Why was the first Terminator rotting?

The damaged skin would suffer from rot just like any other skin.

It's also possible that the Terminator, given a short-term job, wasn't taking as careful care of itself as it would have needed to to keep the skin shell alive.

He'd taken a lot of damage, and while it hadn't damaged his endoskeleton, he bled profusely. It's possible that a majority of the blood he'd need to supply his living skin with nutrients, oxygen, etc had been lost.

If that's the case, his entire living skin shell could have been rotting away, unable to live without the blood (and likely other things - when do we ever see the Terminator take a drink of water, or have a sandwich?)

The terminator isn't rotting, its skin is simply getting injured and there is only a slow process for healing/regrowth of skin. The broken blood vessels don't clot quickly, the wounds don't close quickly, and they can fester if not attended to (like any person with restricted blood-flow or a weak immune system). This terminator has received a lot of violence, so its exterior is left in a bad condition.

As the two terminators originate from different timelines it seems that Skynet/the terminator has different mission priorities in those timelines, possibly learned from earlier mistakes.

The 'original' timeline has a terminator that lets the flesh rot whereas the revised timeline (Judgement Day) has a terminator that allows for better care.

Note that in the Judgment Day movie the terminator still rips all the skin off it's arm on command so obviously a direct command overrides a mission objective (minimise damage/maximise stealth.

In Rise of the Machines the terminator suffers only 'minor' damage until the end of the movie so there's not time for the flesh to rot.

The Sarah Connor Chronicles are an alternate timeline so again the priorities for the terminators are different, and given that it is a TV show rather than a movie they would probably not be allowed to explore into the 'rotting flesh' area.

Given the extent of damage the Terminator from the first movie sustained, it was not seeping blood from facial wounds, suggesting that it had already bled out. With no blood in the system, there is no plasma to clot, fight infections, or carry nutrients to wounded tissue for it to regrow.

The Terminator in subsequent films and TV series never sustained that level of damage in such a short time frame. There likely was enough plasma in those systems to facilitate healing, as well as the ability to fight infection.

edit I do realize that we don't see blood oozing from other wounds in other terminators either. In T2, I can assume that maybe the scene takes place after wounds have clotted, and in T:SCC, this could be an edit for the sake of family TV programming.

What you have to remember is that this is science fiction, so "You got a dead cat in there or what?" - can be seem as film filler, however to answer your question:

1. Terminator 1, Kyle explains to Sarah that the T600 model has rubber skin, and were easy to spot, therefore Skynet had to produce Terminators that had "real" skin (well you can't even call it real, it's actually synthetic, but also organic).

2. The T800 has "real" skin, as explained above, it's not real it's synthetic and organic at the same time. Personally I would regard "real" skin in this instance to be actual human skin. Most organic matter rots in the right circumstances. I say this because wood is organic matter but treated correctly, even after it dies, its composition will not change radically over time in the same way that an animals composition would change over time. Again this is open to debate because if you put the organic matter in a cryogenic freezer, it won't decompose very much.

3. Comparing the scene from Terminator 1 and Terminator 2 - In Terminator 1, the Cyborg cuts away several pieces of flesh, including its eye, leaving them to "rot" in the sink. Just put yourself if that hot, humid hotel room in LA, jeez even your sweat might smell like a dead cat! In Terminator 2, the Cyborg is stitched up by Sarah, but remember later on it cuts away the skin surrounding its arm to show Dyson its cybernetic arm, like the one one Dyson's vault at Cyberdyne. This organic matter would probably also rot, but there's no need for film filler at this point in the story!

So it's likely that yes, the skin rots, as would most other organic matter. It's made evident in Terminator 1, just not in Terminator 2 or 3, or 4

To learn more about the skin production process, it is somewhat documented in the Sarah Connor Chronicles, where a Cyborg asks a scientist to reproduce synthetic organic skin.

I'm somewhat of a Terminator geek...it's my favorite film of all time! :-)

Part of basic treatment for serious wounds is debridement; some of the flesh may be dead and in order for the wound to heal the dead matter must be cut away. If you don't remove it the dead flesh will rot, the smell of which draws flies, with maggots soon to follow. Since we saw flies that implies dead tissue and inadequate debridement. Maybe the Terminator had wounds on his back that he couldn't reach to clean, or maybe cleaning his facial wounds properly would have required removing too much skin for him to continue passing for human.

Do not forget what Reese said to Sarah ".. sweat, bad breath - everything" therefore the Terminator sweats when hot. Look at the amount of physical activity it had done recently. It would have sweated buckets and did not bother washing - he needed to roughly pass for human, not get a date. Therefore he would have stunk pretty badly. Also, living tissue surrounding the skeleton (again stated by Reese) had been damaged and, although he can heal - as state in the second film, his wound would still become gangrenous (as stated in the script) if it did not receive hygenic treatment and, as we have established, the Terminator did not bother with hygiene as that was not a priority.

The novelizations for T1 and T2 explain a lot:

• There's a pump for keeping blood pressure
• Said pump was blown away from one of Reese's shotgun shells at Tech Noir
• Terminators heal and heal fast

So he WAS rotting (and also healing just not fast enough to avoid the smell).

Later in the novel when his leg is damaged he ignores it, but considers that if he didn't catch Sarah this time that "mainframe damage would require full attention later", so that supports the idea that he is healing (and that he knows it) and he just doesn't care much at this point.

You'll notice that Terminator 1 has a different haircut in the scene in question compared to the start of the movie, this is because he was exposed to a brief but intense fire while driving a car in a previous scene. I personally believe this is also the primary reason his flesh is rotting and his appearance is "waxy", much of the skin is actually already dead from this fire. Although, the gangrene is probably set in a little quick, but hey, it's Hollywood.

The first shotgun blast that Kyle shoots off hits the T800 in the arm. The t800 was insanely close in completing its mission. The hard baller goes off just shortly after Kyle blasts him the first time. I’m sure that Kyle also damaged all the rudimentary organs that are housed in the “abdomen” section of the t800. I’m also sure that when Kyle has knocked down the T800 and knocking if offline for a short amount of time. There is evidence that when the t600s were more common, that you can permanently knock one offline permanently and can be reprogrammed far easier than later models. That’s why the 800 “boots up”.