Maybe someone can help me on here. First let me say sorry if I put this in the wrong spot. A friend recently bought an 89 iroc 5.7 tpi. Unfortunately, getting a hold of the previous owner is not possible. Which sucks because I have many questions. And of course, my friend doesn't know the difference between a nut and a bolt, so he has asked me to help him with the overheating issue. I am no mechanic, I am a long line fishing captain but I have always liked to turn wrench on bikes/cars/and now 4x4's for fun. Now that all that is out of the way..

The previous owner deleted a bunch of stuff. For starters, there was no overfill reservoir for the radiator. A small cap on the radiator where the overflow hose connects. And another medium size (same size as caps on tb/intake manifold) cap just below where the upper radiator hose connects to the radiator. Caps on both ports on the throttle body, cap on the intake near the throttle body, and a plug on the top of the water pump. (Is that a bypass port on the top part of the water pump?) So basically there is an upper and lower rad hoses and not much else. 2 electric fans always running with engine. And no thermostat. I ran the system without the t-stat installed and the rad cap off to see how the water pump was working. Really strong flow.

Living in Hawaii, I have owned half a dozen Chevys all with the 4.3 and I believe I ran every one without a thermostat just fine. Although my 93 4runner ran poorly without a t-stat, it never got hot. Since its the endless summer out here, I think the caps on the throttle body should be fine. Unless I'm mistaken, the water ports on the tb are there to warm it up, like during the winter.
So I installed a new thermostat, overflow reservoir, and temp sensor (2 wire, sends ecu eng temp) on the front of the intake.

Now the part that just baffles me. The gauge would rise slowly until it reached around 180, then wouldn't show any hotter as the eng temp rose. Until after it was overheated, then would jump up almost pinning out.
So I set out to fix the gauge, and what I found is something I've never seen before. I bought a new sending unit (single male spade connector) and installed it in the drivers side head between plugs 1 and 3. What I unscrewed from there looks nothing like the replacement part (which after a lot of research I am certain that I installed the correct part). I am almost certain that the prev owner installed a knock sensor instead of a sender unit. (Also I should say that I verified that there is a knock sensor installed low on the passenger side in the block between the motor mount and the starter). I think the wire for the gauge is green, with a single female spade connector that was connected to the round terminal on the knock sensor.
Now when the car starts/runs the temp gauge is automatically pinned all the way up. It's like it works better with the knock sensor and not at all with the new sending unit.

Also I checked diagnostic port and no codes are stored. So has anyone heard of this before? I didn't get a chance to put my meter on the ks and sending unit side by side to check ohms and compare. Maybe the ks and sender unit are similarly made.. Anyways any help would be welcome.

I've looked for diagrams for the coolant system but surprisingly hard to find a good one. What I understand so far is that there should be a short hose from tb or intake that connects to a valve located (sorda suspended) toward the front of the passenger valve cover. Then from that valve, a hose to the heater core. I'm guessing that's in the dash somewhere. Looks like he deleted the whole heater hose system.
How much water does that take away from the system?
Does the amount of water lost from the deleted heater hoses have an effect on the cooling process?
Or is it too minimal or closed off to make a difference?
If the heater hoses are installed correctly, does the water in that part of the system circulate with the open t-stat or only when running the heater/ac?

​​​​​​Is the gauge just a single wire like the sending unit? ​​ I'd like to get the gauge working without tearing into the wiring. Could I run my own wire from the sending unit to the gauge?

Also what is the black box above the passenger side valve cover? It has 3 black hoses, (not sure if they are for water or air, but they are about the same size as the heater hoses) 2 coming out of the back and routed toward the firewall, and 1 short hose on the side. I'm guessing pair reed valve or egr, something like that.

Last question. Is there a better manual for this car than Chilton or Haynes? I have the factory service manual downloaded for all my Toyota's and it would be great to get something like that for the 'maro. I searched briefly with no luck, hoping someone knows where they stay.
​​​​​​​Thanks for any help