snobdds

Where is your time variable? The longer the coolant is in the radiator the more heat is extracted...

xylicon

All these fancy degrees and vocabulary, I'm outta here.

jerry507

The wax compound expands over a 15-20F range, which is what gives it essentially proportional control. It's entirely mechanical but it is proportional control.

jerry507

Also that's the best graphic I've seen in a long time! Haha

RustBucket

iTrader: (1)

Snob, think of the system in steady state. Who cares how cold the coolant is coming out of the radiator? What matters is how much heat is getting kicked out.

Reading the FSM it talks about how the tstat begins to open at one temp and is fully open at another. So yes, it is proportional control. I'm sure someone has a youtube video of a tstat opening in a pot of heating water.

Don't jet-slug outta here yet, it's just getting fun.

jerry507

I've looked around and most of the videos are actually rather poor. I'm going to shoot one this weekend that shows it steady at some temp below 100C. This will at least show the variable nature of the opening, rather than just a simple open or shut operation.

snobdds

Which is a function of time...which the t-stat controls.

RustBucket

iTrader: (1)

Steady state means that we are not considering a discrete time, but just the rates. Basically heat flow (J/s) into the system via the engine balanced by heat flow out via the radiator. I'm talking about the cooling system with the car running at a set speed on the highway.

snobdds

With the variable being time spent in the radiator. Right? Otherwise why have fins in the radiator? May as well just be a tube to connect the upper and lower radiator hose.

Basically, I want my coolant to be in the radiator as long as possible regardless what temperature it enters or exits the radiator. Time spent in the radiator is what kicks out the heat. Which is controlled by the flow rate of the thermostat.

RustBucket

iTrader: (1)

So the thought experiment to try is: what happens if you flow less and less? You could slow to a trickle and have outlet temps near ambient. Why not?

snobdds

Simple...Well first, that is a hypothetical situation that would never happen in real life. Let's keep the context here.

The small valve will open at say a warm mix, I have no idea what temp it opens at, but a warm mix is a safe bet. Therefore, there will always be some flow as the engine warms up. As the temp rises to 195*, then the large valve opens.

Now there is always different loads on the engine. A static state is really hard to have over more than say a couple of minutes, even at highway speed. There is always hills or other factors that make us speed up or slow down. The coolant is always fluctuating temperatures, especially on the warm side of the motor (I.E. leading into the thermostat). The thermostat is always opening and closing (hence) the spring on the thermostat) and controlling flow. The flow rate into the radiator then determines how long it stays in the radiator and then the cycle continues all over again.

It's simple quite really.

jerry507

Yea, it's certainly true that static loads are difficult to come by. Perhaps at idle only.

That basic cycle is pretty simple, however it's complicated by a lot of factors. The opening/closing speeds of the valves, hysteresis and more. There's a reason why temperature issues are one of the number one problems on Yotatech.

Part of the problem is that basically no one actually knows what engine temps are doing. The stock gauge is not particularly good and engine temps seem to move around quite a bit on my truck with the stock gauge not responding at all. These after market gauges seem quicker, but I've seen temp cycles on the order of <60s and xylicon's gauge was still slower than that. I'm not super familiar with capillary gauges, but if you wanted to take it off it would be pretty easy to test the response of it.

As I said before, I'm going to fit a few different thermostats this weekend and take some data from the sender, the ECT sensor and compare that to the stock gauge. At least then people will have some kind of baseline to compare against if they want to solve their problems in the future.

RustBucket

iTrader: (1)

Jerry, that would be really interesting info.

I think the stock gauge is nonlinear. The needle moves from cold to about 180F, there is no movement from 180 to 235F, and then it moves quickly up after 235F. Not sure what temp gets it into the red though

jerry507

It'd be really interesting to take a capillary gauge such as yours and see it's step response so we can compare it to the stock gauge. Do you feel like taking yours out and dunking it in some boiling water?

jerry507

Well, I only got some of the work I wanted done this weekend. First, it looks like my main problem is the temp sender. While it's supposed to be for this truck, the temperature/resistance curve of the thermocouple is a bit off. I'd suspect this is most likely the issue for anyone who has a temp gauge that reacts normally but seems to sit at the wrong place.

The stock gauge actually does seem to be reasonably linear, but only over the range it supports. That seems to work because the thermocouple is fairly linear at the high temperature range. I managed to find out that "middle" is about 50 ohms. 70 ohms puts it about 1/4 from the bottom. Need to test some more points there, especially at the red end. The gauge is also SUPER slow too. It takes MINUTES to react to small changes, so as I suspected you can't really see any oscillation in temperature on that gauge.

I found a really fun way of showing how the thermostat actually works too. Just take your rad cap off and let it idle. This is easier for me to do since I have no fan at the moment, so at idle I eventually overheat (almost let this get out of control actually...) but the net effect is that you get to see the thermostat go full open. I was easily able to see the flow change from a trickle to a full on torrent. The flow smoothly oscillated a few times before I eventually had to shut down. Each oscillation peaked at greater flow too. Classic proportional control response

Other than that my arduino datalogger is working, but I have to finish final wiring in the truck and actually capture the data. That and my Toyota thermostat didn't come in to the dealer Saturday