Is 4 days enough to discover Iceland's Ring Road and Golden Circle by rental car in late March?

No, 4 days is (way) too short for tourists and especially in the winter.

Yes, you can probably drive around the ring road (Route 1) in Iceland; it's 1,332 km and the Golden Circle is only 300 km. The roads are paved, in good condition, and the maximum speed is 90 km/h (with a few exceptions in villages). That means that with ~5 hours driving per day, you should be able do to the trip, right?

First of all, you're at 64/65 degrees latitude. Mid-winter, that means only a few (3-4) hours of daylight, but you're going in late March, so that means 12 hours of daylight. Still, expect snowfall when you drive (you have no experience with that, so please rent a 4x4) and some parts of the road may be closed due to floods, excessive snowfall or mudslides. The Icelanders will try their best to keep the road open, to prevent villages from being isolated, but Icelandic weather can be very unpredictable and violent at times. Which means you're better off staying in a village for 1-2 days; you don't want to miss your plane because of that.

Even if you do manage it, you won't have time to enjoy all the sights and venues along the route (and there are many). I've traveled the Ring Road (without the Golden Circle) in 8 days a month ago (actually, two thirds of it, I went back via the F25, which is closed in winter); that was really enjoyable but it was during the summer. I have no experience myself in winter but I heard from locals (and read on the Internet) that one should plan at least 2 weeks for such a trip.

Regarding safety: Iceland, especially outside Reykjavik, is virtually devoid of criminals; I left my valuables in the car and even forgot to lock it sometimes. Cell phone reception is adequate along most of the Ring Road. It's absolutely safe, please enjoy Iceland with the three of you but do it at a slower pace :)

I'd say that's plenty of time for the Golden Circle, but not nearly long enough for the ring road. I went around the ring road in about 8 days in late September a couple years ago. It felt a little rushed to me. There was a lot I wanted to see, but didn't have time to visit because of the distances we had to travel. It also usually took longer than what Google Maps indicated.

If you only had 4 days, you'd be driving most of the time with little time to do anything else, and that's during good weather. I've found that when traveling, it's better to not be too ambitious and have plenty of time to see things.

By the way, I recommend the local municipal pools found in many towns. They were quite nice and affordable. The water is very well heated (even the "cold" pool was quite warm), and we enjoyed the outdoor pools even when it was around freezing outside.

We traveled to Iceland a few years ago. In a sudden storm one windscreen wiper got stuck, and then got ripped off in the wind, at another point the handbrake on the car froze solid then got stuck so we couldn't release it.

While you COULD do this journey like this, you really want far longer. If you're in Iceland for 4 days, you could visit the geysers and the beautiful waterfalls, and likely see the northern lights too. (Though this might not happen; it's very variable! We managed to see it almost every night in February.)

We drove around the Ring Road in 5 days in early April, 2017. That did leave us time to do sight-seeing and enjoy the trip, but trying to take it even one day shorter would have certainly felt rushed.

Our trip was

• 1st night - Reykjavik
• 2nd night - Hrafnagil
• 3rd night - Myvatn
• 4th night - Hofn
• 5th night - Kirkjubæjarklaustur
• 6th night - back to Reykjavik

(We also spent a couple days in and around Reykjavik on either end, so there was decompression time in there.)

Weather permitting, you could drive from Reykjavik to Myvatn in one day (7 hours or so), which brings you to a four day/five night trip. So technically, yes, it's possible.

But, even though that was a couple of weeks later in the year than your plans, we still ran into a blizzard (by Icelandic standards!) on the north coast. It didn't end up affecting our schedule, but I can tell you that driving 300 km over near-deserted, icy roads was not great fun, and it would have significantly impacted our trip if the blizzard had started a few hours earlier or lasted a couple of hours longer.

I learned to drive in Canada and am reasonably experienced with winter driving. Given that you say It is my first experience of driving in the winter then I would say by no means is this a good idea.

The other answers present valid concerns (notably winter conditions) and many reasons why someone may want to take longer to enjoy to its fullest the trip.

I'm going to go the opposite way and take the assumption that if you say you rent a car for 4 days, that's because that's the longest you can spare. After all Iceland is a very expensive country for a foreigner and you may be there only for a week in all.

I personally did the Ring Road in 4 days (3 nights) in late October, my first time in Iceland. I had spent a few days in Reykjavik and touring the Golden Circle, but wanted to hit the road and see what the country had to offer, far from the main tourist attractions. The lady at the car rental company was horrified. I had to drive 5-7 hours per day, but I still had time to hike every day. And let me tell you, as someone who enjoys driving, I had more fun driving the South road between the sea and the glaciers and the many waterfalls, than I had hiking in marked trails.

There are many (and I mean many, as in one every few kms) small stops on the side of the Ring Road. We're talking small patch of dirt for maybe 2-3 cars tops, but enough to stop for a few minutes and enjoy the scenery before moving to the next one. To me this was the height of my trip. YMMV of course.

So assuming that you cannot spare more than 4 days for the Ring Road, but still want to see as much as possible of Iceland, and that long drives in relatively tough condition don't scare you, even excite you, then I recommend it. I also recommend doing the full circle: the South takes longer, but was the best part by far. Going back by the North saved time on the return trip. Do check the conditions prior to your trip, you may need to get back the way you came if the roads on the North side deteriorate, as mentioned by @Willeke.

Go for the all-wheels drive though.