I'm not sure there is anything missing here.
David's measurements were after the oil cooler, 160F to 195F, it would
not be unreasonable to expect a temp before the oil cooler of say 180F
to 225F? I know it depends on the number of rows, the airflow through the
cooler etc, but in the absence of data that is what I'd guess.
So lets say operating temp on average of 200F. Minerals oils start
exhibiting
breakdown at 190F, so that there would be a constant rate of breakdown
of the mineral oils. I'd presume that the rate of breakdown is proportional
(in some non-linear manner) to (T - 190F) up to some point where there is
total and catastrophic breakdown of the oil. This is certainly consistent
with a life between oil changes of say 5000km and the steady blackening
of oil with use. Unfortunately I did not ask what the temp range is for
total
breakdown. I think it is safe to say that it wouldn't happen at anywhere
near "normal operating temperatures".
It would not be surprising to realise that there are conflicting criteria
here,
one for rate of breakdown, one for boiling off volatile compounds and water.
Such is engineering. Personally I don't like the idea of those acidic
compounds eating away the soft metal in the engine (eg bearings), nor
the build-ups of deposits. IMHO, if you use mineral oils, this says you
should
change them regularly and strongly consider an oil cooler.
So you pays your money and makes your choices. It seems to me that
by using synthetic oil, you're stacking the odds in your favour, if not then
an oil cooler does the same for mineral oils.
Mike
-----Original Message-----
From: Ulix Goettsch <ulix@u.washington.edu>
To: Mike Gigante <mikeg@vicnet.net.au>
Cc: spridgets@autox.team.net <spridgets@autox.team.net>
Date: Monday, 15 March 1999 11:39
Subject: Re: Oil and Oil coolers
>Hmmm, this goes against some of the things I have heard in the past.
>Isn't it normal for the oil in an engine to be hotter than the water?
>190F is a normal coolant temp, I would think that the oil is much hotter
>(don't have my oil temp gauge installed yet).
>I was under the impression that the oil had to get this hot for water and
>other things to evaporate out of the oil. I seem to recall a oil temp
>target of 210 to 220 degrees, but I can't remember the exact number.
>
>If this is true, your point 1) would not be a good idea (keeping oil temp
>under 190F). But would anyone really use mineral oil if it was
>experiencing constant and significant breakdown with serious consequences
>at normal operating temperatures?
>
>I am not arguing very scientifically here, but something doesn't seem to
>add up, maybe a piece of information is missing.
>Ulix
>
>
>
>On Mon, 15 Mar 1999, Mike Gigante wrote:
>
>> Over on the MGs list, there has been a discussion of the usefulness
>> or otherwise of oil coolers on the street.
>>
>> One lister, David Darby, reported that
>>
>> "During summer operation ambient temps can reach 100 F or more. August is
>> our
>> warmest month with daily high temps averaging about 95 F. The highest
I've
>> seen the (Stewart-Warner) oil temperature gauge go is about 195F. It
>> normally runs 160F to 180F. I am measuring the oil temperature at the
union
>> between the return oil line and the engine block.
>>
>> Those are my half-baked observations on oil temp in my own MGB. YMMV."
>>
>> Note that David is running an oil cooler and that the oil temp gauge is
>> sampling temperature immediately after it has been through the oil
cooler.
>>
>> Over the weekend I spoke to a scientist at a major oil company and this
>> is what she had to say:
>>
>> "Mineral oils start to break down at 88C (190F) whereas synthetic oils
>> begin to breakdown at 200C (392F).
>>
>> Byproducts of mineral oil breakdown include acids and carbon soot.
>> The carbon soot tends to fall out of suspension causing deposits
>> throughout the engine.
>>
>> Byproducts of breakdown in synthetics remain in solution (hence no
>> deposits)."
>>
>> So, I think this clearly sends two messages
>>
>> a) if you use mineral oils, an oil cooler is a pretty damn good idea
>> if your oil temps are likely to approach 88C. From David's data, it seems
>> very likely that a significant portion of listers will see this on a
regular
>> basis.
>>
>> b) you should seriously think about using synthetics! I have been doing
>> so for the past 5 years or so and I have no complaints!
>>
>> Mike
>>
>>
>>
>>
>
> Ulix __/__,__ ___/__|\__
>..............................................(_o____o_)....<_O_____O_/...
> '67 Sprite '74 X1/9
>
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