I have a 2003 Ford F350 7.3 diesel engine,Engine run fine,but only the problem diesel mix with coolant,what could be the problem.

Look on the bottle and see if it mixes with other coolants. If so.. Use it. If not, look to see what's in yours and see if it mix with it. If not. Drain you coolant. Add water, run it to temp, drain it again. Then add your good deal.

Get some BLUE DEVIL and follow the Directions. You have a Blown head Gasket or a Cracked Intake or Head.

Injector tubes are leaking.

Check the coolant temp sensor wire on engine for short.

all engines require motor oil

Have your injection pump checked. If the diesel fuel feed
going to the pistons is not highly atomized, there's no way that the diesel fuel gets to explode to keep your
engine to run. However, also check the air filter system
going to your engine. To get the diesel fuel to explode needs right air fuel ratio. Once these are checked, I'm
sure you get your diesel car running.

ford lists to use the ford gold premium, they advise not to use the orange extended life coolant for that year and motor, if you dont want to go to dealer then parts store should sell you the GO -5 FORD / DCX coolant. good luck.

IF it is a Head gasket leaking into a cylinder you wouldent see smoke you would see white steam coming out the exhaust tail pipe and you should get temp creeping up as the further you go and by wrights you should be getting a missing in that cylinder as you cannot {run on coolant but you can on diesel}, but if you find its the coolant getting either in through the seal under lip on liner or head gasket leaking in coolant but will get a lot worse before getting better as only needs a hair crack to cause your problem..

hello! judging by the key words in your statement, i assume your coolant has an oily type residue in it? very slimy?...tranmsisison oil coolers rarely fail on your type vehicle. it is more likely that your engine oil cooler has ruptured and has allowed the intermix of fluids. if that is not your concern, disregard and assume my ADHD has kicked into high gear!..by the way...your ford 6.0 diesel came with a manufacturers warranty on the engine of 5 years, 100,000 miles (with $100 deduct) if you are in these parameters...see your local Ford dealer!

you could have a blown head gasket, have a compression check done to see if there is any low cylinders,

a head gasket failure does not always allow water to get into the oil, the failure point can also be between the water jacket and the cylinder bore