OK, here’s the story.

About a month ago, I noticed that my 1990 Honda Civic DX (with
automatic transmission and A/C and ~75,000 miles) started getting hot
within 5 minutes after starting out. Almost to the red line on the
gauge. I was stuck in traffic when I noticed this. I immediately tried
to pull off a freeway exit. As soon as I got off the exit, I noticed
the temperature drop almost instantly on the gauge from the line below
the red to midway on the gauge. But then a couple of minutes later
through town, the temp went back up again, only to drop back down
later when going back onto the freeway. It did this on the remainder
of my freeway trip and ever since then. Doesn’t matter when or
where I start out (morning/noon/night, freeway/town), this pattern is
consistent. It continues this same pattern: a couple of minutes after
starting it would go to almost the red line on the gauge, a couple of
minutes later back down to midway on the temp gauge, back up to almost
the red line, back down, etc. etc. etc. Never overheated to where
steam was pillowing through the hood. As it happened during the
Christmas holiday season, I passed it off for fixing until after the
holidays, driving it all the while. I would put on the A/C just to
keep the fan blowing on the radiator.

I did a little research and concluded (rightly or wrongly) that my
thermostat was stuck. So I went to Honda last week to get a
thermostat. However, as soon as I was about to replace it, I saw the
cooling fins on my radiator were bad. They were disintegrating,
crumbling. Whether the thermostat is the root of the problem or not,
the radiator will most definitely need to be replaced (I intend to
keep the car for at least a couple of years). So I decided that I will
go ahead and have the radiator replaced.

My questions to you folk:

Do you think that the radiator is the root of the problem with the
symptoms I am having? Initially, I was hesitant to think the radiator
was the problem because if the radiator was that bad, wouldn’t
it lead to the car always running hot (i.e., not cool and hot like
it's running now)?

OK, more importantly, I am thinking that I will attempt to replace the
radiator myself and have some questions regarding this. I normally
would send the car to Honda, but right now I am trying to pinch
pennies as I just bought a new home and have a new child in the
family. BTW, I am not a mechanic, but I consider myself fairly handy
as I do regular maintenance on the car (tune-ups, oil changes, etc.)
and have done slightly more significant repairs to my previous car, a
’83 Honda Civic (water pump replacement, muffler replacement,
starter replacement, etc.).

1) Is the work involved too much for a “backyard
mechanic”?
2) Do I need any special tools the average “backyard
mechanic” would not have access to?
3) How much will a new radiator be (price range)?
4) Should I purchase a Honda radiator? I know that many times buying
genuine Honda parts, although more expensive, is always better in the
long run. However, I understand that Honda radiators are plastic and
am thinking maybe another type of replacement radiator (i.e., metal)
would be better in the end.
5) Can I do the job in a day? Will I need more than myself to do it?
6) Any other advice you can give regarding the specifics about
radiator replacement in Honda Civics of this vintage. As I understand
it, I need to undo all the hoses (coolant, A/C and auto trans.) and
fans (I think there’s two?) and brackets to get the old one out.
Seems pretty straightforward. And then just reversing what I did. I
also plan to put into a new upper and lower radiator hose and a new
thermostat at the same time.

Thanks for your time,
Chris