soot in the water.

[zipline mechanic]

im stuck.
we have a m35a3 with a cat 3116. ran fine then all the sudden theres not oil but soot coming out of the surge tank.we had the head checked replaced the gaskets and checked the oil cooler. all seems to be good. flushed out the cooling system ect...
still have soot like maga foam coming out the surge tank and it runs hot.
any ideals?

 

[cattlerepairman]

So it is pressurizing the coolant system with exhaust gas? If you have an emissions test facility nearby that is cooperative, they can take their exhaust gas probe and hold it over the opening of your expansion tank with your truck idling. If the probe sniffs out CO/NOx coming from your coolant expansion tank, then you have exhaust gas bubbling out of the coolant.
If you had the head checked and head gasket done, that leaves less pleasant possibilities, such as a hairline crack in the block...

I let others chime in; we have some really good CAT techs here on the site.