My boost pressure is still normal (45psi at max)

 

If the cac was leaking, wouldn't I notice a loss of boost? I can check it this weekend to be sure (I replaced the radiator myself with a mechanic's help)

 

Yes I do, and that has been normal. I've been close paying attention since the trucks been running warm to see if that would give me insight.

 

For the heat issue I'm going by both, the fan does kick on right around 215, it'll climb slightly higher and the fan brings it down, I'm now turning the fan on before a long climb and it keeps the temp down like it should.

As far as the oil issue I'm suspecting the oil cooler.