and now it's blowing white smoke on start up. Its a fair amount of smoke, but nothing like what it used to smoke like before the head gasket.

White/blue smoke on a cold start up is normal with any older mechanically controlled diesel. The main reasons are a lot of incomplete combustion and piston/rings to cylinder wall expansion rates being off compared to what they are when at operating temp. To minimize the cold startup smoke is the reason why these engines came with a cold fast idle and timing advance.

Would the low batteries impede the glow plugs from properly warming before starting, leading to the white smoke being unburnt diesel and maybe not coolant?

It stands to reason if batt voltage was good enough to crank and start, the glow plugs should have worked. However, if the glow plugs aren't working, the incomplete combustion (smoke) is way worse.

Could the sludge and oil in the coolant be from before the repair? Maybe just churned up during the first real long freeway drive?

Possibly, but another option would be that the O-rings in the oil cooler are shot and oil is leaking into the cooling system.

 

Hey guys,
I might have some input here, but back u would be appreciated as I am also new to the 7.3 IDI.
Firstly, Oil in the coolant can be normal after a coolant flush if the coolant was only flushed, I would say that you should flush it again and run some dish soap through it as the oil wont wanna come out with just water. It may take a few attempts with dish soap and water.
Secondly, you can get the O rings for the oil cooler for under $20 either online, at a local parts store, at an international dealership, or at a Ford dealership dependent on your region. I would reccommend also getting the cooler to block gaskets as you will have to take off at lead one oil cooler header to get the o rings changed. If you have any oil leaking from the front header of the oil cooler you will have a larger job on your hand (I have heard 3 hours), however if there is no oil leaking on the outside of the oil cooler you can cheat. All you will have to do is drain your motor oil, drain your coolant (Which should also be out as you will be doing a flush) pop the oil filter off, and remove the rear header (your oil filter mounts to this component). You should be able to pull the tube out of the front header while leaving the front header attached to the truck. I would refer to a thread specifically dedicated to this for more advice. This cheater method is not much talked about on the forums, because most people dont take the cheater way out, however this can save you about 2.5 hours potentially.
Thirdly, My 7.3 smokes like a son of a gun on startup no matter whether its hot or cold, give it a minute and it runs normal so dont worry too much about that.

Someone on here should let me know if the advice I have given is bad, because I believe it all to be good.

 

Sometimes those oil cooler headers are stuck, and require a little "friendly" persuasion to get them apart. So trying it while still on the truck might not be a very good idea. If you can get it apart that way, you still don't change the gasket on the front, and If I was going to do all of that work I would want to make it right.
Oil in the coolant; Dawn dish washing liquid works best. Use a heavy concentration fill the system, and let it soak for a good while. Drain it out, then rinse till it comes out without foam. Usually works the first time, but not always.

 

Someone on here should let me know if the advice I have given is bad, because I believe it all to be good.

Changing oil cooler O-rings without removing the cooler assembly is as impossible as replacing a crankshaft without removing the engine. Cleaning all the crud away from the O-ring areas so they might halfway seal would be a real joy, not to mention trying to press the assembly back together with part of it still hanging on the side of the block and other components in the way. I've never done a cooler on these particular engines but there comes a point where experience and common sense rears its ugly head.