the importance of thermostats

Interesting. I had not seen anything like thermo #1 before. Thanks Jim.

That is not cool.

Paul in Houston TX wrote in news:l0t0lu$7al$ snipped-for-privacy@dont-email.me:

Both designs have been in use for decades.

"Bypass" cooling has been used since thermostats came into use, and well before emissions controls were ever heard of: it's the only way you can get a thermostat to open before the engine destroys itself.

Some systems left the bypass open all the time (#1; early '70s Toyota), counting on the diametric difference between rad hose and bypass hose to bias flow to the rad hose, and some systems used thermostats that blocked the bypass once the thermostat opened (#2; early '70s Mazda), forcing 100% of the flow through the thermostat.

Either design will experience overcooling when the thermostat is removed.

Concern for emissions -- specifically nitric oxide -- around 1990 resulted in a major change in cooling-system design that had nothing to do with the thermostat itself: The original U-shaped fluid path gave way to the straight-line path that all engines have today. The reason for this change is that the U-shaped path tended to cause the rear cylinder (bottom of the U) to run hotter than the others, making it more difficult to control emissions of nitric oxide; a straight-through path provides more-even temperatures throughout the block.

true.

not true.

nope. see above.

absolute nonsense.

hardly any thermostat is open all the time. and they seldom rely simply on "diametric difference".

i don't know which mazda you have in mind, but ones i've seen, that's not true. the whole point of a "bypass" system is that it is in fact, the primary circuit that flows all the time, and the cooling circuit is secondary - that works only when required.

absolutely not true. the whole point of my post was to illustrate precisely that.

started being implemented in the 80's and researched in the 70's. your integra is an example of that.

nitrous.

the kind of cooling circuit you describe is antiquated and dates back to "convection only" cooling circuits, even though it continued to be used until about the 70's. and nitrous emissions are the least of your concerns with it.

One day when I was working on some related issue, I talked to a GM engineer, and he told that running without a thermostat could indeed overheat the engine, but his explanation was that the coolant would move through the radiator too quickly for it to cool properly. I would think that it's possible.

so, [logical thinking exercise] if it's running through the radiator too fast to dump heat, how is it running through the engine slow enough to pick up heat in the first place?

hint 1: the average radiator has a much greater surface area than the average cylinder core.

hint 2: sufficient mass transfer with a small temp delta can out-cool lower mass transfer with a higher temp delta.

When the ambient is about 115, there's a continuous sun load, and the engine is under load, I can see it.

you can see reduced delta, but that doesn't change the equation because it would be common to both circumstances. the point is, faster flow doesn't stop the engine cooling, it's misdirection of that flow that causes problems - it's two circuits and no valve directing how much flows in each one.

Bill Vanek wrote in news: snipped-for-privacy@4ax.com:

It's not true. Any reasonably-modern engine will UNDERHEAT without its thermostat. Go ahead, try it yourself. I have.

For typical engine cooling (not the bypass method you mentioned) logic says the more flow the more heat transfer, the cooler the engine runs. You're not going to get turbulence from the typical water pump that would lessen heat transfer. So unless he's talking about something "atypical," That GM engineer was just wrong. Maybe he's a suspension engineer.

It's all good to point out any "bypass" cooling that would overheat an engine with the thermo removed. How about some examples of brands?

Personally, I've run a couple of old cars without thermos. But I was ignorant. And it probably did little harm. But it's been a long, long time since I learned that modern engines are designed to operate best within a certain temp range. So I would do all I could to avoid running without the specified thermo.

But I didn't know about this bypass system in any car I'm familiar with (not many). So I wouldn't expect overheating by removing the thermo.

Some here, not you, do not understand the principle of flow in parallel circuits. The resultant resistance (and accordingly the flow) follows the rule of the reciprocal of the sum of the reciprocals. One way though that overheatring can result from an absence of a thermostat is hose collapse on the suction side, caused by increased flow rate. A spring in the hose can be one method of preventing that problem.

using an electrical analogy for fluid flow is way too simplistic. there are some very rudimentary parallels at low flow rates, but because fluids have mass, they have momentum, and they also experience turbulence and cavitation. all three factors can completely obliterate any simplistic "electrical" analogy - venturi effect for example.

not a differentiator - can happen with any pumped system.

????

indeed, it's entirely engine specific.

as to brands, the honda 4-bangers are big into the bypass thing. but my old 22r toyota is not. if you look at the pics of the two thermostats i posted before, you'll note the secondary diaphragm on one of them. that helps control the secondary circuit flow on a honda bypass circuit.

Vic Smith wrote in news: snipped-for-privacy@4ax.com:

You're correct in that higher flow /does/ result in better heat-transfer.

The thing that improves heat-transfer the most is the "temperature gradient", which is the temperature difference between the warmer (water) and the cooler (air) sides. The greater the difference, the /steeper/ the gradient; the greater the difference, the greater the transfer of heat.

Think of a playground slide: the steeper the slide, the faster your kid goes down it, and the geater the number of kids that can go down the slide for any given time interval. The /flatter/ the slide, the slower the kids go down, and the fewer the number of children that can follow each other down for any given time interval.

Modern cooling systems are designed to operate with a steep gradient, but one that gets flattened a bit by the thermostat when necessary. Remove the thermostat, and the gradient /steepens/, resulting in even /better/ heat- rejection into the atmosphere. Eventually you get too much of a good thing.

Turbulence /improves/ heat-transfer. The more turbulence the better. Turbulence can be effected by applying a texture to the solid surfaces, or by increasing fluid-flow, or both.

Turbulence strips away the boundary layer that tends to form between solid surfaces and cooling fluid. The boundary layer acts as a sort of insulation. Insulation works by flattening the temperature gradient, which results in /less/ heat transfer.

It is true that an always-open bypass can affect heat-rejection by allowing some of the heat to recirculate back into the engine, but that would actually eventually /steepen/ the gradient at the rad/air interface, canceling any deleterious effect of the open bypass. However, an open bypass results in less precise control over cooling system operation.In any case, an open bypass certainly does NOT cause overheating.

in order to cool, you do indeed need a temperature delta. however, a "steep" gradient indicates an insulator and thus little cooling.

too simplistic.

you mean high transfer.

transfer rate increases. you can have a high heat transfer rate with a low temperature delta, if the mass transfer rate is high. that's how the fan on a car radiator works - you step up the mass transfer rate to increase the heat transfer rate. it's important to understand that you can't "increase" a temperature delta to assist cooling - atmospheric temperature is whatever it is.

increased flow improves heat transfer. turbulence, by definition, contains random elements that can upset transfer.

increased flow. texture increases surface area - another factor entirely.

turbulence can thicken it.

conductors flatten the gradient, insulators increase it. if you have no gradient, then everything is isothermal.

delta, not gradient.

right. because it's short-circuiting the radiator.

doesn't mean there's heat transfer. if it's insulated, you have an even bigger delta, but there's no cooling.

an open bypass that short-circuits flow through the heat exchanger, the radiator, will most definitely cause overheating.

Try this:

thanks, i already have one.

I doubt it.