After getting myself a new improved Indiana Jones Jacket recently, it made me think: He wears this thing in the jungles of South America and the deserts of Egypt? Now, true, it was made of a very light leather (much lighter than you would think), but it’s still a dark leather jacket.
The caption at the opening simply says “South America 1936”. The Amazon basin has an average year round temperature of 80 degrees Fahrenheit (26.6 Celcius) with 90% humidity making for a heat index of 86F (30C) though the largest region (the Brazilian region) averages from 80F to 90F (26.6-32.2C) and again, the humidity will make it feel much warmer. Now true, the night time can be cool, again made to feel cooler by the humidity, but if he’s going on a trek after a fertility idol during the day, I would think he’d leave the jacket.
The Egypt scenes are a bit more plausible because when we see him walking around during the day, he does not have his jacket. The first time we see him wear it in Egypt is at night when he goes after the ark. Then he gets trapped in the Well of Souls by Belloq, and by the time he escapes it’s day again (which doesn’t seem to add up to me either, not to mention that he “escapes” by pushing out a loose stone that exits right next to an airfield the Nazis are using and yet they never checked what was in there…), and from there gets on a horse and goes after the truck with the ark on it. So I can buy that the desert gets cool at night and he wasn’t planning on wearing it during the day but then got stuck with through circumstance but even then he could have left it with Sallah and Marion before running off after the ark. That thing had to be hot in the Egyptian sun.
Lastly, I don’t know what kind of garment cleaning procedures they had in 1936, but that thing had to be pretty rank. I know how bad it can be just to be in the car with myself after an outdoor band gig, much less gallivanting around the Egyptian sun in wool pants, a long sleeve cotton shirt, Leather shoes, felt fedora and a lambskin leather jacket. I think the scene on the submarine where Marion is helping him undress and lay down in bed would have been more like, “Here, let’s get you…OH, GOD, JONES! You REEK! Do they have a shower on this sub? I mean, I’m all for sexy time but how about we begin in the shower?”