It appears to be exhaust. Also getting some excess pressure in tanks and it is losing coolant. Haven't found any leaks yet. "99 F350 SD

 

Is it Oil or Fuel? That's the first thing that has to be determined.

A leak in the High Pressure Oil System causing oil to enter the cooling system. Or, a leak in the Fuel Deliver System causing Fuel to enter the Cooling System There are several area's to consider in diagnosing the exact culprit.

Bad O-Ring Injector
Injector Cup
Head Gasket
Cylinder Wall
Failure in the HPOP/Injector Delivery System

How long has this been occurring? Does it do it all the time? Or, just under a load? Have you noticed and performance issue or anything else out of the ordinary? Any information will go a long way in helping you determine where the leak is.

 

Oh crap. You're not going to like this answer.



That is usually caused by a combination of two issues: The injector cup may have a crack in it, and you have an injector not down tight enough to seal the combustion gasses from getting into the cup area - or maybe the copper washer lost it's seal. You could also have a cup that's split down the injector tip. Or... maybe the cup just lost its seal, but the cup is the only place that is a weak barrier between coolant and exhaust. Head gaskets rarely let go, but it is a very remote possibility.

It's not the end of the world, it's just a bit of work to replace injector cups. It's one of the less-expensive repairs to the truck if you use your own labor, but a shop will grab a bag of sand and bend you over.

 

Ok Tugly! The problem is like this but maybe worst. Is there some sort of test(ie, with AE) to narrow the problem. Thinking CCT?

 

There is a coolant combustion gas test kit at all auto parts stores. Around $20 if memory serves me. A handy thing to have around the shop.