If you have coolant coming out of the exhaust it's a blown head gasket.

White smoke is excess, unburnt fuel. A leaky fuel injector can cause this. The tat-tat-tat sound is most likely an injector too. They can get as loud as a rod knock when headed south.

Since the fuel sat so long it may have algae. It can be treated with "Diesel Fuel Biocide" Here:
Power Service Products, diesel fuel additives, prevent gelling, clean injectors, disperse water, boost cetane, reduce emissions, improve fuel economy

Get a couple fuel filters as they will plug quickly when using a biocide.

 

I drive the truck home from work today and notice a small drop of diesel gaining, on the ground. Not a lot,but I'm thinking 'unburnt fuel is causing this white smoke, and I have an injector leaking'. So, I start to recall the glow plug work: I removed 4 torx screws and the injector cover thinking this is how I get to the glow plugs. I soon realized I did not need to remove this piece, and put it back on. Proceeded to glow plug work and am at this point now.
I'm thinking when I removed this cover and/or tightened it, the injector was not seated; or, the seals on the injector have blown. But, it does appear to be the one I removed (haven't removed valve covers to confirm, but I'm a betting man and it is on the side of the one removed).
In any event, I am going to pull that injector per the excellent instructions found at :

https://www.ford-trucks.com/forums/8...with-pics.html

After doing the glow plugs, harness, fuel pump, fuel bowl, I feel confident (especially with the above instructions) in removing all of the injectors and putting new O-rings on them. I'm no big mechanic, but thanks to this site and all your help and insight, I'm becoming a bigger wrencher. Keeps me out of trouble and makes me feel good too.

Again, I just want to thank you all for your patience and attention.

thanks,
mark

 

Keep us updated. I hope you find the problem and it is not too expensive.

 

Good luck, and I think you will be happy it is the injector. The mention of the coolant in the beginning brought all sorts of bad memories, something you definitely don't want to experience.