Oh man, I think it totally depends! Are you touching parts that bear a large energy load? Anatomy with a lot of moving parts? Ballistic weapons? It also depends on when! Did they just wake up from a long nap? Have they been sitting in a garage for a week? Did they just come back from a long trip or battle?
Normal machines can run hella hot, sometimes. Friction, lots of computing, or just plain inefficiency (no shade, gas guzzler mechs!) all contribute to raised temperatures that may or may not actually be pleasant to the human touch. (Omg a mech that overheats from thinking too hard)
I like to think that a sufficiently complex mech could redirect heat energy around their body at will. So if their lil human buddy is cold, they could take their hands into theirs and make em nice and toasty *3*
But more"primitive" mechs who can’t, or whose chassis temperature is out of their control are cute too! Like “oh gosh I was just at the firing range so don’t touch me for a few minutes, sorry…”
Or a mech getting self-conscious about having cold hands all the time? Ugh too presh