From your description it sounds like the car is cooling down when you
are going fast and heating up when stopped or in stop and go traffic. If
that is the case, most likely your radiator fan does not run, either
because the fan is bad or because the thermoswitch that turns on the fan
is bad. Do you ever hear the fan turn on?

Seven wrote:
>
> 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