No, Chief (KC that is), the thermostat (in the rotary application) does not slow down the coolant in the rad until LESS cooling is needed. As more cooling is needed the thermostat INCREASES the flow through the radiator.

If you leave the thermostat out of the rotary, LESS water goes through the radiator because it short circuits through the bypass. In essence the thermostat is a thermostatically controlled proportioning valve.

It ain't a Chevy unless you make it a Chevy. There is a forum for that process too.

 

No, it really isn't.
I think we have an "apples/oranges" situation here.
You have control over many more variables in the HVAC system than is possible in a car application.
You can control the airflow over the heat exchanger and also the rate of fluid flow.
Our airflow is wildly variable and the pumping rate is rigidly linked to engine RPM, changing not in response to coolant temp but rather engine speed.

Going back to the dump truck analogy- sorry- if you "slow down the water in the radiator" and allow the truck to shed more heat, doesn't it also mean that the truck is traveling more slowly in the engine, thus picking up more heat to get rid of?

Also, you have a single circuit coolant loop- pump>heat exchanger>pump (and whatever piping/reservoirs are necessary in between).
The RX-7 (and most modern cars, for that matter) have a dual loop (or maybe more accurately, a "one and a half" loop)...one circuit endlessly circles the engine passages and the thermostat selectively diverts a portion to run through the radiator loop and return to mix colder fluid into the main loop.
It maintains the desired ratio of cold/hot water not by selectively "slowing down" some molecules (and really, if you think about it...how does a water molecule "slow down" when it would be beneficial and then recognize the appropriate place to "speed up" when it's being pushed by a pump that isn't even aware of the coolant temp?) but by varying the volume of cold to hot water.
Just like a shower control.

I'm probably just being pedantic at this point.

 

Yep, pedantic...

But I was basically going to come in and post the same thing, thanks writing all of that for me.

 

In your example you compare the heat exchanger in an HVAC system to the radiator of the car. Fair enough. I will assume you are comparing a hydronic system.

Now tell me, if you have a constant CFM of air in your system, would you decrease (or slow) the volume of water through that heat exchanger in order to increase the BTUH transferred to the air? Because if you would, then you should also believe that one needs to 'slow' the coolant flow through the car radiator.

If you take this to the illogical extreme, the less hot water you pass thought the heat exchanger of your hydronic HVAC system, the more BTUH you will get out of it. At some point we will flow NO hot water and attain INFINITE BTUH.

Now do you get it?

 

Dunno if the above is all miscommunication or what, but higher flow means better cooling, lower flow means less cooling. "Spending more time in the radiator" means nothing because coolant is always in the radiator 100% of the time. Likewise restriction does nothing except slow down the flow of coolant. Hotter coolant releases heat faster than coolant that has already been partially cooled off. Better for the partially cooled coolant to loop around again and dump heat the next time it's in the radiator, rather than sticking around to release less heat than you would if hotter coolant was coming in sooner from faster moving coolant. You always want the thermostat to be as unrestrictive as possible when open, bar nothing. Only thing it should be blocking when open is the bypass pathway.

 

If you are "slowing down" coolant flow through the rad to allow the fluid more time to be cooled by airflow, other coolant that isn't in the rad is in the engine, building up more heat load - and there is a definite limit on how long that can go on. If more cooling is needed, the thermostat allows more flow through the rad. If that doesn't keep up with cooling needs, the fan clutch engages to use the fan to pull more more air through the rad, to cool the fluid more as it passes through.

In any event, the main point is, removing the t-stat actually decreases cooling efficiency - it allows coolant to flow through the rad even at low engine temps, causing the engine to run richer longer, and increasing wear by increasing oil contamination with unburnt fuel and other products of inefficient combustion. Moreover, no thermostat means coolant flows through the bypass when the engine is hot and in need of additional cooling, so less is flowing through the rad and being cooled, and instead the hot coolant goes back through the block without a chance to dump it's heat load in the rad.

 

Hi, it's me, the pedant, again.

If you are "slowing down" the coolant in the rad, you are performing a miracle and the Nobel committee should be notified.

The reason I harp on this subject is that grasping the operating principles allows one to make reasonable diagnostic assumptions.
If one buys into the "slowing down/restrictor" theory, as Jack pointed out, it would make sense to "restrict" flow to the rad to decrease coolant temps.

The thermostat is NOT a restrictor and DOES NOT slow down anything.
It's a diverter valve, coolant flow is constant, it simply changes where the coolant goes- either back through the engine or an entertaining side trip through the rad.

If one suspects that the little dump trucks aren't able to dump their loads, you absolutely cannot "slow them down" through restriction, but you can increase the time they spend in the rad...by lengthening the path, i.e., get a larger radiator.

A second approach would be to increase airflow over the heat exchanger- higher CFM fannage and/or better ducting (make better use of the airflow you already have).

A third approach would be to increase the differential between the coolant temp and the air you're asking to absorb the heat.
The greater the delta between the two, the more efficiently the coolant can transfer energy (heat) to the surrounding medium.

A sterling example of this principle at work is water/alcohol spray on an intercooler. Mist the intercooler and IAT drops...not because you restricted/slowed down the air flowing through it but because you increased the capacity of the cooling air to absorb heat.

There are so many factors actually in play in a cooling loop that you can't afford to jump down a rabbithole of erroneous fundamental assumptions when a problem crops up.

 

Interesting dicussion... I don't agree with everything said. But it's true that you want you the flow as fast a possible. This way, the temperature gradient is bigger and the rate of heat exchange is faster.

But about my problem, it has nothing to do with the thermostat. I bleeded the system with a funnel only to see a constant stream of bubles coming out, and even some smoke when I rised the RPM: I think I'm screwed.

I don't really feel like opening the engine these days... time to sell the car

Oh and yes Jack, I'm a Canadien Français.

 

I just got my engine rebuilt by RP and I had a similar problem. I wasn't ingesting coolant but I was getting exhaust gas into the cooling system. My 19yr old coolant seals where still intact, but in fact it was my front iron that was cracked.

Speaking of which I need to update my rebuild thread...

 

Nous sommes frères jumeaux de mères différentes ...