As it is a used vehicle, my husband is not sure of all the mods done to it, but knows that some were done.
Should he chance coming back to Iowa without having it looked at first or does he risk messing the engine up?
Just a thought, but has he checked to see if he is losing transmission fluid? The white smoke might be the fluid leaking on to his exhaust.
cycle the key 3 times leave it on (no start)and watch the odometer see if its showing a code?
Assuming head gasket is ok.
Stuck injectors can cause white smoke in 6BTs. Exhaust will smell really heavy of diesel fuel. Failed thermostats (stuck open) can also cause this condition...but I have only seen this in cold weather.
Verify that you are not burning oil...which is a blue/white smoke. Burning a lot of oil in diesels is a safety issue.
It's a MANUAL transmission, so it's not likely that it's leaking transmission fluid on the exhaust. Possible, just not likely.
It's also a FORD with a CUMMINS 6BT swap, so there would be no check engine light or any codes to check
If it's smoking, it's either consuming (burning) fluid or leaking fluid onto something hot and combusting it externally.
Fluids that could produce white smoke could be:
Power steering fluid
Engine oil
Coolant
Transmission oil
The turbo has both a supply of coolant and engine oil. If the turbo suffered a failure, like a blown line or seal, either could be entering the exhaust and coming out as white smoke. Or leaking externally on those hot components and burning off externally. Since this is a van, this would be happening right under the engine doghouse and he could probably smell it right there in the van. He could/should pop open the doghouse and check for any signs of upper leaks.
A failed head gasket or cracked head could be introducing coolant into the combustion chamber and burning off as white smoke. This would be truly white, not blue-ish white, and would smell sweet. This would also be the case if coolant were getting by the turbo, either upstream or downstream of the engine.
A failed injector introducing raw fuel into the combustion chamber at a rate that could not ignite would produce white smoke but it would be acrid and smell heavily of (what else) diesel fuel. You'd smell it only at the tailpipe. It would quickly wash down the cylinder walls and dilute the oil, potentially ruining the lubricating properties of the oil and causing catastrophic bearing damage. Check oil often, not just the oil level (it would show a high level) but smell and consistency.
Oil anywhere inside the system (turbo up/down stream, internal oil leak) would produce blue-ish white smoke that was thick and heavy coming out the tailpipe. A failed turbo oil seal on the cold side (inlet) can cause a runaway condition where the "fuel" becomes the leaking motor oil itself so it cannot be stopped with the throttle or ignition switch.
An external leak would burn that oil off anything hot, and you'd smell it (and see it) at/near the source. Same with power steering fluid or transmission oil. If he doesn't see any leaks, see any smoke outside the motor, or smell any smoke except for the tailpipe, it's not an external leak.
Whether he should press on until Iowa depends on his mechanical aptitude to determine which of these things might be happening. Get it wrong and it could be expensive. If he chooses to press on, keep an eye on all gauges and fluid levels and stay away from long periods of full throttle or high boost.
Good luck
