Repainting a steel door

[Fisherguy]

We bought this house last year, it has 5 doors all with different keys!

Anyhow, I want to change the front entrance set and get 4 new deadbolts all keyed the same, no problem so far.

Problem is the front entry set has a big kind of backing plate, when I removed the old set I found the original owners masked it, so when I put the new set on I'll need to paint the whole door.
What is the process for painting a steel door with existing paint, how do I tell if it's oil or latex on there, and what will it look like applying the new paint with a brush? The existing paint looks like a good job, like maybe sprayed on.

Also, what can I use to fill old holes from the original set that will NOT be covered with the new set?
Thanks

[kactuskid]

First sand down the door and any edges that are high on the bare spots, then cover using an oil based primer. Then use an oil based rust proofing topcoat that's gloss or semi gloss. Here's a few things I learned painting my own steel door.

1. To take the door off it's hindges and laying it flat over sawhorses. This took gravity outta the picture which led to zero runs. Also took off the handle and the door sweep at the bottom so I could get good coverage on all of the door parts.

2. To slightly thin the paint down using mineral spirits. I poured about a cup and a half in the bottom of a roller tray, then added mineral spirits and stirred it up good. After thinning it about only 10% I used a 3" roller to apply the paint, then used a 2" natural bristle brush to smooth it out cause the roller left lots of bubbles. All strokes were in the same direction except for the inside edges of the panels.
(thinning it down helps it to self level which will give you a smoother look without brush strokes showing)

3. I sanded down all the flat area's using a 220 grit paper, vacuumed it off, then used a tack cloth to collect any dust that was left. Then applied a second coat using the same technique as above.

I can barely make out any brush marks as it self leveled nicely with the paint thinned down and it also gave me more working time to get it right. I sure learned a lot about painting using an oil based rustproofing paint on metal to get the kind of results I could live with.

[Distinctivescenes]

I agree with most of what the journeyman said. However, I use paint specifically for metal after priming. I also use a foam roller. I find it doesn't leave any marks behind. It eliminates a step, rolling then using a brush. You just roll once. I use this technique when I faux finish metal doors to make them look like woodgrains. Jan Distinctive Scenes