So what are your ingredients and what is the mix ratio?

When I start a hot pile, I mix fresh cut grass and or moist coffee grounds with shredded leaves in the right proportions and it reaches a hot temp in three days.

Both fresh cut (and I mean cut within hours of being cut I use it) and used coffee grounds are right at C:N ratio of 20:1 and mixed dry leaves are around 45:1 (guestimate). So 1.5 pounds of the green to one pound of leaves, should give a overall C:N ratio close to the optimal 30:1.

This mix often does not need moisture, but it doesn't hurt to add a little when starting the pile. My shredder reduces the leaves to about 1/8", so it shreds more finely than most chipper/shredders.

I make the starting pile in one day. If you never start with a full size pile, but only add small quantities to get it up to 3'x3'x3', expect only lower temperatures. You only get temps of 140-165F when all the ingredients are started at once. You can add ingredients after the start; I usually put my more smelly stuff (fish parts, veggie and fruit wastes) into the center after the pile heats up.

You do appreciate do you not that heat is derived from how the pile is breaking down.
You cant just throw a 2" layer of grass clippings in on Wednesday and expect any kind of heat in the pile on Sunday.
Different materials break down at dfifering times and in different ways.
Grass clippings, to be sure, is a good nitrgoen producing add-in to produce heat. But give it time to work.
How much bacteria is it generating and what other materials might be cooling it down.
All piles need to be kept damp....so when you water your pile take it that you are also cooling it and untilt he pile heats up, it will take time to generate the heat as before.

How much your compost will heat up will depend on the ratio of material, the amount of moisture in that mix (too much water displaces air that is also needed by the bacteria), and the total volume of the compost. That size is the bare minimum to get enough bacterial activity that is what generates the heat, and in my experience that size seldom gets very hot, because the volume just is not there.
You need not have internal compost temperatures in the 140 degree range since your material will be digested just as well at those lower temperatures.

I only have about 4 months experience, but I'll share my opinion for what it is worth.

Robert hits the mark pretty well with what he writes -- I followed his lead and gave up on a bin 3' tall because I couldn't reach the bottom. His success with 2' tall mirrors mine, now that I finally reached a full bin.

That said, I routinely hit 140 degrees in the top half of my pile even though I didn't start it all at once. I've never exceeded 140 as far as I know, but even when the pile was only 12 inches deep, I saw 120 to 130.

Kimmrs has lots of experience, but I disagree with the minimum size mentioned. My 1/2" hardware cloth bin is 2' tall and is a bit more than 2' in diameter.

I made a new bin 2' tall and a bit over 3' in diameter and it looks massive to me. I can see the advantage -- there is a lot of surface area for making additions -- but considering how it took me 3 months to fill the other bin, the 2'x3.25'Diameter is too daunting to even consider filling.

Good luck.

You can get high temperatures in smaller piles of material, if enough Nitrogen is added to the mix. A small pile of just grass clippings will get quite hot, but that does not good compost make.

You can add high nitrogen lawn fertilizer (urea) to the pile and it should heat up nicely.