Hi I thought I should pass this along. I have a 1993 F350 that had been giving me starting problems. When I first started looking at why it was having problems starting, I started at the Glow plugs. The engine turned over but was cranking over several times and puff out smoke before running. Also the clicking of the glow plug controller was rather fast. Turns out that the half the glow plugs were dead. So fine I go and replaced ALL of them. Started better than before and I thought that was it.
Since this truck sits a lot I thought it was normal cranking a few times before starting. But then she started getting diesel smelly in the cab. So a few months after the glow plug replacement I see leaking injector fuel returns. It had gotten so bad the the cavity that the glow plug resides was full of fuel. So I got a rebuild kit and replaced all the return caps and lines. (But tip here - Moly lube 44) That stuff is great! It's a O ring lube that swells the O ring during assembly and keeps it sealed. Had I used it the first attempt. You only need a 2oz at most.
OK back to truck. So the leak repaired the truck started fine but a few months later I kept getting that clicking from the controller again. So I found a glow plug and controller set on ebay and gave it shot. Well that made a big differance. It really gets the cylinders hot and starts at the first crank.

Now it's summer here in GA and heat is all over. So I take the truck out to several places and my last stop, the engine would't crank over. Everything looks right. The glow plugs won't come on since it hot, very hot. So for the first time I have it towed home. Replaced both batterys since it's been over 6 years on them. Then put a charger on the truck and the next morning starts like a dream. I let it sit for a day and take it out again. And again when it's hot it won't start. I could hear the upper solinoid click but nothing happened. And it was dark enough to check if there was a load. Turned on the head lights and hit the key. The head lights did NOT dim. So a second time to be towed home. AAA paid for it's self by now! After going over all electical areas, I find that the plastic cap on the starter's solinoid was cracked and melted. It seems that all the time of having glow plug issues and return line issues as taken it's toll on the starter. When the engine was cold the contacts were close enought to arc and start the truck. But when it was hot, everything expanded enough to keep the contacts from touching. I got a replacment starter from Ebay (I even got the truck from ebay). Took only and hour to swap out. And what a differance. Spins over and starts faster than I ever seen.