Runs bad when it starts

Have you run a fault code test on this engine? If not do so.

run the fault codes to check for faulty sensors

have you looked into the injectors, or injector balance? glow plugs just preheat the cylinders before you start turning the engine over. if the injectors are dumping too much fuel it will run rich and blow black smoke, lean it will dump white smoke, same as if it has an internal coolant leak, but smell different. Ford has had problems with EGR systems on some of their diesels, being an older truck how many miles is on it? and the front fuel tank could have a bad fuel pump, pretty common for them to do what you have described. Also might want to have the timing looked at on it! It ignites off of pressure, and if the timing is off it will adversely affect the ignition of the fuel which will make for hard starts, and poor running. there is a lot that needs to be looked at to figure this one out! could be quite a few different things. Good luck!

It sounds like it has a bad main bearing, or it is dumping oil in the fuel (bad gaskets) You definitely do not want to run the engine with low oil pressure.

Take it to the pros they will be able to test and evaluate how bad it is .When you start blowing white smoke its a sure sign its hurt .

Blue smoke in the exhaust usually means oil is leaking into the compression cylinder and is burning with the air/fuel mixture. This would definitely cause hard starting.
As for how it's getting in there, that depends on how the car has been maintained. How many miles are on it.
First thing you should do is check your oil level. Make sure it's full. Keep track of your oil consumption for at least a week. Knowing how much you are using up can give you an indication how it's getting in there.

This could mean worn rings and cylinder walls or bad valve seals. It could also mean a crack in the block. This might shed some light on the cold air problem as well. Especially if your car overheated recently. Regardless what the cause is this is not a week end job. If your not comfortable with the thought of engine parts laying around find a good mechanic.
I really hope this helps and good luck.

The valve seals are bad, or its just worn out.

Ones the diesel engine gets weak its thn a hard start!, becausea diesel engine mainly fires up on good compression, i guess its time for an engine overhaul .

You need a belt and water pump. Hope everything works out for her. Good luck!!!

black smoke means not enough air to engine. and/or too much fuel. check intake system or bad map sensor. clogged air filter. good place to start