Detroit 12.7 fuel in coolant

I had same problem but different engine,volvo d12.
My red coolant became almost water like clear,coolant tank got darker and there was some brownish build up on the inside wall of the tank.
I had to replace injector cups

 

I actually drove like that for 3 weeks. Truck was running fine,no problems whatsoever,no change in engine performance

 

That fuel will start to eat away at your rad hoses over time. Most likely culprit would be an injector seat. Suppose a cracked head could be possible too but not sure how close the fuel galley is to the coolant ports. You're definitely going to have to flush the system regardless. Personally I wouldn't run it.

 

I would drive it home,just keep checking it.

 

injector cup seals on mine. can drive for quite a while. but will get worse. mine pressurised the system so much that the reservoir cracked open.

 

I’d run it home. Not getting hung out at the mercy of thieves. The head needs to come off, to change injector cups. Very good chance, damage to cup(s) is minimal. New seal kits, ( o rings) are fairly cheap.A new graphite crush fire ring seals up minor damaged cups. along with a big fat o ring. Some claim it’s a bandaid, My bandaids held up for 3 yrs+. Otherwise if heads got to come off, might as well do an inframe.