Coolant is still running too cold?

[dom14]

Well, if it's pumping it FROM the bottom of the radiator, to the thermostat, your reading is always gonna be low isn't it?

Not always. The reading will be the highest you get until the thermostat opens. When thermostat opens, you notice a 'sudden' drop in temperature for few seconds. then it will rise again.

Won't your reading be cold, with the colder water coming from the radiator that's being cooled as you drive?

Yes, that is a valid argument. That's why the temperature sensor is inside the ancillary hose next to the thermostat housing, which comes directly out of the engine block behind the thermostat.
So far, I've got the highest reading from the current location, which is behind the thermostat in the engine block.
I believe the test speaks for itself.

If it's on the top hose, you'll get the hotter reading no?

Yes and No. Yes, because the hot water from the block rises to the head via thermosiphoning & pump assistance.
But, the heat obviously spread around the aluminium head quickly. So, NO because of "thermal efficiency" of the the aluminium head. That's why I believe the temperature reading I got from the coolant port on the cylinder head(from the radiator top hose) wasn't any better than the reading I've got from the port behind the thermostat on the engine block.

The water would be coming out of the engine, and into the radiator no?

Yes, just as I painted in my rough sketch.

I've noticed since changing the thermostat in mine, it sat a little higher temperature wise (80-82), used to sit on 78-80, both 77c thermostats, though I was towing a camper and had a kayak on the roof..

You did it right.

I'm simply more interested in getting the temperature reading from more than one place to device a good failsafe idiotproof warning system(for the idiot, which is me, 'cos I'm pretty good at "falling asleep" on the wheel or daydreaming while the engine's getting cooked from overheating. it's genetics, don't blame me. )

I guess, as a final question, if the coolant flow is coming out of the engine to the top hose of the radiator, then down to the bottom, through the thermostat and back into the engine, wouldn't the thermostat be closing because of the cooler water coming from the radiator? Or do I have this all backwards?

No, it's a pretty damn valid intelligent question. The 'cold' water that enters from the bottom of the radiator into the thermostat housing aren't that "cold" after all. Then there's enough heat behind the thermostat 'cos the pump circulates water inside the engine block(and head) from front to back. That would be enough heat to keep the thermostat opened once it's opened.
And yes, if the outside the temperature is sub zero, thermostat can shut from the "cold" water entering from the radiator, and that's way it should be, so the correct temperature inside the engine block & cylinder head can be maintained. But, that's not likely to happen in Melbourne(don't take my word on it though, I ain't gota degree in engineering thermodynamics yet ).
Overall, it's a reasonably efficient cooling system design, 'cos lot of thermodynamic experiments precedes these cooling system designs.

Imagine if they design it the other way around. Coolant enters the engine from cylinder head coolant port and travels down to the engine block towards the thermostat on the engine block. That won't do a lot of good in this particular engine design, I think, 'cos this aluminium alloy cylinder head is NOT that good with handling temperature fluctuations and can crack over time from thermo metal fatigue.(my wording). So, that's why I think Nissan engineers designed the direction of coolant flow the way it is.
Having said that, there are engine designs out there where the thermostat is on the cylinder head and the direction of coolant flow even may be the other way around. It all boils down to the way the engineers design the coolant system accommodate the thermal efficiency of whole engine.

Another thing is that even though these coolant system designs are good for what we pay for the vehicle, we can improve it a lot by installing aftermarket systems like "Davies Craig Temperature Control Systems" using electric water pumps and clever electronics. These things are in the market, I think, 'cos good engine performance and longevity comes down to heat management at the end of the day(This is why I might have come out as a bit pedantic with this temperature measuring thing). Browse through below links for more info.

https://daviescraig.com.au/switches-controllers

https://www.sparesbox.com.au/davies-...Q&gclsrc=aw.ds

https://daviescraig.com.au/media/921...er14.01.15.pdf


One last thing I thought I should mention here is that the thing we do by pumping cold water into a leaking and overheated cooling system is many times the very thing that can cause the cracking of the aluminium alloy cylinder head or even the cast iron engine block. I've seen that happened more than one time(yes, I have seen a cracked cast iron block from pouring cold water into it). As a matter of fact, I believe that's how I managed to crack few places of my cylinder head back in 2011, when it overheated due to a burst coolant hose leaking the coolant. I grabbed the cold water from the back of the car and poured it straight into the badly overheated cylinder head through the radiator. That must have caused further damage by suddenly cooling down the badly overheated cylinder head. The best thing we can do to an overheated engine is to stop it and let it cool down by itself. NOT pouring cold water into it to cool it down.

P.S.
Your question still makes sense. I just discovered the coolant flow direction that I sketched in the diagram earlier was NOT correct between the heater core and engine block. The ancillary coolant port next to the thermostat on the engine block actually receives water from the heater core(not sending water out of it). I've corrected the final diagram as below.
I will also move the sensor from front ancillary hose port to the back ancillary hose port of the engine block, and see whether it can yield a slightly higher temperature reading. Logic says it should, as the current spot at the return line of the heater core should be slightly cooler. I will update the outcome soon.