2006 VNL630 D12D problems

'06 D12D 435 HP, 1.2 million miles, rear main seal leaks a little, engine does have blow by. The truck has always ran good and always started up right away no matter how cold. On my last load, I parked the truck as usual. Then on the next afternoon went to start it, it cranked over but never started. I noticed coolant was down below the minimum mark, and oil level was down 1.5 gallons from the day before. So I'm thinking these low fluid levels had put the engine in a "no start" mode. So I top off the fluids, disconnected the preheater, and gave it a few shots of either and it finally started with a lot of stumbling and white smoke with the smell of unburned fuel. After it warmed up, it ran fine as usual, though I did not drive it. I then change the fuel filters, and it started without any problems. So the next day I went to start it to go drop a trailer, and again it would not start. I finally kept cranking it over till it finally started with the stumbling and the fuel laden white smoke. I notice that coolant level was down to the minimum level again but no sign of where it went.
Can someone help me understand what's going on here. I have not driven it since the problem started. I didn't want to leave with a load and may have to be towed. Can someone offer ideas. Thanks

 

Thanks for the reply. Well I went today to see what it would do today. I would not start. I had to spray it again. But before I started it, I check the oil and coolant. Oil was full but the coolant reservoir was nearly empty. I drove it a few miles and it ran good. The other day when I change the filters, I let the spin on fuel filter drain into a bucket. I check it today and there was about a half pint of antifreeze in the container. So is my coolant getting into the fuel? How is this possible?

 

Yes it does have a Davco. When I drained to to change the filter, there was only about 2oz of water in the bottom... no antifreeze.

 

The antifreeze was in the spin on filter.