On 8/1/21 4:01 am, Arlen Holder wrote:
> On Fri, 8 Jan 2021 00:05:24 +1100, Xeno wrote:
>
>> The lower temperature thermostat would run the engine cooler by 15
>> degrees and that would increase intake air *density* resulting in more
>> power. For a performance application, the 160 thermostat might even gain
>> a little more power - for the same reason. Note too, running the engine
>> cooler means you have more leeway in the risk of auto-ignition of the
>> end gas meaning less risk of detonation. You can get away with either
>> more spark advance and a higher compression ratio.
>
> Hi Xeno,
>
> I do NOT profess to be an expert in this topic, not in the least, so be
> patient with me if I state what seems obvious & logical to me but which
> might not be the case in reality (for today's engines).
>
> The thermostat, as I was taught way back in the early sixties, opens up
> _once_ (in general), and stays open for the duration (until the engine
> shuts down).

You need to appreciate the two (2) primary functions of the thermostat;
it gives a faster warmup and maintains a *minimum* operating
temperature. What the thermostat does, therefore, is totally dependent
upon the capacity (efficiency) of the cooling system. That means, if the
cooling system capacity is greater than the needs of the engine, even
under maximum power, maximum load situations, the thermostat will
continue to *restrict* coolant flow. That means it will have to either
*cycle* or, alternatively, maintain an *intermediate flow restriction*
position.
>
> In fact, once an engine is "warmed up", I was taught you could completely
> remove the thermostat, and you couldn't tell, from the outside or from any
> measurement parameter, that the thermostat wasn't even there anymore.

Nope, remove the thermostat and you have *no control* over the minimum
operating temperature. All cooling systems are (or should be) designed
to provide *excess* cooling capacity. That provides some leeway as the
cooling system progressively degrades through blockage and buildup over
time.
>
> At least that was way back when...

Beg to differ, it never was like that. The engine would run *cooler*. In
fact, even a working and fully open thermostat provides some *extra*
restriction over an absent thermostat. What's more, some thermostats
provide a facility to block off a bypass passage once the engine has
warmed up. Removal of the thermostat on engines so designed will cause
*overheating* with the thermostat removal since the bypass flow is not
being blocked off as it should be thereby preventing a percentage of the
coolant circulating through the radiator.

https://www.are.com.au/feat/techt/thermostat.htm
>
> Fast forward to today and emissions controls, I understand that today's
> thermostats may be much more finely mapped such that they might open up a
> few times during a typical drive; but do they?

Yes they do. It is for the purposes of emissions control that we have
high temp cooling systems. For pure power without regard to emissions,
cooler is better (160-170F)
>
> If they do, then my comments below are moot, as the "lower temperature
> mapped thermostat" could perhaps maybe affect the engine temperature (if
> it's constantly in the never ending process of opening and closing and
> restricting coolant flow).

It could well remain, for example, in a half open position during normal
running if the temperature of the engine remains consistent.
>
> But if the thermostat opens only once (given an engine runs hotter than the
> thermostat set temperature), then wouldn't a lower temperature thermostat
> simply mean that it opens once, but at a cooler temperature than before?
>
Will affect the engine *minimum* operating temperature. In effect, this
should be the *normal operating temperature* of the engine. If the
engine runs hotter than this, then the cooling system capacity is either
insufficient or has been compromised by buildup of sediment, corrosion
or insulating layers on the radiator internals.

On the topic of why you might run a cooler thermostat than OEM for
racing, this link might provide the answer.

https://www.reischeperformance.com/WhyLowTemp.html

Supports points made in my original response.

--

Xeno


Nothing astonishes Noddy so much as common sense and plain dealing.
(with apologies to Ralph Waldo Emerson)