Got a detached 3 car garage, the doors barely get sun light, just a few hours in the morning. Majority hits the roof and sides.

Was curious if I added insulation to the walls of it would help with the temperature swings? It's completely unfinished, side sliding window that I leave cracked and about 15ft of ridge vent is the only airflow it sees.

If not, any other ideas?

Simple answer is YES it will reduce the temperature swings. Question is how much are you willing to spend? I just finished doing about 400 sf of R38 ceiling insulation and it cost about $450. So depending on how many square feet you're talking about it could get pretty pricing.

That was going to be my follow up question....is it worth the price?

Plus I don't plan on doing the ceiling so not sure if it's still worth it to just do the walls.

Figured doing the walls around the beer fridge could be beneficial

Since you're not spending money on heating/cooling the structure then obviously there's no energy cost savings, but I still think it worth doing some insulating. Definitely around the beer fridge - don't want to make it work too hard!

Since you normally use a lower R-value in walls it won't be as expensive/SF and any insulation at all will certainly help. Especially would be beneficial on any outside walls facing west or south.

Appreciate the input

Unfinished, detached and exposed framing? I'd probably work on ventilation and air movement rather than insulation. Powered roof or gable vents or a BAF ceiling fan.

Only venting is ridge vent and side window. It honestly doesn't get unbearably hot just figured if I could improve it, why not

I've got a very similar garage setup. Three car detached, mostly unfinished (previous owner had builder sheetrock the walls and ceiling of one bay, and insulate the walls). Only two static vents in the roof, no other ventilation. Garage could reach 120F+ in the heat of summer - often 15+ degrees warmer than the outside temperature.

My garage doors faced the afternoon sun - I started with insulating those and noticed some improvement, but nothing huge.

Then I insulated the remaining walls. No noticeable difference.

Next, I replaced the siding, eves, soffits, and roof. Eves were replaced with Hardie, which is fully perforated for ventilation, and the static vents in the roof were replaced with thermostat controlled powered attic fans. Now, the garage doesn't get warmer than the outside temperature.

Honestly, without closing in the ceiling and/or adding insulation or radiant barrier between the roof and the ceiling joists, I think this is about the best I'm going to get.