You see it could be a combo of things, glowplugs faulty coupled with a wornout starter, equals overfuelled from attempted starts & hence smokey/misfires possibly, you need to get it on a diag tool to check glowplugs 1st of all, also as stated above can also check coolant senders whilst you're logged in as its not much bother, then check if they pan out, maybe chnage a starter over.
I have a starter if interested.