That's a good question (you may recognize that as pseudo-expert-ese for
"I don't know"). The thermal efficiency of an internal combustion engine
goes up with temperature, so in that sense hotter is better. But we are
familiar with what happens when we get "too hot", so there is a practical
limit, and it is wise to leave a safety margin as well, for when extreme
conditions are encountered. Fortunately we don't have to worry about the
optimum temperatures for high-tech doodads like oxygen sensors, mass flow
meters, turbocharger bearings, etc. I would say, on the assumption that
your lubricants are up to the task (as any current engine oils should
be), that you would want to run at least 180 degrees under normal
conditions. But frankly, my only evidence for this is the fact that my
temperature gauge reading at dead center is about 185 degrees. That and
the fact that the "normal" MGB thermostat is 180 degrees. Anyway, if this
is true, I don't see any reason to run a cooler thermostat at any season,
even if it did lower the operating temperature (the question would be,
why be less efficient than necessary?). Although running a 190 in winter
just to get a little more "oomph" out of the heater would be fine, since
you aren't in any danger of overheating.
Strictly IMO,
Max
Bruce Burrows had this to say:
>
>--WebTV-Mail-5336-9215
>
>I agree with your analysis (see below) here, Max.
>
>But this is what I do not know:
>
>Setting aside and subordinating all considerations of the need for
>cockpit comfort (either heat or cold), what is the preferred coolant
>operating temperature considering solely what is best for the engine?
>
>For me this would be the controlling factor, wanting as I do to run the
>engine at maximum efficiency and provide best opportunity for extended
>engine life.
>
>Bruce Burrows
>
>'59 MGA basket case
>'60 Daimler SP 250
>'61 Daimler SP 250
>'73 MGB driver
>
>My Dart website (not my cars!):
>
>http://community-2.webtv.net/guardian45/THEDAIMLERSP250DART/
>
>
>--WebTV-Mail-5336-9215
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>Message-Id: <200004212033.NAA25363@harrier.prod.itd.earthlink.net>
>Subject: Re: (Paul) Shroud Question
>Date: Fri, 21 Apr 2000 13:36:48 -0700
>x-sender: mvheim@earthlink.net
>x-mailer: Claris Emailer 2.0v3, January 22, 1998
>From: Max Heim <mvheim@studiolimage.com>
>To: "MG List" <mgs@autox.team.net>
>Mime-Version: 1.0
>Sender: owner-mgs@autox.team.net
>Precedence: bulk
>Reply-To: Max Heim <mvheim@studiolimage.com>
>
>I still don't see how fitting a cooler 'stat makes the engine run any
>cooler, if in warm weather the 'stat is wide open anyway. At this point,
>with the engine fully warmed up and operating at a stable temperature,
>say, 187 degrees, both the 165 and the 180 degree thermostats would be
>wide open, and there would be absolutely no difference between them.
>Meanwhile, a 190 degree thermostat would be cycling open and shut,
>presumably. Now if the ambient temperature were lower, so that the engine
>would reach equilibrium at, oh, 172 degrees, then you would notice an
>effective difference with the "cooler" thermostat. BUT (and this is a big
>"but"), from my experience, at this kind of ambient temperature you are
>more likely to want to run the heater at full efficiency, and are not
>concerned at all with overheating or low oil pressure. In other words,
>it's cold out, and you would prefer the high temperature thermostat at
>this time, anyway. This is why I don't believe in fitting a unreasonably
>low temperature thermostat, like 165 degrees. The engine will never
>stabilize at that low a temperature EXCEPT when it's already cold out
>(and you don't want it to).
>
>Obviously, if you have fitted a larger radiator, larger oil cooler, or
>extra cooling fans, this may not apply to you. But then you have to
>consider whether 165 degrees is the most efficient operating temperature
>for the engine. IMO it is not.
>
>Paul Hunt had this to say:
>
>>The other thing, and the real reason why hotter and cooler thermostats are
>>recommended for extremes of climate (well, extremes when compared to the UK)
>>is that there is always some cooling via the engine surfaces. Small engines
>>in very cold weather may never get up to temperature when cruising, which is
>>why people blank off the radiator in winter. They are not really blanking
>>off the radiator of course because the thermostat is closed anyway, what
>>they are doing is reducing the icy blast through the engine bay and hence
>>the block cooling.
>>
>>When an engine is run in a relatively hot climate there is relatively less
>>block cooling for a given load, so more heat has to travel through the
>>radiator to get cooled, and heat is retained in the engine for longer,
>>raising the internal temperature of the engine above what is ideal. A
>>cooler stat helps to compensate for this reduction in block cooling.
>>Indeed, at one time the cooler stat was fitted as standard in order to
>>increase (or rather restore) oil pressure. This works by reducing the
>>internal temperature of the engine, so running with a cooler stat really
>>does allow the engine to run cooler. Likewise a hotter stat in cooler
>>climes helps to compensate for the *increased* block cooling and resulting
>>lower internal temperatures.
>>
>>PaulH.
>>
>>----- Original Message -----
>>From: Bruce Burrows <bburrows@webtv.net>
>>To: <mgs@autox.team.net>
>>Sent: Wednesday, April 19, 2000 4:39 PM
>>Subject: Re: (Paul) Shroud Question
>>
>>
>>>
>>> --WebTV-Mail-8772-525
>>>
>>> Your reply (which appears below) was a good one, Paul, and much
>>> appreciated. I have to say you forced my mind to work just a bit! Here
>>> is my best take:
>>
>>...
>>
>>
>
>
>--
>
>Max Heim
>'66 MGB GHN3L76149
>If you're near Mountain View, CA,
>it's the red one with the silver bootlid.
>
>
>--WebTV-Mail-5336-9215--
>
--
===============================
Max Heim
mvheim@studiolimage.com
Studio L'Image/San Francisco
415 643 9309 : 415 643 9307 fax
Studio L'Image/New York
212 242 3366 : 212 242 3399 fax
www.studiolimage.com
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