I was replacing injectors on my dads 99 7.3l and one of the injectors had a grey sludge on it between the Orange oring and copper crush ring. The truck was running fine before hand, didn't have any signs of coolant in the oil, coolant levels never changed. Any ideas on what it might be?

 

It sure looks like it. Can you aim a camera and light in the hole?

 

That was the best I could do

 

I see green. Crack or bad seal, it's gotta come out. Check the injector cup link in my signature for a horror story, then you can use this to know where the land minds are.

 

Just did a pressure test and didn't see any bubbles. It's held the pressure for over 45 mins now

 

Coolant doesn't compress. When I did my cups and the coolant was drained, my pressure test showed bubbles with silicone spray. With coolant in there, you'll see coolant - but likely no air escaping. If there is a tiny leak into the cup, you won't see a measurable pressure loss in the system over a short period of time. Are you at 15 PSI? Is there any coolant at all going into the cup - even a few drops? If so, that's a bad seal or a crack - and it will not improve (self-seal) with time and miles.

While I'm not able to see clearly where the coolant came from, it appears to come from the top seal. This is a very bad place for a leak: It can send fuel to the coolant while the fuel pump is running, and coolant to the fuel rail when the truck is parked with a warm engine.

 

It was at 15psi, nothing showed up. My dad needs it this week to move things around town, will take back apart and see what we can find